From: Gary Padgett To: Multiple recipients of list WX-TROPL Subject: SUMMARY: July Global TC Summary Date: Friday, August 14, 1998 9:49 AM MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY JULY, 1998 (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.) *********************************************************************** JULY HIGHLIGHTS --> Northwest Pacific season finally gets underway, but barely --> First Atlantic tropical storm of the year develops --> Northeast Pacific basin activity continues *********************************************************************** 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 have included a Glossary of Abbreviations and Acronyms following the Author's Note at the end of the summary. *********************************************************************** ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for July: 1 tropical storm 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. Tropical Storm Alex (TC #1) 27 July - 2 August ---------------------------- The season's first tropical storm (and depression) in the Atlantic basin developed from a strong tropical wave which left the African coast on 25 July. By late on the 26th the well-organized wave was south of the Cape Verde Islands moving west at about 13 kts. The first tropical depression advisory was issued by TPC/NHC at 1200 UTC on 27 Jul when the system was located about 250 nm south-southwest of the Cape Verdes. Ship reports, satellite imagery, and scatterometer winds all indicated a well-defined surface circulation. Initially the depression was still involved with the monsoonal flow and did not intensify very rapidly. Increasing convective organization was seen on 28 Jul and the system was upgraded to Tropical Storm Alex at 0000 UTC on 29 Jul. Alex intensified very slowly as it moved westward at a fairly good clip. At 29/1800 UTC a Naval Oceanographic Office drifting buoy located about 100 nm west-northwest of the center reported a 6-min avg wind of 31 kts and a pressure of 1013 mb. Alex appeared better organized on 30 Jul and winds were increased to 45 kts. Satellite imagery revealed a central area of intense convection with fairly symmetric outflow, although there was some south-southwesterly shear over the system. The storm's forward motion slowed somewhat on 31 Jul as the system began to encounter increasing shear. Convection would intermittently cover the center, but most of the time the center was exposed. Winds were decreased to minimal tropical storm strength of 35 kts at 1800 UTC on 31 Jul but were bumped back up to 45 kts twenty-four hours later after a reconnaissance flight on 1 Aug estimated surface winds of 45 kts with a central pressure of 1010 mb and ship FNPH reported gusts to near hurricane force north of the center. As Alex weakened it turned a bit more to the west-northwest. A reconnaissance flight early on 2 Aug found only 24-kt winds near the center but measured winds of 37 kts in a band 120 nm northeast of the storm's center. However, a later flight could not locate a definite surface circulation center so Alex was downgraded to a tropical disturbance at 2100 UTC on 2 Aug about 400 nm east-northeast of San Juan, Puerto Rico. The remnants of Alex persisted for a few days but never showed any significant signs of re-developing. Since Alex remained far from any populated areas, no deaths or damages are known to have resulted from this tropical cyclone. Tropical Storm Alex got the Atlantic tropical cyclone season off to a later start than average, but not unusally so. The last year in which the first named storm formed later than Alex was 1992, and that storm was the very destructive Hurricane Andrew. (Coincidentally, Alex is the replacement name for Andrew in the 6-year rotating list of Atlantic tropical cyclone names.) In each of the seasons from 1993-1997 the first named storm has made its appearance on or before 1 July. *********************************************************************** NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for July: 1 tropical storm 2 hurricanes 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. Tropical Storm Celia (TC-04E) 17 - 21 July ------------------------------ The Northeast Pacific's third tropical storm of the season developed from a large area of disturbed weather which passed just offshore of the southwestern Mexican coast on 16 July. This disturbance produced some locally heavy rains over adjacent coastal areas, but the author has not learned of any casualties or significant damage due to any flooding induced by the heavy rains. Early on 17 Jul the system began to develop rather rapidly. The first advisory issued by TPC/NHC at 1500 UTC directly upgraded the disturbance to Tropical Storm