From: Gary Padgett To: Multiple recipients of list WX-TROPL Subject: SUMMARY: April Tropical Cyclone Summary Date: Tuesday, May 12, 1998 9:47 AM MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY APRIL, 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.) SPECIAL NOTE to users of the TRACK FILES: I am going to make a slight change in the manner in which I handle intermonthly cyclones in order to minimize the number of track files that cover only a portion of a cyclone's life span. For cyclones forming late in a given calendar month and that do not cause any significant effects in the month of formation, the narrative will contain a reference to the system but the track file will be contained in the summary for the concluding month. For storms which carry over into the new month for only a few days and (especially) for which I have the complete tracking information already in hand when I prepare the summary for the previous month, I shall include the track file in the summary for the month of formation (e.g., Tropical Cyclone Bart). Cyclones whose history is split fairly evenly between two months and which are either intense or else cause significant effects in the month of formation I'll treat as I have previously done--ending the track abruptly at 0000 UTC on the first day of the second month and picking up the narrative at that point in the concluding month's summary. However, in these cases (as in previous summaries) the track file in the second month's summary will cover the entire history of the cyclone. *********************************************************************** EXTRA FEATURE: NORTHERN HEMISPHERE CYCLONE NAMES for 1998 The official Eastern North Pacific hurricane season will begin on 15 May, and the Atlantic and Central North Pacific official seasons begin on 1 June. The tropical cyclone season in the Western North Pacific basin is more or less a year-round affair, but no storms have been named so far this year, which is a little unusual. Following are the 1998 names for tropical cyclones forming in these basins: Atlantic - Alex, Bonnie, Charley, Danielle, Earl, Frances, Georges, Hermine, Ivan, Jeanne, Karl, Lisa, Mitch, Nicole, Otto, Paula, Richard, Shary, Tomas, Virginie, Walter Eastern North Pacific - Agatha, Blas, Celia, Darby, Estelle, Frank, Georgette, Howard, Isis, Javier, Kay, Lester, Madeline, Newton, Orlene, Paine, Roslyn, Seymour, Tina, Virgil, Winifred, Xavier, Yolanda, Zeke Central North Pacific - Upana, Wene, Alika, Ele, Huko, Ioke, Kika, Lana Western North Pacific - Nichole, Otto, Penny, Rex, Stella, Todd, Vicki, Waldo, Yanni, Zeb, Alex, Babs, Chip, Dawn, Elvis, Faith, Gil, Hilda, Iris, Jacob, Kate, Leo, Maggie, Neil, Olga, Paul, Rachel, Sam, Tanya, Virgil, Wendy, York, Zia, Ann, Bart, Cam, Dan, Eve, Frankie, Gloria *********************************************************************** ADDITIONAL INFORMATION for March Cyclone Summary When preparing the March summary I inadvertently overlooked some information I'd saved on a tropical LOW in the Gulf of Carpentaria in early March. I was able to gather some more information on this LOW from Sam Cleland of the Darwin TCWC. (Thanks to Sam for passing along the additional data.) This LOW appeared to be a surface reflection of the residual mid- level center of Tropical Cyclone May in late February. May had made landfall in the southern Gulf of Carpentaria region on 26 Feb and the remnants persisted over land for a few days. Shear separated the lower-level circulation from the mid- and upper-level portion of the circulation. The weak surface LOW that broke away dissipated rapidly, but the mid-level circulation spun down to the surface and a new LOW formed. JTWC issued a formation alert on this LOW but no warnings were subsequently issued. Darwin TCWC did issue some gale warnings on this system between 2300 UTC on 2 Mar and 0000 UTC on 4 Mar. The LOW remained quasi- stationary during this time in the general vicinity of 16.5S, 139E in the extreme south-central Gulf of Carpentaria. The LOW was forecast to cause monsoon gales of 30 to 40 kts in the eastern semi- circle and central pressure was initially estimated at 998 mb. By 04/0000 UTC winds had abated and the final advice was issued. No track is given for this system in the accompanying cyclone track file. *********************************************************************** APRIL HIGHLIGHTS --> Vanuatu suffers significant cyclone damage early in month --> French Polynesia once again experiences cyclone damage *********************************************************************** ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for