GARY PADGETT'S MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY AUGUST, 2001 (For general comments about the nature of these summaries, as well as information on how to download the tabular cyclone track files, see the Author's Note at the end of this summary.) SPECIAL NOTE: Tony Cristaldi of the NWS office in Melbourne, Florida, rather inadvertently "discovered" a hitherto unreported tropical (or possibly subtropical) cyclone which occurred in the Southwest Indian Ocean in April. According to Philippe Caroff of the La Reunion TCWC, this system formed to the south of Reunion's AOR; therefore, no warnings were issued on the cyclone. This system is being researched and hopefully more information and a track will be forthcoming in a couple of months. *********************************************************************** AUGUST HIGHLIGHTS --> Western North Pacific very active, but no typhoon landfalls --> Three tropical storms in the Atlantic fall just short of reaching hurricane intensity *********************************************************************** ***** Feature of the Month for August ***** RESULTS OF TROPICAL CYCLONE SURVEY - PART 4 MONSOON DEPRESSIONS As promised I am trying to wrap up reporting on the responses to my tropical cyclone survey that I sent out last March. I have covered the topics of cyclone size as a possible classification criteria (May Feature), classification of subtropical/hybrid cyclones (June Feature), and warning strategies for subtropical/hybrid cyclones (July Feature). This month I will summarize the few opinions I received on the subject of monsoon depressions. Exactly what is a monsoon depression? The definition of a monsoon depression which used to be given in the Annual Tropical Cyclone Report published by JTWC reads as follows: "A monsoon depression is a tropical cyclonic vortex characterized by (1) its large size, the outer-most closed isobar may have a diameter on the order of 600 nm; (2) a loosely-organized cluster of deep convective elements; (3) a low-level wind distribution which features a 100 nm diameter light-wind core which may be partially surrounded by a band of gales; and (4) a lack of a distinct cloud system center." Monsoon depressions do not occur in all tropical cyclone basins. They are extremely rare in the Atlantic basin: one occurred in the western Caribbean in May, 1986, and Tropical Storm Frances of 1998 in its earlier stages had the appearance of a monsoon depression. The main regions where they seem to develop most frequently are the North Indian Ocean, the tropical Northwest Pacific basin, the vicinity of northern Australia and occasionally the South Pacific. Philippe Caroff of the La Reunion TCWC indicates that they are very rare in the Southwest Indian Ocean. Jack Beven years ago related to me that an occasional Eastern Pacific tropical cyclone seemed to have monsoon depression characteristics. Mark Lander has told me that on infrequent occasions monsoon depressions will form in the austral autumn over Africa south of the equator and sometimes move westward over the South Atlantic. Such a system may have been responsible for the development of the only known South Atlantic tropical cyclone to date--a strong tropical depression or perhaps minimal tropical storm in April, 1991. Some of the stronger African waves which move out into the Cape Verde region also occasionally display some monsoon depression features. Since classic monsoon depressions are an extremely rare feature in the Atlantic basin, the NHC forecasters who responded to my survey didn't have all that much to say. James Franklin indicated that he would probably treat a monsoon depression (with gales) as a non- tropical gale center. Jack Beven posed the question "how small does the core of a cyclone have to become for the system to be considered tropical? From a theoretical standpoint the threshold would be when the tropical cyclone energetics become predominant. From a practical standpoint, I don't know the right criteria or data to make such a determination objectively." Philippe Caroff, in response to the question about spatial distribution of gales within a circulation, indicated that for a system in which gales are well-removed from the center (such as in a monsoon depression), he felt that such gales should fairly well encompass the center before the system was named as a tropical storm. Matthew Saxby of Australia is in favor of naming monsoon depressions with gale-force winds as tropical cyclones because their greater size would likely make them more damaging. David Roth of HPC writes, "I know monsoon depressions can mock subtropical cyclones when it comes to maximum winds being well-removed from the center. Any radius should work, as long as the winds are caused by some direct effect of the existence of the LOW, like increased pressure gradient, and the system is deeply warm-core (to at least 500 mb)." In his reply to the question about spatial distribution of gale-force winds as a criteria for classification as a tropical cyclone, Rich Henning wrote, "I personally don't think there should be a minimum for all the quadrants. If there are 50-kt winds in the northeast quadrant of a monsoon-type cyclone, and only 15 kts in the southwest quadrant...it is still a tropical cyclone." Although Mark Lander did not respond to my survey, I know from past correspondence and postings from Mark that he does consider monsoon depressions which have developed bands of gales within the circulation to be bonafide tropical cyclones worthy of having warnings issued. In a letter posted to some discussion lists in September, 1998, after the development of Tropical Storm Frances in the Gulf of Mexico, Mark pointed out that in the Northwest Pacific basin, monsoon depressions are the systems which are the precursors of most of the typhoons, especially those originating in the deep tropics. Most monsoon systems which achieve winds of 30 kts go on to become "conventional tropical cyclones" (i.e., with organized central convection and tighter gradients). Winds can increase in these systems to 50 kts in some portions before persistent central convection is established. To quote Dr. Lander, "Attempts to say that this is due to the gradient between the LOW and some high pressure area, or any other line of reasoning to avoid calling it a tropical storm, are misleading, and a danger lurks. As soon as persistent central convection develops, one has instantly a large, full-fledged 'conventional' tropical storm (or even near hurricane or typhoon), and has to suddenly go to a tropical cyclone warning with an embarrassingly high initial intensity." Mark also wrote that "the JTWC has for years had trouble with these systems. People say they are not tropical cyclones; that they are hybrid systems of some sort; that they are not warm core--the explanations are legion. Most of the time the effort goes into explaning why a tropical cyclone warning should not be issued on such systems. Part of the problem is the Dvorak tropical cyclone classification system. Largely developed from Atlantic tropical cyclones, Dvorak defines four basic patterns of (for lack of a better word) 'conventional tropical cyclones': (1) shear pattern, (2) curved- band pattern, (3) CDO pattern, and (4) eye pattern. Monsoon depressions do not fit neatly into this scheme and are not common in the Atlantic. Thus, Dvorak's techniques do not address them." In closing I'll include the reply I received from Julian Heming of the UK Meteorological Office. Julian's reply didn't address the specific questions I'd raised, but rather shed light on the impact of the issuance or non-issuance of warnings on the performance of numerical models. Julian wrote: "I've seen various views aired on this subject in the past and I probably haven't got too much to add to those who are more at the 'cutting edge' of tropical cyclone warning strategies. However, from the (UK) Met. Office's point of view, the most important thing is to have good information to use in initialising cyclones (be they tropical, subtropical, midgets, etc) in our model. For us that means receipt of a warning or advisory from the relevant tropical cyclone warning centre. If a warning centre decides not to name a cyclone and does not issue a warning because it is not a 'classical tropical cyclone', then our model (and I presume other models which use advisories in their initialisation procedures) will not have the benefit of information produced by tropical analysts. This could possibly result in an inferior model forecast. Of course, if a cyclone is too far removed from being a true tropical cyclone, then it may not be appropriate to use some initialisation techniques, but I think on most occasions having some information to feed the model is better than none at all. I'm sure there will be arguments made for not issuing warnings until a cyclone is truly tropical, but I thought I'd present the viewpoint from one involved in model initialisation of tropical cyclones." I'd like to thank everyone who took the time to respond to my survey, and I hope that these ideas and opinions I've presented will, in a small way, lead to further discussions among tropical cyclone forecasters and researchers with the goal in mind of trying to forge a more globally consistent set of classification criteria and warning strategies for these various types of marginal tropical cyclones. *********************************************************************** ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for August: 3 tropical storms NOTE: Much of the information presented below was obtained from the TPC/NHC discussion bulletins issued with every regular advisory. All references to sustained winds imply a 1-min averaging period unless otherwise noted. Some information was also obtained from the monthly summary for August prepared by the Hurricane Specialists and available on TPC/NHC's website. Atlantic Tropical Activity for August ------------------------------------- Following Tropical Storm Allison in early June, the Atlantic basin remained quiet save for one short-lived minor tropical depression in July. The tropical cyclone season, however, began to get underway in earnest early in August with the development of Tropical Storm Barry in the eastern Gulf of Mexico. Barry made landfall in the Panhandle of Northwestern Florida during the night of 5-6 August just shy of hurricane intensity. Tropical Storm Chantal developed on 16 August east of the Windward Islands. The storm was moving so rapidly it lost its circulation and was downgraded to a tropical wave later that day. The next day it regained its circulation and was re-upgraded to a tropical storm in the central Caribbean. Chantal moved westward and eventually made landfall near Chetumal, Mexico, around 0000 UTC on 21 August as a strong tropical storm. Tropical Storm Dean developed rather suddenly just north of the Virgin Islands on 22 August. However, the storm encountered a hostile shearing environment and weakened to a tropical wave the next day. Some of the convection associated with Dean moved northward, interacted with a non-tropical LOW, and eventually redeveloped into a tropical cyclone south of the Canadian Maritimes. During its second incarnation Dean almost became a hurricane before encountering cooler waters and increased shear in the North Atlantic. Three named storms is about normal for August, but the lack of a hurricane is somewhat unusual--the average (1950-2000) is 1.55. The last August which didn't produce a hurricane was in 1997--there were no tropical storms or depressions either. The disintegration of two named storms back to tropical waves followed by their subsequent redevelopment to tropical storm intensity was also unusual. This trend, strangely, continued into September as both Tropical Storm Erin and Tropical Depression 07 (pre-Felix) were downgraded to tropical waves but subsequently regained their circulations and went on to become major hurricanes. Tropical Storm Barry (TC-03) 2 - 7 August ----------------------------- A. Origins ---------- Barry was the first tropical storm of the 2001 season to form from an African tropical wave, but that development didn't occur until the system had reached the southeastern Gulf of Mexico. The parent wave was located in the eastern Atlantic south of the Cape Verdes on 25 July and was moving rapidly westward. By the 26th the disturbance was located around 1400 nm east of the Windward Islands. Atmospheric conditions were not favorable for intensification and there was little associated convection. The wave entered the eastern Caribbean area on 29 July. The convection was not well-organized but pressures had fallen a bit and the system was producing showers, thunderstorms, and gusty winds over portions of the Lesser Antilles. The tropical wave continued westward across the Caribbean--on the 31st it was generating showers and thunderstorms from the central Caribbean