Celia based on a 45-kt wind report from ship KGTI. The low-level center was easily observed by the radar at Cuyutlan, Mexico. Celia at this time was located about 150 nm west-southwest of Manzanillo. MSW in Celia were further increased to 50 kts at 0300 UTC on 18 Jul based on a 17/1700 UTC report of 50-kt winds from ship 4XGX which was located about 90 nm northeast of the center. The discussion mentioned that Dvorak estimates were only 35 kts. Celia at this time was not very well-organized. The storm initially moved on a northwesterly trajectory but began to curve to a more west-northwesterly course as it passed south of the tip of Baja California. The center of the storm was observed by the Los Cabos radar as Celia passed about 120 nm south of Cabo San Lucas shortly after 0600 UTC on 18 Jul at its peak intensity of 50 kts and estimated central pressure of 1000 mb. The center of the circulation was embedded in a small but concentrated area of deep convection. Based on a cumulative wind distribution graphic on TPC/NHC's website, it is likely that gale-force winds occurred just offshore from the tip of the Baja peninsula. After passing south of Baja California Celia began to slowly weaken as it continued on a westerly track out into the Pacific. Cooler SSTs took their toll on the storm, although the weakening was slow to occur since the circulation had become quite well-organized. The storm was downgraded to a dissipating depression at 20/0600 UTC, and the final advisory was issued at 0000 UTC on 21 Jul with the center located about 600 nm west of Cabo San Lucas. Hurricane Darby (TC-05E) 23 July - 1 August ------------------------- The first advisory on a newly developing tropical cyclone was issued by TPC/NHC at 0600 UTC on 23 Jul with the depression centered about 625 nm south-southwest of Cabo San Lucas. Tropical Storm Darby was christened 12 hrs later with 40-kt winds. Throughout its life Darby moved on a fairly smooth west-northwesterly course which ultimately took it well to the north of the Hawaiian Islands. Hints of an eye began to appear early on 24 Jul and by afternoon a well-defined eye was noted in satellite imagery. Darby was upgraded to a hurricane at 24/1200 UTC when located about 650 nm southwest of Cabo San Lucas. Hurricane Darby intensified quite rapidly, reaching an estimated peak intensity of 105 kts by 25/0600 UTC. Minimum pressure was estimated to have been 960 mb. The hurricane weakened slightly early on 26 Jul, but by mid-day a large eye had reappeared. Darby had apparently been undergoing a concentric eyewall replacement cycle. As Darby continued moving farther to the west, its track paralleled the 25 deg C isotherm so the storm did not weaken as quickly as forecast--MSW remained at 100 kts through 28/0000 UTC. The hurricane crossed 140W and entered the Honolulu AOR around 0600 UTC on 29 Jul. Darby was a minimal hurricane by this time and was downgraded to a tropical storm on the next advisory from CPHC. The combination of cooler SSTs and increased vertical shear caused Darby to steadily weaken as it continued on its west-northwesterly track which carried it well to the north of Hawaii. The system was downgraded to a depression at 0600 UTC on 31 July about 350 nm north- east of Hilo, and the final advisory was issued at 0000 UTC on 1 Aug with the weak center about 250 nm north-northeast of Hilo. A weak residual LOW was followed for a couple of days to near 26N, 166W at 0600 UTC on 3 Aug but showed no signs of re-intensification. Hurricane Estelle (TC-06E) 29 July ---> --------------------------- Hurricane Estelle formed several hundred miles to the east of where Darby had developed, but followed a similar general west-northwesterly course out into the Central Pacific. The first advisory on Tropical Depression 06E was issued at 1800 UTC on 29 Jul with the system centered about 150 nm south-southwest of Acapulco. Tropical storm intensity was attained 12 hrs later about 275 nm south-southeast of Manzanillo, and Estelle was upgraded to a hurricane at 31/0600 UTC when the storm was located about 500 nm south of Mazatlan, Mexico. The TPC/NHC discussion at 0300 UTC noted that Estelle had a large circulation that featured a strong core of central convection with several rainbands containing convection of moderate intensity. The bulletin accompanying the 1500 UTC advisory mentioned that convective tops in the storm's central region were reaching -80 deg C. By 0000 UTC on 1 Aug Hurricane Estelle was passing about 450 nm south of Cabo San Lucas with MSW estimated at 75 kts. Although as of this writing Estelle has dissipated in the Central Pacific, since the storm reached its peak intensity after 1 Aug, further details of Estelle's history will be contained in the