April: 1 possible subtropical storm A Possible Subtropical Storm -- Early April ------------------------------------------- At 1400 UTC on 2 Apr the Tropical Prediction Center/National Hurricane Center in Miami, FL, issued a Special Tropical Disturbance Statement on a non-tropical area of low pressure located in the western Atlantic Ocean about 700 nm northeast of Puerto Rico. This system had been moving slowly northward for a couple of days, and had developed some organized central convection and was producing gale-force winds of 35-45 kts. The statement mentioned that although the LOW had taken on some tropical characteristics, it was still somewhat disorganized. It was forecast to begin moving to the northeast and become absorbed by a cold front over the next few days. By 0700 UTC on 3 Apr the LOW had moved northward to a position about 525 nm southeast of Bermuda, and the Tropical Weather Discussion issued at that time indicated that the gale center was weakening and there was little convection near the center. According to Dr. Jack Beven of TPC/TAFB, data on this system will be reviewed later to see if the system qualifies as a subtropical cyclone. HISTORICAL SIDELIGHT: Out-of-season tropical cyclones are very rare in the Atlantic basin, but a few have occurred; and the general region to the northeast of the Puerto Rico area and southeast of Bermuda could be considered a "hot spot" of sorts for the formation of tropical and subtropical cyclones between December and May. Some systems forming in this general vicinity during the off-season months include: (1) A hurricane in March, 1908--struck the Leeward Islands (2) Hurricane Able in May, 1951--brushed the northern Bahamas and east coast of Florida (3) An unnamed tropical storm in Dec, 1953 (4) Hurricane Alice in Dec, 1954-Jan, 1955--struck the Leeward Islands (5) A subtropical storm in Jan, 1978 (6) Hurricane Lili in Dec, 1984--briefly threatened the Leeward Islands (7) A subtropical storm in Apr, 1992 *********************************************************************** NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for April: No tropical cyclones *********************************************************************** NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for April: No tropical cyclones *********************************************************************** NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for April: No tropical cyclones *********************************************************************** SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E Activity for April: 1 tropical depression 1 tropical cyclone of gale intensity 1 tropical cyclone of hurricane intensity NOTE: The only sources of information on South Indian cyclones I have available for the time being are the warnings issued by JTWC. All the winds reported in the narrative are 1-min average maximum sustained winds. Tropical Cyclone Gemma (TC-32S) 7-15 April -------------------------------------------- The Joint Typhoon Warning Center (JTWC) on Guam issued the first warning on a developing tropical depression at 0000 UTC on 7 Apr with the circulation centered about 400 nm south-southwest of Diego Garcia. Maximum sustained winds were estimated at 30 kts. At the same time the first warning was issued on another depression (TC-33S) located about 300 nm to the east-southeast. TC-32S moved very slowly east- northeastward while TC-33S moved northwestward. By 07/1200 UTC the two depressions had merged, resulting in a broad and weak wind field. Following this merger TC-32S began to steadily intensify as it drifted westward. By 0000 UTC on 9 Apr the cyclone had been christened Gemma by the Mauritius Meteorological Service and was located about 400 nm southwest of Diego Garcia. Winds had increased to 55 kts and the system halted its westward motion and began to move on an east- southeasterly course. Gemma reached peak intensity at 11/0000 UTC when winds were estimated to have reached 70 kts; however, the cyclone began to weaken after this point as it moved slowly to the east-northeast. An amended warning at 11/0600 UTC, issued after visible imagery had become available, indicated that shear had begun to separate the upper-level convection from the low-level center. Microwave imager data on 12 Apr indicated that the low-level features remained well-defined and tightly wrapped in spite of the shear. By 0000 UTC on 13 Apr the weakening Gemma was located about 550 nm southeast of Diego Garcia with winds down to 45 kts. The cyclone then began moving westward once more as it continued