northward across Hispaniola into the southeastern Bahamas; however, there were still no signs of increasing organization. Early on 1 August scattered showers and a few thunderstorms extended from the northwestern Caribbean northeastward across Jamaica, eastern Cuba, and into the Bahamas and were forecast to spread across western Cuba and southern Florida later in the day. The TWO noted that some slow development was possible over the next day or two. During the afternoon satellite imagery and surface observations indicated that the convection was becoming better organized near Dry Tortugas Island in the southeastern Gulf of Mexico. The weak surface LOW changed little in organization during the night; it was interacting with a small upper-level LOW and upper-level winds were not favorable for rapid intensification. Most models, however, suggested that tropical cyclogenesis would occur, and during the morning of the 2nd the LOW began to show signs of intensification. TPC/NHC issued a Special Tropical Disturbance Statement at 1330 UTC which stated that surface observations and visible satellite imagery were indicating that a tropical depression might be forming. An Air Force reconnaissance place reached the area around midday and found 48-53 kt winds at 300 m, so the LOW was upgraded directly to Tropical Storm Barry in a special advisory at 1900 UTC. Barry, which was then located about 270 nm south-southeast of Fort Walton Beach, Florida, was more of a hybrid storm at that point than a purely tropical system as it was still sort of tangled up with the upper-level LOW. B. Track and Intensity History ------------------------------ After being upgraded to a tropical storm, Barry strengthened to 40 kts as it moved slowly west-northwestward. Late on the 3rd the storm slowed to an erratic drift a couple hundred miles south of the western Florida Panhandle, remaining in this general area until early on the 5th, when it began a steady northward march toward the coast. Barry had weakened to a minimal tropical storm by 0600 UTC on 3 August, and operationally remained at that intensity for 48 hours. However, reconnaissance flights during the night of 3-4 August and on the 4th could find no tropical storm-force winds. The Monthly Summary for August prepared by the staff of NHC indicates that Barry weakened to a depression on 3 August, and it seems likely that will be reflected in the final storm report and Best Track. Since the pressure remained steady during this period and the circulation of Barry was large and well-defined, it was maintained as a minimal tropical storm in real time, although a couple of NHC discussions indicated that Barry very possibly was only a tropical depression. Barry began to show signs of re-intensification during the evening of the 4th as very deep convection with cold cloud tops reaching -81 C at times blossomed near the LLCC. A reconnaissance flight around 1200 UTC on 6 August found that the pressure had fallen 14 mb in six hours to 990 mb. A special advisory was issued at 1300 UTC to post hurricane warnings from Pascagoula, Mississippi, eastward to the Ochlockonee River in northwest Florida. Tropical storm warnings were already in place for portions of the coast, and these were extended eastward to the mouth of the Suwanee River. Tropical Storm Barry reached its peak intensity of 60 kts around this time, but the intensification trend leveled off and the storm remained at just under hurricane intensity until landfall early on the 6th. Barry's center made landfall around the middle of the night of 5-6 August about 30 km east of Fort Walton Beach between the Walton County communities of Miramar Beach and Grayton Beach. The weakening cyclone continued inland across the Panhandle, moving just east of Crestview, and northward into southern Alabama, passing over or very near the author's home near Andalusia. Barry turned to a northwestward track as it marched inland and had weakened to a tropical depression over southwestern Alabama by 1500 UTC on the 6th. The remnant LOW speeded up somewhat for a time after landfall and had reached the Alabama-Mississippi border near Aliceville, Alabama, by 2100 UTC. HPC had assumed responsibility for issuing storm summaries after Barry was dropped by NHC, and the fourth and final HPC summary, issued at 1500 UTC on 7 August, indicated that the weak remnants of Barry were located near Memphis, Tennessee. They were last seen over south- eastern Missouri on the 8th. C. Meteorological Aspects ------------------------- Barry was upgraded to a tropical storm at 1900 UTC on 2 August. By 2100 UTC convection had wrapped more than halfway around the LLCC and outflow was good in the eastern semicircle. A reconnaissance plane found 54-kt winds at 300 m and a pressure of 1008 mb. Some south- westerly vertical shearing was hampering Barry at this time. The NHC discussion issued at 03/0300 UTC, written by Jack Beven, provides a good example of some of the difficulties encountered in following tropical cyclones even with multiple observational platforms available. Reconnaissance fixes indicated that the center was moving west or west- northwest at about 10 kts. However, satellite fixes, including some good visible pictures, suggested the center was moving north or even east of north. Furthermore, data from Buoy 42003 supported the aircraft fixes while the Tampa WSR-88D radar supported the satellite positions! The best conclusion seems to be that the center was tilted due to the southwesterly shear and that satellite and radar were tracking the upper-level center. Early on the 3rd, strong upper-level westerlies became established over Barry and the LLCC became detached from the limited convection. Later during the morning some convective organization was regained, and a reconnaissance flight found 35-40 kt winds and a pressure of 1007 mb. The westerly shear continued to decrease during the afternoon and Barry's appearance continued to improve. However, no sooner had Barry begun to recover from the westerly shear when it was hit by strong northeasterly flow associated with a cyclonic shear axis which had moved over the storm. Barry likely weakened to a tropical depression during the night of 3-4 August--a couple of reconnaissance flights could find no winds of tropical storm intensity. However, the pressure had dropped to 1005 mb and satellite intensity estimates from TAFB and AFWA were 35 kts, so the cyclone was maintained as a minimal tropical storm. A flight during the morning of the 4th reported a pressure of 1006 mb and winds to 39 kts south of the center. During the evening of 4 August another reconnaissance mission found flight-level winds of 44 kts and a minimum pressure of 1003 mb. The storm was slowly improving in organization, and during the early morning hours of the 5th, Barry developed some very deep convection with cold cloud tops to -81 C at times near the LLCC. The center was not embedded in the deepest convection but rather was on the north- western edge due to some west-northwesterly shear which had developed ahead of a shortwave trough that was digging down over Arkansas and Louisiana. The MSW was increased to 40 kts at 0900 UTC based on TAFB and SAB estimates of T3.0. A reconnaissance flight around 1200 UTC found that the pressure had fallen 14 mb to 990 mb in a six-hour period. Winds were upped to 50 kts and the hurricane warnings were ordered for portions of the Gulf Coast. This rapid intensification, however, did not continue throughout the day. The structure of Barry had been changing with the development of outer banding features in the eastern semicircle which seems to have isolated the inner core and slowed the intensification process. Also, the westerly shear over the storm had likely brought some drier air into the inner core. Barry did not weaken, however, as a dropsonde released at 1900 UTC reported surface winds of 61 kts. During the night of 5-6 August, WSR-88D radar observations showed transient eyewall formations, but the inner core never became better defined with the eyewall remaining open over the southern semicircle. A reconnaissance flight at 06/0451 UTC found a 700-mb flight-level wind of 71 kts southeast of the center and an extrapolated minimum pressure of 990 mb. The last dropsonde into the storm, at 0335 UTC, with the center still about 17 nm offshore, had reported a SLP of 993 mb. After Barry's center had made landfall and crossed over Choctawhatchee Bay, it passed near Eglin AFB range station C-52 (30.6N, 86.3W) where the altimeter reached a minimum of 994.2 mb at 0547 UTC with southeasterly winds of 25 kts, gusting to 37 kts. The strongest gust was 52 kts from the northeast at 0516 UTC. The peak gust reported at the Eglin Main weather station (around 15 km to the west-southwest) was 270/55 kts at 0627 UTC; the sustained wind at the time was 33 kts. Destin, Florida, reported a gust of 37 kts around midnight when Barry's center was about 17 nm east-southeast of that location and the northern eyewall had already moved onshore. Cape San Blas, well to the east, reported a peak gust of 36 kts. Tyndall AFB near Panama City recorded 186 mm of rainfall in the 24 hours ending at 06/1200 UTC with another 8 mm falling during the next six hours. Eglin AFB had recorded 94 mm by 1400 UTC on the 6th. The first storm summary issued by HPC included some 5-day rainfall totals for Barry ending at 06/1200 UTC. Many locations in the southern portion of the state experienced heavy rainfall associated with the tropical wave which spawned Barry and during the storm's early formative stages. Tynfall AFB's 5-day total was 220 mm followed by 204 mm at the West Palm Beach International Airport. Fort Lauderdale recorded 202 mm during the 5-day period. Quite a few locations over the state had totals between 150 and 175 mm. Tallahassee recorded 156 mm for a 5-day total ending at 1800 UTC--for the 12-hour period 06/1200 UTC through 07/0000 UTC that site picked up 109 mm. During the 30 hours ending at 1800 UTC on 6 August, Apalachicola measured 156 mm. The highest 3-day storm total, ending at 07/1200 UTC, was 226 mm at Tallahassee. Rainfall amounts tapered off considerably as Barry weakened and moved across Alabama. Maxwell AFB near Montgomery recorded a 24-hour total of 70 mm, ending at 07/1200 UTC, while the Shelby County Airport picked up 59 mm for the same period. Some storm totals in Alabama for the 72-hour period ending at 07/1200 UTC include 103 mm at Troy, 89 mm at Ozark, and 82 mm at Maxwell AFB. Valdosta, Georgia, well-removed from Barry's track, recorded 61 mm for the same period while Tupelo, Mississippi, measured 27 mm for a 3-day total. D. Damage and Casualties ------------------------ Winds and rain associated with Tropical Storm Barry caused minor damage in the Florida Panhandle amounting to about $30 million. No deaths were attributed to the storm. Tropical Storm Chantal (TC-04) 15 - 22 August ------------------------------- A. Origins ---------- Tropical Storm Chantal was one of the oddest and most troublesome Atlantic tropical cyclones in recent years. It was the first of four consecutive "interrupted" cyclones--systems whose centers dissipated only to regenerate later. Chantal was also one of the most rapid movers on record for the deep tropics, racing across the tropical Atlantic and central Caribbean at speeds of up to 25 kts at times. This rapid motion resulted in Chantal's having a great difficulty main- taining a well-defined closed circulation even after it regenerated in the southeastern Caribbean. It's not far from the truth to say that Chantal was almost an open wave with winds to near hurricane force--something which "just isn't supposed to happen". Like Barry before it, Chantal did slow down and become better organized and was near hurricane intensity when it made landfall near Chetumal, Mexico. A tropical wave left the west coast of Africa around 12 August, producing a large area of showers and thunderstorms but not very well organized. By the next day there had been a slight increase in convective organization and a TWO indicated that the system had some potential for slow development over the next couple of days. Early on the 14th the wave was even better organized, and was accompanied by a broad area of low pressure but still lacked persistent central convection. By 1500 UTC on 15 August the wave had acquired enough organized convection that it was upgraded to Tropical Depression 04, located about 900 nm east of Barbados. The center was poorly-defined and appeared to be located east of the main convection, but since low shear and warm waters were ahead of the depression, intensification was forecast. A strong mid-level ridge to the north was steering TD-04 westward at 20 kts or more. By the early morning of 16 August, TAFB was estimating 35 kts (the other agencies were lower), and the depression appeared to be very near tropical storm strength. The NHC specialist on duty opted to wait until visible satellite