August summary. *********************************************************************** NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for July: 2 tropical depressions 1 tropical storm 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. Also, as announced earlier in a separate posting, a column of 10-min avg MSW is included--the values being obtained from either PAGASA's or JMA's advisories. A special thanks to Michael V. Padua, owner of the Typhoon '98 webpage, for sending me the PAGASA tracks. In the title line for each storm I plan to reference all the cyclone names/numbers I have available: JTWC's depression number and name (if any), JMA's tropical storm numeric designator, and PAGASA's name for systems forming in or passing through their area of responsibility. Tropical Depression Akang (TC-01W) 7 - 11 July ----------------------------------- The first tropical depression of 1998 was first identified by JTWC at 1200 UTC on 7 Jul about 400 nm east-southeast of Okinawa. The system moved erratically for a couple of days, and then followed a fairly smooth west-northwesterly trajectory which took it through the extreme southernmost Ryukyu Islands and into northern Taiwan. On 8 Jul PAGASA initiated bulletins on the depression and named it Akang. Tropical Depression Akang battled vertical wind shear throughout its life and never became very well-organized. By 09/0000 UTC most of the central convection had been sheared toward the southwest, leaving a completely exposed low-level center. The shear continued, causing the low-level circulation to become elongated. Akang limped ashore onto the northern tip of Taiwan near Taipei, and was dissipating by 0000 UTC on 11 Jul. MSW were estimated at 30 kts with an estimated minimum pressure of 1002 mb (from JMA's advisories). Tropical Storm Nichole (TC-02W / TS 9801) 8 - 12 July ------------------------------------------ The Northwest Pacific basin's first tropical storm of 1998 was named on 8 July, making this year the latest-beginning tropical storm season in that basin at least since 1959. (This bit of information came from Mark Lander of the University of Guam.) A tropical depression had formed in the northern South China Sea between China and northern Luzon by 08/0000 UTC. The first JTWC advisory placed the center about 250 nm east-southeast of Hong Kong. TD-02W drifted northward, becoming Tropical Storm Nichole at 1800 UTC. A small CDO had developed and outflow had increased on the southern side of the depression. Over the next couple of days Nichole appeared to describe a small clockwise loop just west of the southern tip of Taiwan. The JTWC advisory issued at 10/0300 UTC stated that local station information indicated a landfall on Taiwan had been made near 09/1740 UTC and that synoptic observations supported minimal tropical storm intensity at the time. Peak intensity of 45 kts (with an estimated minimum pressure of 998 mb) was reached about that time. Nichole was down- graded to a depression at 0600 UTC on 10 Jul as it drifted westward in the Taiwan Straits. During this time the system remained poorly organized with an exposed low-level center and limited convection sheared to the south side of the center. After 12/0600 UTC the weak depression turned northward and was dissipating inland over China by 1800 UTC. Tropical Depression (TC-03W) 24 - 27 July ----------------------------- This tropical depression was associated with what seems to have been a rather complex weather system east of Japan in late July. In fact, it might be more appropriate to say "depressions" since the circulation carried in JMA High Seas Forecasts on 24 and 25 July appears to have been a distinct center from that identified by JTWC as TD-03W beginning at 25/0000 UTC. The Significant Tropical Weather Advisory (STWA) issued at 25/0100 UTC mentioned a large gyre-like upper LOW off the east coast of Japan with numerous vorticity maxima in its periphery. Special attention was called to two distinct centers. One was a low-level circulation near 28N, 142E (about 200 nm north- northeast of Iwo Jima), and this appears to be the center that had been carried by JMA for about 24 hrs. The first JMA bulletin on that depression was issued at 0000 UTC on 24 Jul and placed the center about 300 nm east of Iwo Jima. It had moved generally in a northwesterly direction to the aforementioned coordinates. Maximum winds reported by JMA were 30 kts (10-min avg). The STWA mentioned that an area of deep convection might be wrapping around the periphery of the broad cyclonic circulation but that the convection was located over 80 nm from the exposed center. MSW was estimated to be only 15-20 kts with a central pressure of 1004 mb. The same STWA mentioned another area of convection