to weaken. By 14/1200 UTC the low-level circulation center had become completely separated from the convection, but satellite imagery indicated that gale-force winds were still possibly occurring to the south and east of the center. The last JTWC warning at 0000 UTC on 15 Apr placed the center of the weakening depression about 450 nm south-southeast of Diego Garcia and only about 230 nm east of its point of origin. Tropical Cyclone 33S 7 April ------------------------------ The first warning on TC-33S, issued by JTWC at 0000 UTC on 7 Apr, located the system about 600 nm south-southeast of Diego Garcia and about 300 nm east-southeast of another developing depression: TC-32S. TC-33S moved generally on a northwesterly course while TC-32S drifted eastward. By 07/1200 UTC the estimated center of TC-33S was only about 140 nm east-southeast of TC-32S and the two depressions were merging into one system which was subsequently referred to as TC-32S. Maximum sustained winds in TC-33S were estimated at 30 kts. Tropical Cyclone 34S 19-22 April ---------------------------------- TC-34S was a relatively weak cyclone that never exceeded gale intensity. It was considered only a depression by the Southwest Indian meteorological services and never named. The first JTWC warning placed the system about 225 nm southeast of Diego Garcia at 0000 UTC on 19 April with 40-kt winds. The cyclone was expected to increase to hurricane force but persistent vertical shear prevented this from occurring. TC-34S moved generally on a westerly course throughout its life. Maximum sustained winds of 40 kts were estimated to have occurred on 19 and 20 April. A scatterometer pass at 21/0647 UTC indicated a lessening in the organization and in the radial extent of the surface wind field, and microwave imager data at 0000 UTC on 22 Apr indicated that the low- level circulation center was becoming elongated and the system was weakening. The last warning at 22/1200 UTC downgraded the cyclone to a depression about 200 nm east-southeast of Agalega in the western South Indian Ocean. *********************************************************************** AUSTRALIAN REGION (AUS) - From Longitude 90E Eastward to Longitude 160E Activity for April: 1 tropical depression ** ** - One warning was issued by JTWC classifying this tropical LOW as minimal tropical cyclone with 35-kt winds (1-min average) NOTE: Some of the material presented on Tropical Cyclone 35S is taken from the April Darwin Tropical Diagnostic Statement. Thanks to Lori Chappel for sending that report to me. Unless stated other- wise, references to sustained winds imply a 10-min averaging period. Tropical LOW (TC-35S) 19 April -------------------------------- TC-35S was a short-lived system along the North Kimberley coast of Western Australia. A LOW developed in the eastern Arafura Sea on 16 Apr as an easterly surge across Australia induced vorticity in the weak monsoon trough. An easterly wave may have also contributed to enhanced convection and low-level development. The LOW moved westward through the Arafura Sea and into the Timor Sea. On the 18th the LOW took a more southwesterly or south-southwesterly track. There was little convection near the center with some rainbands displaying slightly more organization than the day before. Locating the center was made difficult by various mesoscale vortices springing up within the larger circulation. During the night of 18 Apr a huge area of convection developed south of the estimated surface position. Organization had increased rapidly by 1800 UTC with good outflow channels displayed in the cirrus. Ship reports, however, supported locating the surface center much farther north. At 0000 UTC on 19 Apr JTWC issued the first warning on the system, locating it near the Western Australian coast about 300 nm northeast of Broome. Coincident with the convection mentioned previously Troughton Island (WMO 94102) reported a one hour period of gale-force winds reaching a peak sustained wind of 48 kts. This was believed to have been due to convergence in the rain band. Also, a bulletin from the Darwin TCWC at 19/0730 UTC indicated that wind gusts to 50 kts were being reported in rain squalls. Early morning visible images revealed the LOW was farther south and was experiencing some shearing. The low-level center could have been translated under the influence of the overnight convection, or there could have been two centers with the southernmost one becoming predominant. During the 19th the LOW continued to move farther south and inland and therefore did not strengthen