pictures were available before upgrading in order to get a better handle on the center location. The depression was moving westward at about 24 kts at the time. An intermediate advisory was issued at 1200 UTC, upgrading the system to Tropical Storm Chantal, located about 325 nm east of Barbados. B. Track and Intensity History ------------------------------ The cloud pattern of Chantal had improved since the previous day with banding features and excellent outflow due to an upper-level anti- cyclone located over the tropical cyclone. However, there was a very big surprise when the first Hurricane Hunters' reconnaissance mission reached Chantal during the early afternoon. The crew was not able to locate any closed circulation at the surface. Chantal exhibited the cloud pattern of a fairly well-defined tropical cyclone, but the rapid translational speed had led to the storm's being unable to maintain its surface circulation--if it had ever existed at all. The NHC Monthly Summary suggests that possibly Chantal was not a bonafide tropical storm on 16 August. It will be interesting to see how this phase of Chantal's life is handled when the final storm report becomes available later. A special advisory was issued at 07/0000 UTC downgrading Chantal to a tropical wave about 100 nm west of Barbados. Even as a tropical wave, the system produced winds to tropical storm force on Martinique as it passed through the Windward Island chain. By the morning of the 17th convection had greatly increased and the system exhibited a very impressive cloud pattern. After looking very hard, a reconnaissance plane found a small 1010-mb center about 330 nm south-southeast of San Juan, Puerto Rico, so advisories were commenced once more on Chantal at 1500 UTC. The depression was still moving rapidly westward at 23 kts; nonetheless, another flight during the afternoon found a well-defined center with a pressure of 1006 mb and winds strong enough to justify upgrading the system back to tropical storm status, so Chantal became a tropical storm once more at 2100 UTC with 35-kt winds, located about 250 nm south of San Juan. Based on reconnaissance reports during the night, by the morning of 18 August Chantal's MSW had been increased to 50 kts, but the 1500 UTC advisory noted that satellite imagery revealed an exposed LLCC moving rapidly to the west-northwest, leaving the mid-level circulation and most of the convection behind. Reconnaissance planes, however, had found winds exceeding hurricane force at flight level (450 m), so in spite of the very disorganized appearance, Chantal continued to maintain rather strong winds and even intensified some. By 1200 UTC on 19 August, the storm had reached an initial peak intensity of 60 kts at a point about 215 nm southwest of Kingston, Jamaica, even though all the strong winds were in the northeastern quadrant. To the south of the broad and ill-defined center only light and variable winds were found. (More on this particular reconnaissance flight below.) Chantal's forward motion slowed some on the 19th and 20th, but the benefits of the slower translational speed were offset by some shear from an upper-level trough over the western Caribbean. The storm struggled to survive as a tropical cyclone, but the intense convection helped to maintain fairly strong winds and the MSW was never lowered below 55 kts during this period. As Chantal approached the Yucatan Peninsula on 20 August, the shear began to relax and the storm responded by developing a better-defined center and intensifying right up to the moment of landfall. The MSW was estimated at 60 kts once again as the center made landfall near Chetumal, Mexico. The 21/1500 UTC discussion noted that even though the center of Chantal had been over land for around 12 hours, the satellite signature was the best that it had been during the storm's history. Chantal was originally forecast to move west-northwestward across the Yucatan Peninsula and emerge into the Bay of Campeche with a chance of re-intensifying. However, by 2100 UTC on the 21st convection had decreased significantly and most of what was left was over the Caribbean well removed from the center. Chantal was downgraded to a 30-kt depression; the system, however, was still showing anticyclonic outflow. By 22/0300 UTC convection had continued to diminish and the mid-level center had sheared off to the northeast. Even though a reconnaissance flight found 25-35 kt winds at flight level over the Bay of Campeche to the north, the low-level center turned to the south- west and began to dissipate over southeastern Mexico. The final advisory on Tropical Depression Chantal, at 22/1200 UTC, placed the dissipating center near Villahermosa, Mexico. C. Meteorological Aspects ------------------------- Reconnaissance flights into Chantal on 18 and 19 August reported some unusual happenings. A flight during the evening of the 17th reported 58-kt winds at 450 m north of the center with a central pressure of 1004 mb. Convection was more concentrated but the crew reported that the circulation at flight level was not well-defined. A reconnaissance mission around 18/0600 UTC reported winds to 73 kts at 450 m, but this was adjudged to likely be due to mesoscale convective effects. During the morning of the 18th satellite imagery revealed an exposed LLCC moving rapidly west-northwestward away from the mid-level circulation and convection; nonetheless, a reconnaissance plane fixed another weak center to the south with flight-level winds of 67 kts. Chantal had become disorganized with an elongated center. During the afternoon it became apparent that unexpected shear from an upper-level trough over the western Caribbean was the culprit that was disrupting Chantal's cloud pattern, which consisted of a very tight center of low clouds to the west of a strongly-curved band of deep convection. Reconnaissance data during the afternoon showed a pressure of 1003 mb and 50-60 kt winds in the band of convection. The most unusual reconnaissance missions occurred early on the morning of 19 August. The flight around 0600 UTC reported 62-kt winds at 450 m in the southeast quadrant with the pressure down to 997 mb-- a drop of 6 mb since the previous mission. Satellite intensity estimates were running around 45-55 kts, but the center was fixed on the western edge of the deep convection, whereas the reconnaissance crew placed the center farther back into the deep convection. Thus, it appeared that Chantal's forward motion had slowed dramatically and that the storm was forming an eye and possibly embarking on a spell of rapid intensification. The 1200 UTC reconnaissance was most extraordinary. Rich Henning was present on that flight and has personally related to me some of the surprises they found. They flew into Chantal expecting to find a hurricane but barely found a closed circulation. Because of some deep convection with very intense lightning and likely strong updrafts and downdrafts, the aircraft entered the storm at a higher altitude (around 1500 m) than the earlier flights. The plane approached the center from the northeast and 82-kt winds were observed in that quadrant. However, no eye was found, and they eventually broke out of the convection into a large, broad area of light and variable winds well southwest of the main area of deep convection. The lowest pressure found was 1004 mb. Rich stated that it was with great difficulty that they found enough of a circulation to justify a vortex fix. Only very light and variable winds could be found to the south of the broad center. Two subsequent flights through the northeast quadrant found peak winds of 72 kts and 62 kts, respectively. What seems to have happened was that during the night Chantal had made an attempt at forming a tight vortex, but that it failed to develop further and the storm was weakening by the time the 1200 UTC mission reached the area. Chantal remained in a disorganized state until the morning of the 20th when it began to show somewhat better organization. A flight into the storm around 0000 UTC found the storm still poorly-organized with the LLCC about 100 nm to the west of the nearest deep convection. The reconnaissance crew reported flight-level winds of 69 kts, but the dropsonde released at that point measured surface winds of only 38 kts. Chantal was not effectively transporting momentum to the surface. Reconnaissance fixes were consistently to the south of the low-level cloud swirl, which implied that the surface wind center lay to the south of the low-level vorticity center. The next reconnaissance mission into the storm at 0532 UTC found a better-defined circulation, and satellite imagery indicated that a large thunderstorm cluster had developed over or near the LLCC. The peak flight-level winds found were 61 kts at 850 mb at 0552 UTC. By afternoon Chantal's appearance was still better--satellite imagery portrayed a comma-shaped cloud pattern with the center near the edge of the dense overcast, the southern portion of the circulation had become distinct, the strongest winds in the northeast quadrant were nearer the center, and water vapor loops suggested that the shear was decreasing. Reports from USAF reconnaissance flights and a NOAA P-3 research mission revealed that Chantal continued to strengthen right up to the time of landfall near Chetumal. A dropsonde in deep convection north- east of the center at 20/2144 UTC measured 58-kt winds at the surface and the peak flight-level wind was 71 kts--these values corresponding to a surface MSW of 60 kts. Right at landfall there was a burst of deep convection very close to the center. The NHC advisory at 0900 UTC stated that surface observations from Chetumal and Belize, along with radar reports, indicated that Chantal had either stalled or had developed a new center farther south and east of the previous advisory position. Radar data at 0800 UTC indicated that an eyewall was trying to close off between San Pedro and Corozal. As noted earlier, Chantal's satellite signature continued to improve for a while after the center had moved inland. D. Damage and Casualties ------------------------ No fatalities were associated with Chantal while it was a tropical cyclone, although two deaths were reported in Trinidad due to lightning associated with the passage of the tropical wave through the Lesser Antilles. Damage in Belize was estimated at $10-15 million, and there were no reports of significant damage in Mexico. Tropical Storm Dean (TC-05) 22 - 29 August ---------------------------- A. Origins ---------- Unlike its two predecessors, Dean's formation doesn't seem to be directly related to a wave of African origin. Based upon information taken from TPC's Tropical Weather Discussions, the progenitor of Dean seems to be a disturbance initially located on the ITCZ that detached itself and headed west-northwestward. The disturbance was first mentioned at 1800 UTC on 18 August when located near 13.0N, 35.0W, with an associated 1015-mb LOW. By the early morning of the 19th the wave was located about 1400 nm east of the Windward Islands. It was not too well-organized but was showing signs of increased convective organization. On the 20th the disturbance had moved to a position about 650 nm east of the Windwards and shower activity was still limited. Convection increased on the 21st when the wave was located about 450 nm east of the Lesser Antilles. A TWO noted that upper-level winds were not favorable for rapid development but some slow organization was possible. A reconnaissance flight by the Hurricane Hunters during the afternoon of 21 August was unable to locate a closed LLCC. The wave was moving rather rapidly west-northwestward at 20 kts; it was well-organized but upper-level winds were inhibiting development. On the morning of the 22nd the wave appeared much better organized based on surface, radar and satellite observations. The system was moving west-northwestward at 18-22 kts through the northern Lesser Antilles and upper-level winds were becoming a little more favorable for strengthening. The next reconnaissance mission into the disturbance on the after- noon of 22 August found a surprise--a small 1010-mb center located north of the Virgin Islands with 65-kt winds at 300 m over the north- east quadrant. Therefore, advisories were initiated immediately on Tropical Storm Dean with 50-kt winds. Dean's center was located at the time about 115 nm east-southeast of San Juan and moving west- northwestward at 22 kts. The center was exposed on the western edge of the deep convection, and the NHC discussion noted that some of the observed strong winds were likely due to the rapid translational speed. On the last pass of the reconnaissance plane through the storm, a 1009-mb center was fixed and maximum flight-level winds were 63 kts. The center was exposed at the northern end of a convective band trailing southward across the Virgin Islands. B. Track and Intensity History ------------------------------ Exactly what factors led to the sudden intensification of the tropical wave into a fairly strong tropical storm aren't clear, but the intensification trend certainly did not continue. The 23/0300 UTC advisory noted that a recent QuikScat pass had showed an open wave, leading to the possibility that Dean no longer possessed a closed circulation. The small storm had moved into a region of fairly strong vertical shear and found it to be more than it could withstand. Nighttime infrared imagery suggested the possibility of multiple circulation centers, and a reconnaissance flight during the morning of the 23rd was unable to locate a closed surface circulation. The plane found a minimum pressure of 1013-1014 mb with maximum flight-level winds of 42 kts east of the remnant low-cloud swirl. So a final advisory on Dean was issued at 1500 UTC placing the dissipating center about 325 nm northwest of San Juan. The remains of former Tropical Storm Dean moved northward ahead of a slow-moving frontal boundary lurking off the U.S. East Coast. By the morning of the 24th satellite images indicated that Dean's remnants had become better organized with a possible broad surface circulation forming about 350 nm west-southwest of Bermuda. A reconnaissance mission into the disturbance during the afternoon found a broad 1011-mb LOW with a weak wind field about 300 nm west- southwest of Bermuda, moving north-northeastward at around 13-18 kts. The weak LOW interacted with a non-tropical trough to its west, and by 1200 UTC on the 25th the two systems had merged to form a hybrid depression roughly 150 nm northwest of Bermuda. During the 26th ships began to report gale-force winds and convection slowly increased around the center. Early on 27 August a ship with call sign WGMJ reported southerly winds of 55 kts with a SLP of 1004 mb near the center of the cloud mass. Since the system had intensified and taken on a more tropical appearance once more, advisories were re-initiated on Tropical Storm Dean at 27/0900 UTC. The storm was centered at 0600 UTC about 425 nm south-southeast of Halifax, Nova Scotia, and was moving northeastward at 16 kts. The cyclone subsequently attempted to form a banding eye, and the MSW was increased to 60 kts at 1800 UTC when Dean was centered about 475 nm southwest of Cape Race, Newfoundland. Convection began to decrease early on the 28th with the center defined by a swirl of low- to mid-level clouds east of the primary convection. At 0500 UTC a Canadian buoy (44141) reported a pressure of 1004.3 mb and 5.5 m seas 55 nm southeast of the center. As Dean began to move over colder SSTs of 22 C or less, cool and dry air began to work into the system, the pressure fields began to broaden, and the storm began to rapidly weaken and lose tropical characteristics. The final NHC advisory was issued at 1500 UTC on the 28th and placed Dean about 200 nm south of Cape Race. The storm was fast becoming extratropical as it accelerated to the east- northeast. David Roth considers the system to have re-assumed a sort of hybrid/subtropical appearance for a day or so as there was limited convection southwest and north of the center. Transition to an extratropical cyclone was complete by 30/0000 UTC as all convection had disappeared and the system had become linked to a baroclinic band as seen in satellite imagery. The final position in David's track places the extratropical gale over 500 nm east-northeast of Cape Race. C. Meteorological Aspects ------------------------- Since Dean had such a short life as a tropical cyclone, including both phases, all the information received by the author from surface observations and reconnaissance missions has been incorporated into the above paragraphs detailing the storm's track and history. D. Damage and Casualties ------------------------ Winds to tropical storm force were reported in the U. S. Virgin Islands, and there was some damage due to flooding in Puerto Rico. Total damage is estimated at about $2 million. No deaths were attributed to Tropical Storm Dean. *********************************************************************** NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for August: 1 tropical depression 1 hurricane NOTE: Much of the information presented below was obtained from the TPC/NHC discussion bulletins issued with every regular advisory (CPHC for locations west of 140W.) All references to sustained winds imply a 1-min averaging period unless otherwise noted. A special thanks to John Wallace of San Antonio, Texas, for writing the summary on Hurricane Flossie. Northeast Pacific Tropical Activity for August ---------------------------------------------- The month of August on the average sees about four named storms develop in the Northeast Pacific basin. Two of these will reach hurricane intensity with one becoming a major hurricane (Category 3+ on the Saffir/Simpson scale). August, 2001, was definitely a quieter than normal month in this basin. Only one tropical storm developed, Flossie, although it did become a Category 2 hurricane. In addition to Hurricane Flossie, one short-lived tropical depression was tracked in the Eastern Pacific during August. This depression can be traced back to a tropical wave which left the west African coast around 7 August. The wave made its way westward across the Atlantic and Caribbean Sea, reaching the Eastern Pacific by the 17th. Once in the Pacific the disturbance continued moving rather rapidly westward, and by 21 August had reached the vicinity of 132W, or about 1300 nm east-southeast of the Hawaiian Islands, and was showing some signs of increased organization. The next day a good low-level circulation was evident in the low clouds with ragged deep convection near the center, so advisories were initiated on Tropical Depression 06E, located about 1100 nm east of the Hawaiian Islands or about 1500 nm west-southwest of Cabo San Lucas on the tip of the Baja California Peninsula. However, even as the depression was upgraded it was crossing the 25 C isotherm, so little further strengthening was forecast. The weak cyclone moved slowly north-northwestward and almost immediately ran into some southerly shear due to an upper-level trough lying to its west. By 1200 UTC on 23 August the depression consisted mainly of a swirl of low clouds with a few showers to the north and northeast of the center. Some intermittent bursts of convection were seen during the day as the trough, which although was the source of the shear, provided some diffluence over the system. By 24/0000 UTC the depression was beginning to dissipate with the center becoming elongated, resembling a shear axis. With strong shear still above the system and 24 C waters below, regeneration was deemed unlikely. The final advisory on TD-06E was issued at 0300 UTC and placed the disspiating center only about 200 nm north-northwest of its point of origin. Hurricane Flossie (TC-07E) 26 August - 2 September --------------------------- A. Origins ---------- The origin of Hurricane Flossie does not appear to be related to a tropical wave, but to a tropical LOW that was first noted off the Mexican coast on 24 August. The LOW tracked west-northwestward and steadily organized. By 0900 UTC on 26 August, its organization had increased enough to warrant its upgrade to Tropical Depression Seven-E approximately 175 nm south of Cabo San Lucas. The depression tracked roughly west-northwestward, south of a 500-mb ridge. It continued to strengthen, and was upgraded to Tropical Storm Flossie at 2100 UTC on the 26th, located 160 nm southwest of Cabo San Lucas. B. Track and Intensity History ------------------------------ Flossie intensified on the 27th under increasingly favorable conditions while its track bent more toward the west; this development spared it from cooler SSTs to its north. Satellite data supported its upgrade to Hurricane Flossie at 2100 UTC on 27 August about 310 nm west-southwest of Cabo San Lucas; this made it the first Pacific hurricane in over a month. Flossie made an unusual west-southwestward turn upon its upgrade, as the ridge to its north moved westward with it. On the 28th, Flossie tracked slowly southwestward, due to the strong ridge that was then to its northwest. The hurricane briefly became quasi-stationary late on the 28th; the ridge to its north weakened while a cyclonic shear axis to its southwest exerted a more northerly influence on the track. Another ridge southeast of Flossie placed the system in a weak col; even so, a slow northwestward track commenced late on the 28th as the northern ridge weakened. Flossie underwent a quick burst of intensification the following day, and peaked at 2100 UTC on 29 August some 445 nm west of Cabo San Lucas. At this time, it had an estimated MSW of 90 kts and a 972-mb CP. Flossie slowly weakened thereafter as it tracked over cooler SSTs. Flossie dropped below hurricane strength on the 31st; late that day its track turned to the north, then northwestward on the 1st as a shortwave trough "picked up" the system. The storm weakened to a depression at 1500 UTC on the 1st, due both to increased vertical shear and unfavorable SSTs. The final advisory on Tropical Depression Flossie was issued at 0300 UTC on 2 September, placing the dissipating center about 585 nm west-northwest of Cabo San Lucas, or roughly 200 nm west-southwest of Punta Eugenia. Moisture from Flossie's remnants spread across Baja California and the American Southwest, advected northeastward by upper-level winds. C. Meteorological Aspects ------------------------- Flossie was notable for both being the first storm after an unusually long break in Northeast Pacific activity, and for being an amazingly compact tropical cyclone. Upon its upgrade to a named storm, tropical storm-force winds extended only 50 nm from the center; the radii were never greater than 75 nm throughout its life. At its peak, hurricane-force wind radii were only 15 nm, as compared to the 15 nm-diameter of the eye itself. It has been hypothesized that Flossie's small size was the key to its surprising peak intensity, given its proximity to cool water and stable air; if it had been larger, it might have entrained more dry air or caused more upwelling. D. Damage and Casualties ------------------------ No casualties are known, and no watches or warnings were required. *********************************************************************** NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for August: 3 tropical depressions ** 3 tropical storms 2 typhoons 1 super typhoon ** - One of these was treated as a tropical depression only by PAGASA. Another was classified as a tropical depression by JMA, NMCC and Taiwan, but not by JTWC. The third was treated as a tropical depression by JMA and briefly by JTWC; Roger Edson, however, believes this system reached tropical storm intensity. NOTE: Most of the information on each cyclone's history presented in the narrative will be based upon JTWC's advisories, and references to winds should be understood as a 1-min avg MSW unless otherwise noted. However, in the accompanying tracking document I have made comparisons of coordinates with JMA (Japan) and the Philippines (PAGASA) when their positions differed from JTWC's by usually 40-50 nm or more. A special thanks to Michael V. Padua, owner of the Typhoon 2000 website, for sending me the PAGASA and JMA tracks. Also, some information based upon warnings issued by the National Meteorological Center of China (NMCC) and the Hong Kong Observatory (HKO) is included. The tracks from these agencies were sent to me by Huang Chunliang of Fuzhou City, China. Finally, Roger Edson of the University of Guam sent me his versions of tracks for Tropical Depression 15W and Tropical Depression Jolina. A special thanks to these gentlemen for the information they sent. In the title line for each storm I plan to reference all the cyclone names/numbers I have available: JTWC's depression number, the JMA-assigned name (if any), JMA's tropical storm numeric designator, and PAGASA's name for systems forming in or passing through their area of responsibility. Northwest Pacific Tropical Activity for August ---------------------------------------------- A very active August followed on the heels of an active July. Six named storms developed--one more than in July, but only three reached typhoon intensity--one less than in July. However, one of the August typhoons, Wutip, became the season's first super typhoon as winds climbed to 130 kts. (All these typhoon statistics are based upon JTWC's classifications.) None of the typhoons made landfall while at typhoon strength, although Typhoon Man-yi passed through the northernmost Marianas Islands. Typhoon Pabuk, after weakening to tropical storm strength, made landfall in south-central Honshu and skimmed eastward along the coast, passing very near Tokyo. Weak tropical storms Usagi and Fitow made landfall in Vietnam and southern China, respectively. Reports on all of the named