near 26N, 149E which was associated with a rapidly developing circulation that was tracking toward the north. It was apparently this center that JTWC classified as TD-03W. The depression was located about 425 nm east- northeast of Iwo Jima at 25/0000 UTC and was moving north-northwestward at a fairly quick pace. The center that had been tracked by Japan on 24 Jul was followed to near 29N, 141E by 25/1200 UTC but was subsequently dropped from the High Seas Forecasts. TD-03W tracked northward east of Japan, passing about 250 nm east of Tokyo around 0300 on the 26th. By 1800 UTC on 25 Jul the low-level center had become exposed about 35 nm from the nearest convection. By 26/0000 UTC there was no deep convection remaining near the center. On 26 Jul the weakening depression turned to the north-northeast and accelerated away from Japan. The system had initially been forecast to reach tropical storm intensity, but the vertical shear it encountered thwarted any further strengthening. *********************************************************************** NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for July: No tropical cyclones Additional Information on Arabian Sea Cyclone (TC-03A) 4 - 9 June --------------------------------------------- The author has uncovered a little more information on the effects of the deadly Arabian Sea cyclone (TC-03A) which devastated the coast of northwestern India in early June. The source for this was the website of the UN Office for the Coordination of Humanitarian Affairs (OCHA) - . According to this report (dated 19 Jun 1998), 1126 bodies had been recovered but the death toll could be as high as 3000 in the Kutch-Saurashtra region of Gujurat. About 1745 persons were still missing and 893 were reported injured. The number of houses/huts damaged was put at 158,000 and financial loss was estimated at Rs. 120 billion (about 3.01 billion U.S. dollars). In addition, in Rajasthan District, 11 persons died and 14,603 houses/ huts were damaged. *********************************************************************** SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E Activity for July: 1 tropical depression NOTE: The information presented below was gleaned from releases by the La Reunion TCWC, which is the WMO's Regional Specialized Meteor- ological Centre (RSMC) for the South Indian Ocean; and also from warnings issued by JTWC. References to sustained winds imply a 10-min averaging period unless otherwise stated. A special thanks to Alain Soulan and Paul Remois for passing along some information on nomenclature and warning practice in this basin. Tropical Depression "H4" (TC-01S) 20 - 25 July ---------------------------------- First, a few comments about cyclone nomenclature and classification in the South Indian basin: (1) La Reunion utilizes a more rigid and restrictive definition of the term "tropical depression" than do most TCWC's. To be classed as a tropical depression a disturbance must be adjudged to have a 10-min MSW of at least 28 kts (i.e., Beaufort force 7). Weaker systems for which advisories are issued are called "tropical disturbances". (2) In the South Indian basin the term "tropical cyclone" is reserved for systems which reach a 10-min MSW of 64 kts--hurricane force. Depressions are named when 10-min MSW exceed 34 kts and are called "tropical storms", as in U.S. and Japanese usage. When MSW exceed 47 kts (storm force) the system is called a "severe tropical storm". (3) Whenever a tropical disturbance has become sufficiently organized to warrant advisories being issued, the disturbance is given a two-character designator. The first character is the initial letter of the next cyclone name on the annual list (in this case, Hillary). The second character is a digit which is a sequential count of significant disturbances occurring since the last storm was named. Thus, "H4" was the fourth disturbance occurring since Tropical Storm Gemma was named in April, but was the first of these to reach tropical depression intensity. (4) In the South Indian basin the tropical cyclone season is considered to run from 1 Aug to 31 Jul instead of from 1 Jul to 30 Jun, as is the case with Australia and Fiji. But JTWC's numbering scheme for Southern Hemisphere tropical depressions and cyclones starts anew on 1 Jul each year; hence, this depression was considered by JTWC to be the first of the 1998/99 season while La Reunion will regard it as the last one of the 1997/98 season. The first advisory by La Reunion was issued at 0600 UTC on 20 Jul with the disturbance centered about 800 nm east of Diego Garcia. The system moved rather slowly toward the west-southwest for a couple of days. It was upgraded to a tropical depression with 30-kt MSW at 0600 UTC on 22 