further. *********************************************************************** SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E Activity for April: 2 tropical cyclones of gale intensity 1 tropical cyclone of hurricane intensity NOTE: Thanks to Steve Ready of the New Zealand Meteorological Service at Wellington for passing along some information on Tropical Cyclone Zuman. Unless stated otherwise, references to sustained winds imply a 10-min averaging period. Tropical Cyclone Zuman (TC-31P) 29 March-6 April -------------------------------------------------- As the month of April opened Tropical Cyclone Zuman had just crossed over the northern end of the island of Espiritu Santo, the northernmost island of Vanuatu. At 0000 UTC on 1 Apr the cyclone was centered about 175 nm north-northwest of Port Vila with maximum sustained winds estimated at 80 kts. Zuman may have weakened slightly after crossing the island but soon recovered from the effects of having been over land. Winds remained near 80 kts through 03/0000 UTC as the cyclone moved on a fairly slow track to the west. The westward motion halted about this time with the storm centered about 450 nm north-northwest of Noumea, New Caledonia. Minimum central pressure in the cyclone's history was estimated at 955 mb. Zuman then drifted to the south, and then began to slowly accelerate in a southeasterly direction while slowly weakening due to increasing shear. The cyclone brushed the entire eastern coast of New Caledonia, passing between that island and the Loyalty Islands on the 5th. Reports from ship ELH25 were useful in helping to locate the low-level circulation center late on 5 April. The center of Zuman passed a little less than 100 nm east of Noumea at 1800 UTC on the 5th. Winds had decreased to about 40 kts by this time and the last warning from Fiji, downgrading Zuman to a depression, was issued just 6 hrs later. The remains of the original vortex induced a depression along a cloudband (referred to by Steve Ready as a "son or daughter" of Zuman) which was tracked as an extension of Zuman. This secondary system produced several short bursts of heavy rain in the far northern and northeastern parts of New Zealand's North Island before slipping away toward the Chatham Islands and eventually into the higher latitudes of the South Pacific Ocean. This phase of the cyclone did not produce any winds of consequence. The island of Espiritu Santo sustained heavy damage due to Zuman with the eastern and northeastern parts of the island affected most severely. The most serious damage was to dwellings and coconut trees, seriously affecting the island's major industry, copra. All semi- permanent houses in Hog Harbour were partly or completely destroyed. Other towns hard hit were Port Olry and Luganville. Fortunately, no reports of fatalities have been received as of the time of this writing. If more information on Zuman's effects becomes available later it will be included in next month's summary. Tropical Cyclone Alan (TC-36P) 19-26 April -------------------------------------------- Tropical Cyclone Alan was yet another in the parade of tropical cyclones which have formed well to the east of the dateline in this strong El Nino season. A tropical disturbance had been tracked since 17/1800 UTC east of the Northern Cooks, and the Fiji Tropical Cyclone Warning Centre at Nadi issued the first bulletin on a new depression at 0600 UTC on 19 Apr with the weak center placed about 300 nm southeast of Manihiki Atoll in the Northern Cooks. The depression organized very slowly over the next several days while remaining in the same general area. When the advisory upgrading the system to Tropical Cyclone Alan was issued at 1800 UTC on 21 Apr, the center was located somewhat to the north of its original location, being about 150 nm east-southeast of Manihiki. Alan remained a weak, minimal tropical cyclone and meandered about slowly in the same area for a couple of days. Fiji downgraded Alan to a tropical depression at 1200 UTC on 23 Apr. The center was then only about 80 nm south of the location where it had been when it was named. The Naval Pacific Meteorological and Oceanographic Center (NPMOC) at Pearl Harbor issued one more warning at 1800 UTC and then dropped the system. Over the next 24 hrs the system appeared to become better organized and warnings were resumed on the 24th--at 1200 UTC by NPMOC and at 2100 UTC by Nadi. Alan had by this time begun to move at an increased pace to the east-southeast and was located about 300 nm west-northwest of Tahiti at 24/2100 UTC. Of the previous cyclones in this area during the current season, Alan's track most closely