cyclones follow. There were three systems (possibly four) which were classified as tropical depressions by one or more of the several TCWCs in the NWP basin. Following are brief synopses of these systems. Tropical Depression(s) of 2-3 and 6-8 August - A low-pressure area moved quickly westward from a position several hundred miles southeast of Okinawa. At 02/0000 UTC JMA referred to the system in their High Seas Warning and Summary bulletin as a weak tropical depression located about 525 nm southeast of Okinawa. By 1200 UTC the system had moved to a position about 300 nm south-southeast of Okinawa and JMA assessed the maximum winds to be 30 kts. The depression continued moving rapidly westward and by 0600 UTC on 3 August was located 150 nm southeast of Taipei, Taiwan. The system was also showing signs of weakening. It reached the coast of China near Fuzhou City around 1500 UTC the same day. JTWC did not classify this system as a tropical depression nor were any TCFA's issued; however, in addition to JMA, both NMCC and Taiwan's Central Weather Bureau treated the LOW as a depression. After moving inland the system turned more to the north, then east- ward after reaching Anhui Province. The depression's remnants passed near Shanghai on 5-6 August, triggering a 14-hour period of heavy rains which began around 1600 locally on the 5th. By 0800 (local) the next morning, the city had averaged 150 mm of rain with the Huangpu district netting 289 mm and several other districts, including Xuhui and Luwan, exceeding 220 mm. The rain was reported to be the heaviest that the Shanghai area had seen in ten years. Over 30,000 residential houses were inundated. Additionally, the system triggered a tornado which struck Sunqiao, Shanghai. At 0600 UTC on 6 August, JMA noted the existence of a weak tropical depression in the southern Yellow Sea about 100 nm north-northeast of Shanghai. JTWC also mentioned the disturbance in their STWOs, giving it a fair potential for development. The system, however, did not strengthen further, and after remaining quasi-stationary for a day or so, began to move off to the northeast and crossed the Korean Peninsula as a weak LOW. There is no conclusive evidence that this second system was a redevelopment of the depression of 2-3 August, but it does seem likely that they were related. (A special thanks to Huang Chunliang for sending me the information on the Shanghai rainfall event.) Tropical Depression Jolina - PAGASA issued bulletins on a South China Sea system on 16-19 August which was named Jolina. During this period the depression remained basically quasi-stationary west of Luzon. To my knowledge no other warning centers issued any bulletins on this system. After I had posted the August tropical cyclone tracks, I received some information from Roger Edson on circulations in the South China Sea. Roger wrote: "Active monsoon trough during this period with axis around 16N. Several circulations developed along the trough (at least one on the 13th and one on the 15th). Finally I could follow the third circulation from the 17th (Jolina) with good scatterometer and microwave data from this point. Nice exposed circulation on the 21st in the mid-South China Sea." Roger also sent his version of a track for Jolina. I have incorporated Roger's tracking information into the track for Jolina and have re-sent the August tracks file to the gentlemen who archive the summaries and tracks. Tropical Depression 15W - At 1200 UTC on 24 August, JMA noted in a High Seas Bulletin the existence of a weak tropical depression about 350 nm northwest of Wake Island. This system subsequently followed a long trajectory which took it generally northwestward to just east of the northernmost Japanese island of Hokkaido. It then recurved to the north-northeast and passed through the southern Kuril Islands as it became extratropical. JMA estimated that 30-kt winds were associated with the depression on 25 August, but for the remainder of its life it was relegated to the Summary portion of the bulletins, implying 25-kt winds. At 1800 UTC on the 24th JTWC issued the first of three warnings on the depression, numbering it TD-15W. The MSW was estimated at 30 kts and the system was forecast to strengthen to a tropical storm. However, the third warning (25/0600 UTC) indicated that the system was merging with a frontal boundary and dissipating. However, Roger Edson sent me his version of a track for this system and he feels that it reached tropical storm intensity. Roger does note that it was very difficult to follow, especially at first, as it was very small and mostly embedded in the monsoon trough. Roger feels that JTWC "lost" the system as it accelerated northward along the west side of the monsoon trough, with this beginning to happen overnight when there was no visible imagery. Roger's track for the system follows JMA's track fairly closely and starts the depression at 23/1800 UTC with tropical storm intensity being reached at 1200 UTC on the 24th. Roger estimates that a peak intensity of 50 kts was reached at 0600 UTC on 26 August when the system was located several hundred miles east-southeast of Tokyo. It is interesting to note that on 26 and 27 August, SAB was assigning CI numbers of 2.5 (35 kts) which lends support to the idea that the system did reach tropical storm intensity. In addition to the JMA/JTWC track for TD-15W, the cyclone tracks file for August contains Roger Edson's track for this system with several of his comments included in the remarks column. Typhoon Man-yi (TC-12W / TY 0109) 1 - 11 August ---------------------------------- Man-yi: contributed by Hong Kong, was originally the name of a strait. With the construction of a dam, that part of the sea has become a reservoir. A. Origins ---------- A STWO issued by JTWC at 0200 UTC on 31 July noted that an area of convection was developing approximately 150 nm north of Pohnpei. Animated infrared imagery showed persistent deep convection and cyclonic turning whereas animated visible imagery and synoptic data did not support the existence of a closed LLCC. A 200-mb analysis showed weak ridging over the disturbance. A few hours later microwave imagery depicted improving organization with weak low-level cloud lines indicative of a developing LLCC; the development potential was upgraded to fair. A TCFA was issued at 0100 UTC on 1 August. Convective organization was improving and a recent SSM/I pass had revealed a possible banding feature south of the LLCC. The system exhibited good outflow to the south and east. The STWO issued at 0600 UTC noted that there had been a new flare-up of deep convection near the center during the previous few hours. An upper-level LOW to the north was enhancing outflow, and water vapor imagery and a 200-mb analysis depicted organizing equatorial outflow to the south of the center. JTWC issued the first warning on TD-12W at 01/1800 UTC with the center located about 200 nm north-northeast of Chuuk, moving west-northwestward at 8 kts. On the second warning--issued at 02/0000 UTC---JTWC upgraded the depression to a tropical storm based on satellite CI estimates of 30 and 35 kts. Infrared satellite imagery depicted rapidly improving organization and banding over the past few hours. The storm continued moving to the northwest and steadily intensified. The MSW was upped to 45 kts at 0600 UTC based on CI estimates of 35 and 45 kts; satellite imagery revealed a developing 130-nm diameter CDO feature with cold cloud tops to -83 C. NMCC upgraded the system to a tropical storm at 0600 UTC, and JMA followed suit at 1200 UTC, naming the cyclone Tropical Storm Man-yi. At the time, Man-yi was centered approximately 300 nm north-northwest of Chuuk or about 325 nm east-southeast of Guam. B. Track and Intensity History ------------------------------ Initially, Tropical Storm Man-yi was steered northwestward or north- northwestward at a fairly good clip of around 15-16 kts by a low- to mid-level subtropical ridge to the storm's northeast. The cyclone steadily intensified, reaching typhoon intensity at 0600 UTC on the 3rd (per JTWC) when located about 125 nm east-northeast of Saipan. Winds had reached 95 kts by 04/0000 UTC--enhanced infrared imagery depicted deep convection developing in the eyewall. JTWC upped the MSW to 110 kts at 0600 UTC, noting that Man-yi was a symmetric system with a round eye 6 nm in diameter. Typhoon Man-yi reached an initial peak intensity of 115 kts at 1200 UTC on the 4th when satellite imagery revealed a well-defined primary banding feature wrapping in toward the vortex center from the southwest. Gales extended outward 145 nm northeast of the center and 60 nm to the southwest, while storm-force winds reached outward 75 nm to the northeast and 35 nm to the south- west. Man-yi was centered about 200 nm southeast of Iwo Jima at the time. As Man-yi continued north-northwestward it moved into a weakness in the subtropical ridge and recurved to the northeast on the 5th. The storm reached the westernmost point of its track at 05/0000 UTC when it was centered approximately 115 nm east of Iwo Jima. After recurving to the northeast, Man-yi initially weakened some with winds dropping to 95 kts by 06/0000 UTC. This weakening was likely due to some shear plus an eyewall replacement cycle. A 04/1102 UTC SSM/I pass depicted a collapsed eyewall in the eastern quadrant with an associated banding feature over the southwest quadrant; winds were lowered to 110 kts at 04/1200 UTC. At 06/0000 UTC water vapor imagery indicated less vertical shear over the typhoon with an outflow channel to the north. Man-yi responded by re-intensifying to 115 kts by 1200 UTC on the 6th. By this time the system had developed pronounced dual outflow channels, and the gale- and storm-force wind radii were more symmetric than at the earlier peak. Gales extended outward 110 nm northeast of the center and 90 nm to the southwest, while 50-kt winds reached out an estimated 60 nm to the northeast and 50 nm to the southwest. Man-yi's large 45-nm round eye was centered about 250 nm northeast of Iwo Jima at this time. As Typhoon Man-yi continued on toward the northeast, gradually curving back more to the north-northeast, it began to slowly weaken. The diameter of the eye also continued to increase, reaching 65 nm at 07/0000 UTC. The storm became one of the so-called truck-tire, or annular, typhoons: storms which develop a very large eye in proportion to the CDO and look like huge doughnuts or truck tires. Winds were down to 95 kts by 1800 UTC on 7 August and the storm was beginning to exhibit signs of extratropical transition. By the 8th Man-yi was north of the ridge axis and still moving northeastward, but a mid-level HIGH was forecast to move out of the Sea of Okhotsk and cause the storm to take a more northward track. This forecast verified--by 08/1200 UTC Man-yi was moving northward at 17 kts from a position about 550 nm east of Tokyo. Peak winds were down to minimal typhoon intensity and cold air was wrapping into the circulation from the north and west with no eyewall visible any longer. JTWC declared Man-yi to be extratropical at 1800 UTC on the 8th and issued their final warning, placing the storm about 500 nm south of the Kuril Islands. JMA continued to carry Man-yi as a tropical storm until 1800 UTC on 9 August when it was well east of Hokkaido. The extra- tropical remnants of Man-yi continued trekking northeastward parallel to the Kuril Island chain. By 11/0000 UTC the system had weakened to a 20-kt LOW southeast of the tip of the Kamchatka Peninsula. In summary, Typhoon Man-yi reached an estimated peak intensity (per JTWC) of 115 kts on three occasions: at 1200 and 1800 UTC on 4 August, at 0600 UTC on 5 August, and at 1200 and 1800 UTC on 6 August. The minimum central pressure assigned by JMA was 945 mb at 0000 and 0600 UTC on 5 August. C. Meteorological Aspects ------------------------- The most noteworthy event of Man-yi's history, meteorologically speaking, was the evolution of its eye from a pinhole eye only 6 nm in diameter on the 4th to a huge 65-nm diameter eye on the 7th. An eyewall replacement cycle seems to have been ongoing during part of this period. The JTWC warning issued at 05/0600 UTC noted that an apparent eyewall replacement cycle was beginning with visible imagery depicting a developing convective ring 33 nm in diameter. Six hours later the eyewall had collapsed in the eastern quadrant. The 1800 UTC warning noted that a TRMM pass at 1315 UTC had depicted a nearly concentric rainband outside a large eye feature. The diameter of the eye had grown to 45 nm at 06/0600 UTC and to 65 nm at 0000 UTC on the 7th. According to Mark Lander, once a tropical cyclone reaches this "annular" stage, the large eye condition tends to be stable. Also, Mark noted that this particular type of tropical cyclone evolution is fairly common in the region of the Ryukyu Islands--many typhoons with very large eyes have crossed Okinawa. Typhoon Man-yi was located not all that far from the primary "truck-tire" region. D. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in excellent agreement between the various warning agencies throughout the life of Man-yi. As usual, the intensity estimates between JTWC and JMA agreed fairly well during the earlier stages of the cyclone and during the weakening phase. JMA's peak 10-min mean sustained wind estimate was 80 kts from 04/1200 UTC through 06/0000 UTC, whereas, as noted above, JTWC's peak 1-min avg MSW estimate was 115 kts. JMA's reported intensities also do not show the double peak as indicated by JTWC: JMA's intensity estimates remained at 75 kts during the storm's second intensification phase reported by JTWC. NMCC's peak 10-min mean MSW was 100 kts from 04/1200 through 05/1200 UTC. This agrees very closely with JTWC's peak 1-min avg MSW of 115 kts; however, neither do NMCC's intensities reflect the second peak, remaining at 80 kts through this period. E. Damage and Casualties ------------------------ Typhoon Man-yi passed through the northernmost Marianas Islands on 3 and 4 August during the time at which it was becoming a rather intense typhoon; however, I have received no reports of any damage or casualties that might have resulted. If any become available later, they will be reported in a future summary. Tropical Storm Usagi (TC-13W / TS 0110) 8 - 11 August ---------------------------------------- Usagi: contributed by Japan, is the Japanese word for rabbit A. Origins ---------- A STWO issued by JTWC at 0600 UTC on 8 August mentioned that an area of convection had developed and persisted in the South China Sea just west of Luzon. Animated visible imagery depicted organized convection associated with a possible LLCC in a region of weak to moderate vertical shear. At 1800 UTC the disturbance was located approximately 330 nm south of Hong Kong with animated enhanced infrared imagery showing new deep convection developing west of the LLCC. JTWC upgraded the development potential to fair at this time. The first warning on TD-13W was issued at 09/0000 UTC with the center located about 300 nm south of Hong Kong. The MSW was estimated at 25 kts and the depression was moving west at 12 kts. (NOTE: The JMV file, a sort of working Best Track, indicates that JTWC retro- actively considers the system to have become a depression at 0600 UTC on 8 August about 400 nm south-southeast of Hong Kong.) The second warning (at 09/0600 UTC) noted that the center of TD-13W was fully- exposed about 30 nm east of the deep convection. Six hours later the center was still exposed but a weak banding feature was attempting to wrap into the vortex from the southwest. Upper-level easterlies of 30 to 40 kts over the region were continuing to hamper further development of the depression. Organization had improved slightly by 1800 UTC and JTWC increased the MSW to 30 kts. A SSM/I pass at 09/2240 UTC depicted a partially- exposed center with deep convection still sheared to the west; CI estimates had risen to 30 and 35 kts around this time. By 0600 UTC on the 10th animated visible imagery indicated that the LLCC was situated beneath the extreme northern edge of the deep convection. JTWC relocated the center to a position about 70 nm west of the previous warning position, just off the Vietnamese coast south- southwest of Hainan Dao. CI estimates were 35 kts and JTWC, NMCC and JMA all upgraded the system to a tropical storm with JMA assigning the name Usagi. Six hours later HKO had also upgraded Usagi to a 40-kt tropical storm. B. Track and Intensity History ------------------------------ Usagi's career as a tropical storm was quite short-lived, however. The storm reached its peak intensity of 40 kts (per JTWC) at 1200 UTC on the 10th when it was located about 80 nm east of the Vietnamese coast and moving westward at 11 kts. Enhanced infrared imagery showed a primary banding feature wrapping in toward the center from the south- west. By 1800 UTC the center had moved inland about 155 nm south of Hanoi and was weakening, so JTWC issued their final warning with Usagi continuing to move farther inland at 20 kts. Tropical Storm Usagi tracked westward throughout its life along a monsoon trough south of a weakening low- to mid-level ridge. There were some synoptic reports received of winds to 35 kts as the weak tropical storm made landfall. C. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in good agreement between the several warning centers throughout the life of Usagi despite the fact that the system remained weak. JMA's maximum 10-min avg MSW was 35 kts, which represents excellent agreement with JTWC's peak 1-min avg MSW of 40 kts. HKO and NMCC, however, reported a slightly stronger system with peak 10-min mean winds of 40 and 45 kts, respectively. D. Damage and Casualties ------------------------ I have been unable to locate any reports of damage or casualties resulting from the landfall of Tropical Storm Usagi in Vietnam. There was flooding reported in that country during the month of August, but I have found no press reports which link the flooding with Usagi. Typhoon Pabuk (TC-14W / TY 0111) 14 - 24 August --------------------------------- Pabuk: contributed by Laos, is the name of a large freshwater fish that lives in the Mekong River A. Origins ---------- JTWC issued a special STWO at 2100 UTC on 13 August for an area of convection about 130 nm north-northwest of Saipan which had developed rapidly over the previous 6-12 hours. Animated infrared satellite imagery depicted rapidly improving organization with a convective band developing south and east of a LLCC. Synoptic data indicated that the LLCC was located within a broad monsoon depression with 20-kt westerly winds south of the center and 25-30 kt winds east of the LLCC associated with some deep convection. Water vapor imagery and a 200-mb analysis indicated that an anticyclone was developing over the disturbance. Since the disturbance appeared to be rapidly developing and environmental conditions favored further strengthening, the development potential was immediately upgraded to good and a TCFA was issued shortly afterward. The first warning on TD-14W was issued at 14/0000 UTC placing the center 180 nm north of Saipan. CI estimates were 25 and 30 kts, and animated water vapor imagery indicated good outflow, particularly on the equatorward side. A 13/2012 UTC QuikScat pass showed a well- defined LLCC with extensive near-gale-force gradient westerlies south of the center. JTWC upgraded TD-14W to a tropical storm at 0600 UTC with the center located about 210 nm north of Saipan, moving north at 6 kts. JMA and NMCC upgraded the cyclone to a tropical storm six hours later with JMA assigning the name Pabuk. B. Track and Intensity History ------------------------------ Initially located in a region of weak steering between mid-level ridges to the north-northwest and east, Tropical Storm Pabuk moved slowly northward through the northernmost Marianas as a minimal tropical storm. At 14/1200 UTC the storm was relocated farther to the west along the western edge of the deep convection. Animated infrared imagery depicted deep convective bands south and east of the LLCC while animated multi-spectral imagery indicated that a broad circulation had not fully consolidated in the monsoon trough. A 14/0841 UTC QuikScat pass showed a LLCC with troughing to the west along the monsoonal axis. Water vapor imagery depicted good outflow equatorward of the center with strong upper-level westerlies to the north. At 15/0000 UTC the center was relocated 47 nm to the west of the previous warning position based on the appearance of a partially- exposed LLCC. The cyclone turned to a west-northwesterly track on 15 August as a ridge to the north strengthened. By 1200 UTC water vapor imagery and a 200-mb analysis indicated good outflow with the presence of a weak anticyclone aloft. Pabuk steadily intensified and reached typhoon intensity (per JTWC) at 1800 UTC on the 15th when it was centered about 425 nm northwest of Saipan. (NMCC upgraded the storm to a typhoon at 0600 UTC on 16 August while JMA waited until 1800 UTC to classify Pabuk as a typhoon.) According to JTWC Pabuk reached an initial peak intensity of 85 kts at 17/0000 UTC when the storm was centered about 575 nm northwest of Saipan. However, the storm began to show signs of weakening and JTWC lowered the MSW to 75 kts at 1200 UTC and to 70 kts at 1800 UTC. During this time Pabuk continued to track slowly west-northwestward in easterly flow south of the mid-level ridge to the north with some weak southerly flow generated by a ridge to the east-southeast. An upper-level shortwave trough over eastern China was forecast to move into the East China Sea and develop a weakness in the mid-level ridge over western Japan. By early on the 18th Pabuk was beginning to show signs of strengthening once more. The JTWC warning at 0600 UTC noted that a banding eye feature was visible in satellite imagery, and at 1200 UTC animated imagery depicted a developing eyewall with deep convection forming in all quadrants. Eyewall convection had improved by 1800 UTC and a 75-nm irregular eye was visible. Typhoon Pabuk reached its peak intensity of 95 kts at 0600 UTC on 19 August. Pabuk was a large storm, sporting an eye 50 nm in diameter with gales covering an area about 500 nm across; storm-force winds extended outward about 100 nm from the center. The 20/0000 UTC warning noted that the storm exhibited an irregular eye 55 nm in diameter with deep convection cycling diurnally. Animated water vapor imagery depicted excellent dual-channel outflow. On the 19th Pabuk began moving more northwestward toward a developing weakness in the ridge to the north, and by 1200 UTC on 20 August the storm was moving north-northeastward into a weakness created by a mid-latitude trough over the Sea of Japan. Winds were down to 80 kts by 1200 UTC; a SSM/I pass had revealed that most of the deep convective bands were in the northern semicircle and that the eyewall was eroding. Pabuk began to weaken rather rapidly as it approached the southern coast of Japan. The center of the cyclone just reached the coast of Japan on the southern tip of the peninsula south of Osaka around 21/1200 UTC with peak winds estimated at 55 kts. (JMA's 10-min avg MSW at the time was 60 kts.) The weakening storm turned more to the northeast and later east-northeast, skimming along the coast of southern Honshu. At 22/0600 UTC Pabuk's center passed just south of Tokyo and by 1200 UTC was back over the Pacific east of Honshu, moving east-northeastward at 19 kts and rapidly losing tropical characteristics. JTWC issued their final warning at 1800 UTC with the now-extratropical Pabuk located about 80 nm east-southeast of Misawa, Japan, and moving north-northeastward at 24 kts. The extratropical renmants of Pabuk continued moving northeastward and slowly weakened. By 24/1200 UTC the former tropical cyclone was a weak LOW in the western Bering Sea near the northeastern coast of the Kamchatka Peninsula. C. Meteorological Aspects ------------------------- At 21/0000 UTC Murotomisaki reported sustained 10-min mean winds of 60 kts with an attendant SLP of 976 mb. At the time of the observation, Pabuk's center was about 100 nm south-southeast of the station. Synoptic reports as the weakening cyclone approached and moved over coastal Honshu allowed forecasters to keep a good handle on the pressure. Synoptic reports around 21/0600 UTC indicated that the CP was around 970 mb. This had risen to 981 by 22/0000 UTC and to 988 mb at 1200 UTC after Pabuk had exited Japan and was back over Pacific waters. Per JTWC's warnings, Pabuk was at its peak intensity of 95 kts from 19/0600 through 20/0600 UTC. The minimum CP estimated by JMA was 955 mb at 17/0600 UTC, but then remained at 960 mb through 1200 UTC on the 20th. NOTE: After I had this report on Pabuk essentially written, I discovered in my files an e-mail from Julian Heming to Pete Donaldson which raises some questions about the intensity of the cyclone early in its life. JTWC initiated warnings on TD-14W at 14/0000 UTC and upgraded the depression to a tropical storm on the second warning at 0600 UTC. However, according to Julian's e-mail, ship WFLG reported winds of 40 kts at 13/1800 UTC, 39 kts at 13/2100 UTC, and a south wind of 46 kts at 14/0000 UTC. The ship's position was well south and east of JTWC's estimated center location, and it is possible that since Pabuk was developing as (or in) a large monsoon depression, JTWC did not consider the gale-force winds to be representative of the developing tropical cyclone's intensity. D. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in fairly good agreement between JTWC, NMCC and JMA during the life of Typhoon Pabuk. As noted above, JMA did not upgrade Pabuk to a typhoon until 24 hours after JTWC had done so; otherwise, intensity estimates were in fairly good agreement between the two warning centers. During Pabuk's initial peak of 85 kts, JMA's reported 10-min avg winds were around 70-75 kts, which represents very good agreement. However, JMA's intensity remained at 70 kts during the time Pabuk reached its peak JTWC intensity of 95 kts. The peak MSW (10-min avg) reported by NMCC was 80 kts for a full 3-1/2 day period, extending from 17/0000 through 20/1200 UTC. E. Damage and Casualties ------------------------ Pabuk moved through the Northern Marianas as a minimal tropical storm early in its career, but I have received no reports of damage of casualties from the islands as a result of the storm. Pabuk was responsible for seven deaths in Japan as it swept the southern coast of Honshu. Hundreds of homes were flooded and rail, sea, and air traffic were hampered. Super Typhoon Wutip (TC-16W / TY 0112) 26 August - 4 September --------------------------------------- Wutip: contributed by Macau, is the Macanese word for butterfly A. Origins ---------- An area of convection developed over the Philippine Sea west of Guam on 25 August; a STWO issued by JTWC at 0600 UTC noted that a weak LLCC with associated scattered deep convection lay within a broad monsoon circulation. A 200-mb analysis indicated weak to moderate vertical shear over the region. The system began to develop fairly quickly; the development potential was upgraded to fair at 26/0100 UTC, and a TCFA was issued at 0400 UTC, upgrading the potential for development to good. The disturbance was centered approximately 340 nm north- northwest of Guam at the time. Another 200-mb analysis indicated good diffluence aloft with a possible anticyclone forming over the area. Deep convection was scattered but improving in organization; moderate vertical shear was still inhibiting development somewhat. JTWC issued the first warning on TD-16W at 0000 UTC on the 27th, locating the center about 330 nm northwest of Guam. The initial MSW of 30 kts was based on CI estimates of 25, 30 and 35 kts. Organization had improved markedly over the past six hours with an increase in deep convection noted. (NOTE: The JMV file from JTWC classifies the system as a 25-kt tropical depression at 26/1800 UTC--six hours prior to the issuance of the first warning.) JTWC upgraded the depression to a tropical storm at 27/0600 UTC with the center located approximately 325 nm northwest of Saipan. The MSW was estimated at 35 kts--this was upped to 45 kts six hours later. Also at 1200 UTC, JMA upgraded the system to Tropical Storm Wutip with 40-kt winds (10-min avg), and NMCC also classified Wutip as a tropical storm at this time. B. Track and Intensity History ------------------------------ Throughout its life Wutip tracked generally northeastward along a reverse-oriented monsoon trough under the influence of a mid-level ridge to its southeast. Tropical Storm Wutip's intensification proceeded at a rapid pace. An eye feature was seen developing at 28/0000 UTC so JTWC upgraded Wutip to a typhoon only 18 hours after it had been declared a tropical storm. The fledgling typhoon was located slightly more than 100 nm west of the northernmost Marianas Islands at the time. By 0600 UTC a 12-nm irregular cloud-filled eye had become visible, and a 28/1055 UTC SSM/I pass depicted a primary banding feature wrapping in toward the vortex center from the north- west. The MSW was upped to 90 kts at 1200 UTC and to 115 kts at 1800 UTC when Wutip was centered about 250 nm southeast of the island of Iwo Jima. Continuing to the northeast, Wutip had reached a point about 250 nm east-southeast of Iwo Jima by 29/0600 UTC. Based on CI estimates of 127 and 140 kts, JTWC increased the MSW to 130 kts, making Wutip the first super typhoon of the year. The warning noted that interaction with an upper-level trough to the northwest had resulted in rapid intensification of the system. Gales covered an area 180 nm in diameter around a well-defined 10-nm round eye. The diameter of the area of 50-kt winds was 100 nm while the maximum radius of 100-kt winds was estimated at 25 nm. Wutip was maintained as a super typhoon for only six hours; at 1200 UTC all the CI numbers were 6.5 so the MSW was reduced to 125 kts. Typhoon Wutip's center passed about 300 nm due east of Iwo Jima at 29/1800 UTC. By 30/0000 UTC the storm displayed a 20-nm eye with warming cloud tops; however, one CI estimate of 140 kts was received so the MSW remained at 125 kts, but was lowered slightly to 120 kts six hours later. As Typhoon Wutip continued to move northeastward away from the tropics and into the subtropical zone, it began to weaken. At 1800 UTC on 31 August animated infrared imagery depicted a reduction in the coverage of deep convection; the intensity had been reduced to 75 kts by that time. The JTWC warning at 0000 UTC on 1 September noted that Wutip was beginning to enter the early stages of extratropical transition, although at 0600 UTC the storm still had a fairly well- defined banding eye feature with the MSW estimated to be 70 kts at the time. A SSM/I pass at 01/1004 UTC revealed that deep convection was confined to the eastern semicircle, and by 1800 UTC dry air entrainment into the western semicircle had led to further weakening. JTWC down- graded Wutip to a 60-kt tropical storm at this time with further weakening forecast. The center had become partially-exposed by 02/0000 UTC, and Wutip had become more-or-less completely extratropical by 1800 UTC. JTWC issued the final warning on the cyclone at 1800 UTC, placing the center almost 900 nm east of Tokyo. The remnants of Wutip continued moving northeastward as a slowly weakening extra- tropical gale. By 0600 UTC on 4 September the system, still producing winds to 35 kts, had crossed the Dateline well to the south of the westernmost Aleutian Islands. To summarize, Super Typhoon Wutip's peak intensity of 130 kts (per JTWC's warnings) was reached on 29 August at 0600 UTC. The MSW was estimated at 115 kts or greater from 28/1800 UTC through 30/1800 UTC. The minimum CP assigned by JMA was 930 mb from 29/1200 UTC through 30/0600 UTC. C. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in very good agreement between the various warning centers throughout the life of Wutip. Intensity estimates between JTWC and JMA agreed well during the earlier and latter stages of the storm's history. JMA's peak estimated 10-min avg wind was 90 kts from 29/1200 through 30/0600 UTC. This was slightly after the time of JTWC's peak of 130 kts (29/0600 UTC). A little surprisingly, NMCC's maximum 10-min avg MSW estimate was also only 90 kts--from 29/0600 through 30/1200 UTC. D. Damage and Casualties ------------------------ Around the time that Wutip was reaching typhoon intensity, it passed close enough to the Northern Marianas such that the outer fringes of the storm would have affected the islands. However, I have not received any reports of damage or casualties resulting from Wutip. If any become available later they will be reported in a future summary. Tropical Storm Sepat (TC-17W / TS 0113) 27 August - 1 September ---------------------------------------- Sepat: contributed by Malaysia, is the name of a freshwater fish often found in rivers and swampy areas with lots of weeds, and also in paddy fields A. Origins ---------- A very active and extensive monsoon trough covered most of the Western North Pacific in late August. Tropical Depression 15W as well as named storms Wutip, Sepat, and Fitow all had their origins as circulations in the trough. There were numerous circulations, ranging from small eddys with only one or two thunderstorms to the intense Super Typhoon Wutip. Tracing the origin of Tropical Storm Sepat using the daily STWOs issued by JTWC led to a long journey around the NWP basin. The discussion below is based on what I gleaned from the STWOs, using the "previously located near" coordinates to piece together the continuity from day to day. However, it seems fantastic that one single, weak LLCC could make such a tour of the Western Pacific for over a week, at times making a quantum leap of several hundred miles from one day to the next. Given the numerous circulations crawling around in the huge monsoon trough, which some meteorologists dubbed "a marvel of nature", it seems likely that there were flare-ups of convection here and there which may or may not always have been directly traceable to a flare-up seen the previous day. The STWO issued by JTWC at 0600 UTC on 19 August mentioned that an area of convection was developing very deep in the tropics roughly 100 nm south of Pohnpei. Bands of deep convection were forming south of a broad LLCC. A 200-mb analysis indicated 20 kts of easterly shear over the area. The STWO for 20/0600 UTC indicated that the area of convection was southwest of Chuuk--over 500 nm west of the previous day's position. The existence of a broad LLCC was supported by animated visible imagery and synoptic reports. At 0600 UTC on the 21st the area of convection was relocated about 350 nm to the west- northwest to a position south-southwest of Guam. Moderate to strong vertical shear overlay the disturbance. By 22/0600 UTC the disturbance had migrated east-northeastward to a point south-southeast of Guam. A 22/0000 UTC surface analysis had indicated a broad LLCC; however, a QuikScat pass had been unable to resolve a single circulation but rather had revealed multiple areas of turning within the monsoon trough. An interim STWO issued at 2000 UTC relocated the disturbance to a position farther north over the Northern Marianas. Synoptic data indicated that a weak LLCC had formed in the monsoon trough and appeared to be merging with a shear line extending northeastward from the islands. Several bursts of convection had been noted along the trough. At 0600 UTC on the 23rd the area of convection was relocated to a point a couple hundred miles east of the Marianas. The majority of the deep convection remained south of the LLCC in low-level convergent flow. The system remained quasi-stationary on the 24th, but by 0600 UTC on 25 August had again been repositioned a couple hundred miles to the east with little change in structure. At 0600 UTC on the 26th the disturbance was relocated about 400 nm to the east of the previous day's position. The LLCC was by then located about 1000 nm east of the Marianas and had moved into a region of favorable vertical shear. JTWC upgraded the development potential to fair. A TCFA was issued at 26/1700 UTC with the LLCC estimated to be about 225 nm west of Wake Island. Animated satellite imagery indicated a convective band forming southwest of the LLCC with improving overall organization noted. Vertical shear was weak and the system had good outflow aloft. JTWC issued the first warning on TD-17W at 27/0000 UTC with the center located about 250 nm northwest of Wake Island and moving north- northwestward at 14 kts. The initial MSW of 30 kts was based on CI estimates of 25 and 30 kts. JTWC upgraded the depression to a tropical storm at 1800 UTC when it was centered approximately 400 nm northwest of Wake Island and moving northward at 8 kts. Six hours later JMA upgraded the cyclone to Tropical Storm Sepat. JTWC upped the MSW to 45 kts (which turned out to be the peak intensity) at the same time based on CI estimates of 45 and 55 kts. Also, a recent QuikScat pass had shown uncontaminated winds of 40 kts. A 200-mb analysis indicated that Sepat was experiencing enhanced outflow due to a TUTT lying to the northwest. NMCC was the last warning agency to upgrade Sepat to tropical storm status--they did so at 0600 UTC on 28 August. B. Track and Intensity History ------------------------------ Tropical Storm Sepat tracked on a course just west of due north for its entire life span as a tropical cyclone. The storm was steered on its poleward course by a strong mid-level HIGH centered generally east- northeast of the cyclone. As noted above the maximum MSW assigned by JTWC was 45 kts, and the peak 10-min avg MSW estimated by JMA was 40 kts. At 28/0600 UTC satellite imagery revealed new deep convection building over the vortex center, but a 28/0915 UTC SSM/I pass depicted a significant decrease in overall coverage of convection, although low- level cloud lines were still well-defined. By 29/0000 UTC Sepat had moved to a position about 1000 nm west of Midway Island. A SSM/I pass at 28/2009 UTC revealed only scattered deep convection associated with the circulation. JTWC decreased the intensity to 35 kts at this time. By 1800 UTC Sepat was located approximately 1250 nm west-northwest of Midway and moving north-northwestward at 29 kts. The concurrent JTWC warning indicated that the storm was becoming extratropical. JTWC issued their final warning at 0000 UTC on the 30th with Sepat located about 870 nm east-southeast of Misawa, Japan. The initial warning estimated the MSW at 25 kts, but later receipt of QuikScat data indicating winds to 30 kts, and a ship report of 30 kts, led to the issuance of an amended warning raising the winds to 30 kts. However, Sepat was forecast to be completely extratropical in 12 hours, so JTWC did not issue any further warnings. JMA, however, maintained Sepat as a 40-kt tropical storm for another 30 hours as the system turned to the east-northeast and accelerated. JMA deemed Sepat to be extratropical at 31/1200 UTC, and the final reference to this system in JMA's High Seas Bulletins placed it near the Dateline south of the Aleutians at 0000 UTC on 1 September as a weakening gale. C. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in good agreement between JTWC, JMA and NMCC for Tropical Storm Sepat. And, as noted above, intensity estimates between JTWC and JMA were also in excellent agreement, although JMA carried the storm as a tropical entity for over a day longer than JTWC. NMCC's intensity estimates were the lower of the three TCWCs--Sepat was maintained as a minimal 35-kt tropical storm for the entire period in which NMCC issued warnings. D. Damage and Casualties ------------------------ Tropical Storm Sepat did not affect any populated areas, and no damage or casualties are known to have resulted from this tropical cyclone. Tropical Storm Fitow (TC-18W / TS 0114) 28 - 31 August ---------------------------------------- Fitow: contributed by the Federated States of Micronesia, is the Yapese name for a beautiful fragrant flower A. Origins ---------- The STWO issued by JTWC at 0600 UTC on 26 August noted that an area of convection had developed west of Luzon in the South China Sea. Synoptic data and satellite imagery indicated a broad LLCC within the monsoon trough. CIMSS shear products indicated moderate vertical shear over the region. Disturbed weather had persisted in the northern South China Sea for a good portion of the month of August. As noted in the introductory section on NWP activity for August, there was possibly a connection between the circulation(s) classified by PAGASA as Tropical Depression Jolina and the later Tropical Storm Fitow. By 0600 UTC on the 27th the system had drifted slightly to the west of the previous day's position. JTWC upgraded the development potential to fair since convection was increasing in organization near the LLCC. By 28/0600 UTC the LLCC was again farther to the west at a position about 300 nm south-southwest of Hong Kong. Animated visible imagery depicted a broad LLCC with associated cloudiness along the periphery of the system. Synoptic data also indicated monsoon depression characteristics. A 200-mb analysis revealed improving environmental conditions conducive to development. HKO was the first warning agency to issue warnings--at 28/1200 UTC they issued the first warning on a 25-kt depression located about 285 nm south-southwest of Hong Kong. JTWC issued a TCFA for the system at 0900 UTC on the 28th. JTWC issued the first warning on TD-18W at 29/0000 UTC, locating the center approximately 210 nm southwest of Hong Kong, moving west- northwestward at 7 kts. JMA and NMCC also classified the system as a tropical depression at 0000 UTC. By 1200 UTC the center of TD-18W was located over the northeastern coast of Hainan Dao. JTWC assessed the MSW to be 25 kts based on satellite intensity estimates and synoptic ship reports of 25 kts. The depression subsequently moved slowly westward across the northern portion of the island. By 0600 UTC on 30 August the depression's center was near the north- west coast of Hainan Dao, moving out into the Gulf of Tonkin. NMCC upgraded the system to a 35-kt tropical storm at this time with JTWC and HKO both upgrading the depression to a tropical storm at 1200 UTC. The center was by this time over the Gulf of Tonkin moving slowly northwestward. Convection associated with the LLCC had increased and there was good outflow to the south. Also, SSM/I and TRMM imagery revealed a more organized LLCC embedded in the convection. B. Track and Intensity History ------------------------------ By 1800 UTC Tropical Storm 18W had turned to a slow northward track toward the coast of China. JTWC estimated the MSW at 35 kts based on CI estimates of 35 and 45 kts. At 31/0000 UTC both JTWC and NMCC increased the intensity to 40 kts; also at 0000 UTC, JMA upgraded the system to a tropical storm, naming it Fitow. By 0600 UTC on the 31st, Tropical Storm Fitow's center was on the coast of China near Dongxing, moving north-northwestward at 6 kts. JTWC maintained 40 kts as the MSW based on satellite intensity estimates of 35 and 45 kts and a synoptic report of 40 kts from near the center. JMA, however, down- graded Fitow to a 30-kt depression at 0600 UTC. By 1200 UTC Fitow was inland and dissipating over southwestern China and all the other TCWCs downgraded the system to depression status. This was JTWC's final warning, but NMCC and HKO each issued one more bulletin on Fitow at 1800 UTC. C. Meteorological Aspects ------------------------- Huang Chunliang has sent me several meteorological observations from southern China. The depression's center first made landfall near Wenchang City in Hainan Province around 1130 UTC on 29 August. According to some information Chunliang received from NMCC, Fitow dropped in excess of 700 mm of rain at some location (site unknown) on the island of Hainan--a very rare occurrence. The storm's final landfall occurred just southwest of Beihai City (21.5N, 109.1E) around 31/0300 UTC. At 31/0000 UTC Beihai recorded a SLP of 988 mb with sustained winds (presumably a 10-min avg) of 23 kts, gusting to 37 kts. At 0600 UTC the station reported a SLP of 996 mb with mean winds of 17 kts, gusting to 47 kts. Dongfang City recorded 815.3 mm of rainfall during the 8-day period from 27/1700 UTC through 2000 UTC on 4 September. A location within Changjiang County recorded 831.1 mm during the 72-hour period ending at 0800 UTC on 31 August with 404 mm falling during a 12-hour period on the 30th. Several locations recorded rainfall amounts in excess of 400 mm in the 72 hours ending at 31/0800 UTC. Wenchang City on Hainan Dao recorded 245 mm in the 30 hours ending at 1400 UTC on 29 August. Several stations in the Hong Kong area reported winds gusting in excess of gale force on 28 and 29 August when the depression was nearest to Hong Kong. Some of these observations were: 44 kts at Cheung Chau, 41 kts at North Point, 52 kts at Tai Mo Shun, and 54 kts at Waglan Island. Sustained winds in general were well below gale force except at Tai Mo Shun where mean winds reached 34 kts. Several stations in the Hong Kong area neared or exceeded 200 mm of rainfall for storm totals with the highest being 255 mm at Sha Tin and 227 mm at Jordan Valley. More detailed information can be found in a storm report on Fitow located on HKO's website (see Section E below for the URL). D. Comparisons Between JTWC and Other Centers --------------------------------------------- Center position coordinates were in fairly good agreement between the several warning centers for Fitow, especially considering that it was a weak, disorganized system. Although JMA classified the cyclone as a tropical storm for only one warning cycle, the difference between it and the other TCWCs was only a matter of 5 kts--it just happened to involve that very arbitrary but very important threshold of 34 kts. NMCC was the first agency to upgrade the system to tropical storm status (at 30/0600 UTC), and JTWC and HKO did so six hours later. Twelve hours elapsed before JMA issued their only tropical storm warning on the system, officially naming it Fitow. The maximum intensity estimated for Fitow was 40 kts, from both JTWC (1-min avg) and NMCC (10-min avg); the peak 10-min mean winds reported by JMA and HKO remained at 35 kts. E. Damage and Casualties ------------------------ As of 31 August, total economic losses in Hainan were estimated at 1.367 billian yuan. Over two million residents of the province were seriously affected by the storm, 1300 houses were destroyed, 106.5 thousand hectares of farmland were badly stricken, and 26,700 head of livestock were reported dead. In Guangdong Province almost a million and a half residents were seriously affected with 2380 houses toppled. There were also four deaths reported in the province. In the Hong Kong area two persons drowned when they were swept away by waves. The Hong Kong Observatory has prepared a report on Tropical Storm Fitow which can be found at the following website: (A special thanks to Chunliang for sending me all the information on the effects of this tropical storm.) *********************************************************************** NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for August: No tropical cyclones *********************************************************************** SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E Activity for August: No tropical cyclones *********************************************************************** NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E Activity for August: No tropical cyclones *********************************************************************** NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E Activity for August: No tropical cyclones *********************************************************************** SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E Activity for August: No tropical cyclones *********************************************************************** EXTRA FEATURE In order to shorten the amount of typing in preparing the narrative material, I have been in the habit of freely using abbreviations and acronyms. I have tried to define most of these with the first usage in a given summary, but I may have missed one now and then. Most of these are probably understood by a majority of readers but perhaps a few aren't clear to some. To remedy this I developed a Glossary of Abbreviations and Acronyms which I first included in the July, 1998 summary. I don't normally include the Glossary in most months in order to help keep them from being too long. If anyone would like to receive a copy of the Glossary, please e-mail me and I'll be happy to send them a copy. *********************************************************************** AUTHOR'S NOTE: This summary should be considered a very preliminary overview of the tropical cyclones that occur in each month. The cyclone tracks (provided separately) will generally be based upon operational warnings issued by the various tropical cyclone warning centers. The information contained therein may differ somewhat from the tracking and intensity information obtained from a "best-track" file which is based on a detailed post-seasonal analysis of all available data. Information on where to find official "best-track" files from the various warning centers will be passed along from time to time. The track files are not being sent via e-mail. They can be retrieved in the following manner: (a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206] (b) Login as: anonymous (c) For a password use your e-mail address (d) Go to "data" subdirectory (Type: cd data) (e) Set file type to ASCII (Type: ascii) (f) Transfer file (Type: get remote_file_name local_file_name ) (The files will be named with an obvious nomenclature--using August as an example: aug01.tracks) (g) To exit FTP, type: quit Both the summaries and the track files are standard text files created in DOS editor. Download to disk and use a viewer such as Notepad or DOS editor to view the files. The first summary in this series covered the month of October, 1997. If anyone wishes to retrieve any of the previous summaries, they may be downloaded from the aforementioned FTP site at HRD. The summary files are catalogued with the nomenclature: aug01.sum, for example. Back issues can also be obtained from the following websites (courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael Pitt, and Rich Henning): OR * NOTE*: The URL for Michael V. Padua's Typhoon 2000 website has changed slightly once more. Another website where much information about tropical cyclones may be found is the website for the UK Meteorological Office. Their site contains a lot of statistical information about tropical cyclones globally on a monthly basis. The URL is: TROPICAL CYCLONE REPORTS AVAILABLE JTWC now has available on its website the complete Annual Tropical Cyclone Report (ATCR) for 2000 and a report on the 2000-2001 season in the Southern Hemisphere. ATCRs for earlier years are available also. The URL is: Also, TPC/NHC has available on its webpage nice "technicolor" tracking charts for the 2000 Atlantic and Eastern North Pacific tropical cyclones; also, preliminary storm reports for all the 2000 Atlantic and Eastern North Pacific cyclones are now available, as well as track charts and reports on storms from earlier years. The URL is: Prepared by: Gary Padgett E-mail: garyp@alaweb.com Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays) *********************************************************************** *********************************************************************** >> Typhoon2000.com