Jul. The center was estimated to be about 400 nm east-southeast of Diego Garcia at this time. By 23/0000 UTC the system was showing signs of weakening and was downgraded to a tropical disturbance. Interestingly, it wasn't until 0600 UTC on the 23rd that JTWC issued its first advisory, placing the depression center about 300 nm southeast of Diego Garcia. La Reunion dropped the system 6 hrs later, but JTWC continued issuing advisories until 25/0000 UTC. During this period the center stalled and began to drift northward and then to the east- northeast. The final advisory located the center about 300 nm east- southeast of Diego Garcia. This depression experienced considerable vertical shear throughout its life. At 1800 UTC on 21 Jul the system exhibited an exposed center with the nearest organized convection about 60 nm distant. By early on the 23rd the shear had abated somewhat and the low-level circulation appeared to be better organized. Given the proximity to Diego Garcia and the slight possibility that the system might reach tropical storm strength, JTWC decided to initiate advisories. *********************************************************************** AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E Activity for July: No tropical cyclones *********************************************************************** SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E Activity for July: No tropical cyclones *********************************************************************** 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) The files will be named with an obvious nomenclature--using July as an example: jul98.tracks 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 July summary is the tenth cyclone summary in this series; the first one covering the month of October, 1997. If anyone did not receive any of the previous summaries, they may be downloaded from the aforementioned FTP site at HRD. The summary files are catalogued with the nomenclature: oct97.sum, for example. Back issues can also be obtained from the following websites (courtesy of Michael Bath and Michael V. Padua): (since January only) The preliminary storm reports for all the 1997 Atlantic and Eastern North Pacific tropical cyclones are available on the Tropical Prediction Center's website: . These reports include the analyzed best-track for each cyclone. The staff of JTWC is also working on an on-line version of their Annual Tropical Cyclone Report for 1997. It is still under construction, but the best-track files are already available for 1997 Northwestern Pacific and North Indian Ocean cyclones. The URL is: Prepared by: Gary Padgett E-mail: garyp@alaweb.com Phone: 334-222-5327 *********************************************************************** GLOSSARY of ABBREVIATIONS and ACRONYMS AOML/HRD - Atlantic Oceanographic and Meteorological Laboratory/ Hurricane Research Division, located on Virginia Key, Miami, Florida, U.S.A. AOR - area of responsibility CDO - central dense overcast CPHC - Central Pacific Hurricane Center, Honolulu, Hawaii, U.S.A. FLW - flight level winds FTP - file transfer protocol IMD - India Meteorological Department (RSMC New Delhi, India) JMA - Japanese Meteorological Agency (RSMC Tokyo, Japan) JTWC - Joint Typhoon Warning Center, Guam kt - knot = 1 nautical mile per hour m - meter, or metre mb - millibar, numerically equivalent to hectopascal mm - millimeter MSW - maximum sustained wind(s) (either 1-min avg or 10-min avg) nm - nautical mile = 6076.12 feet or 1852.0 meters NPMOC - Naval Pacific Meteorological and Oceanographic Center, Pearl Harbor, Hawaii, U.S.A. PAGASA - Philippines' Atmospheric, Geophysical & Astronomical Services Administration RSMC - Regional Specialized Meteorological Centre SST - sea surface temperature STS - severe tropical storm (MSW greater than 47 kts) TC - tropical cyclone TCWC - Tropical Cyclone Warning Centre (generic term) TD - tropical depression TPC/NHC - Tropical Prediction Center/National Hurricane Center, Miami, Florida, U.S.A. TS - tropical storm WMO - World Meteorological Organization, headquartered at Geneva, Switzerland UTC - Universal Time Coordinated, equivalent to Greenwich Mean Time or Zulu (Z) *********************************************************************** *********************************************************************** +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from WX-TROPL send e-mail to LISTSERV@PO.UIUC.EDU with "unsub wx-tropl" in the body of your message. For help with the WX-TROPL or WX-TALK discussion groups write to chris@siu.edu or see http://www.inlink.com/~landmb/intro.html. For more information on tropical weather products, see the NCEP Products Homepage at http://www.nhc.noaa.gov/nhcprod.html.