matched that of Tropical Cyclone Osea back in November. Alan moved very near or over the Society Islands of Maupiti, Bora-Bora, and Raiatea--islands which were heavily damaged by TC Osea. Maximum winds during this stage of Alan were estimated at 40 kts. The advisory at 1200 UTC on 25 Apr placed Alan about 125 nm west of Tahiti, but six hours later, after visible imagery was received, the center was re-located about 135 nm northwest of the 25/1200 UTC position. The 1800 UTC advisory also downgraded Alan back to a tropical depression. The weakening system continued to drift generally to the east-southeast, with the last advisory (at 26/1800 UTC) locating the system about 100 nm west-northwest of Tahiti. The remnants of the former cyclone remained in the area west of Tahiti for several days. Although weak and diffuse, Alan was not without casualties. The author has received reports of 8 fatalities caused by the storm, mostly due to mudslides caused by the attendant torrential rains. One report mentioned 6 deaths on the island of Tahaa which had winds gusting to 50 kts. (I have been unable to locate this island on a map, but presumably it is in the vicinity of the other islands mentioned above.) If any more information on the effects of TC Alan becomes available, it will be reported in the next summary. NOTE: This cyclone was accidentally numbered as TC-32P by NPMOC when the first warning was issued. In order to avoid confusion this number was used operationally thoughout the cyclone's life, but it will be officially listed as TC-36P for historical purposes. (Thanks to Maj Roger Edson, USAF, of JTWC for this tidbit of information.) Tropical Cyclone Bart (TC-37P) 28 April-3 May ----------------------------------------------- Tropical Cyclone Bart developed farther east than any previous cyclone in this long and active South Pacific season, although it did not move as far east or south as did Ursula back in February. The Tropical Disturbance Summary issued by Nadi at 0600 UTC on 26 Apr mentioned a tropical disturbance at 17S, 137W. Another Summary at 1800 UTC on 28 Apr mentioned one near 15S, 144W. This was the system which developed into Bart. It is not clear to the author if this was a new disturbance or if the earlier disturbance had migrated several hundred miles westward. The developing cyclone was part of a very large area of lower-than-normal pressure which contained the remnants of Alan. The first depression bulletin (at 2200 UTC on 28 Apr) placed the center about 350 nm east-northeast of Tahiti. This position is in the midst of the Tuamotu Islands. Around 1200 UTC on the 29th stations in the vicinity were reporting 2 to 3 mb pressure falls with strong winds. Hau (WMO 91944) reported east winds of 25 kts at 29/1200 UTC. By 1800 UTC Hau was reporting southeast winds of 35 kts with the pressure having fallen 5 mb more. Tropical Cyclone Bart was named at this time and was centered about 575 nm east of Tahiti near the island of Hau. Bart initially began moving at a fairly good clip to the south and south-southeast, but a blocking ridge strengthened on the 30th to the south and caused the cyclone's motion to slow down. Bart's winds peaked at 45 kts on 30 Apr and began to weaken steadily on 1 May. Satellite imagery around 01/0000 UTC showed that the main convective area had been sheared about 60 nm to the southeast of the exposed low-level center. The system was downgraded to a depression at 0600 UTC on the 1st but some gales were still forecast to occur in the southern semi-circle. After 01/1200 UTC Bart began to accelerate again in more of an east- southeasterly direction. The last bulletin found the weakening system about 50 nm north of Pitcairn Island around 0000 UTC on 3 May. The author has received one report of up to 10 fatalities caused by Tropical Cyclone Bart, but it is unclear exactly on which island(s) these occurred. Hopefully, more information will be forthcoming, and if so, it will be reported in the summary for May. *********************************************************************** 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 April as an example: apr98.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 April summary is the seventh 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 website (courtesy of Michael Bath): 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 *********************************************************************** *********************************************************************** +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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.