Movatterモバイル変換

MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY MAY, 2004 (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.) ************************************************************************* MAY HIGHLIGHTS --> Flooding from Caribbean LOW causes much loss of life on Hispaniola --> Year's second super typhoon strikes Philippines --> Tropical storms form in Northeast Pacific and North Indian Ocean --> Bay of Bengal hurricane delivers damaging strike to Myanmar ************************************************************************* ***** Feature of the Month for May ***** SURVEY RESULTS - SUBTROPICAL CYCLONE QUESTIONS During the summer (boreal) of 2003, I sent another one of my famous surveys to the members of an informal tropical cyclone discussion group of which I am a member. I also recently sent it to a few other persons in the tropical cyclone community. I intend to present the results of the survey as monthly features spread over several months, beginning with the May, 2004, summary. The survey consisted of ten multiple-choice questions dealing with various tropical or subtropical cyclone-related issues, and two or three questions will be considered each month. The persons responding to the survey are listed below. A special thanks to each for taking the time to respond to the questions. Michael Bath - New South Wales, Australia Bruno Benjamin - Guadeloupe, French West Indies Eric Blake - TPC/NHC, Miami, Florida, USA Pete Bowyer - Canadian Hurricane Centre, Halifax, Nova Scotia, Canada Kevin Boyle - Newchapel Observatory, Stoke-on-Trent, UK Jeff Callaghan - BoM, Brisbane, Queensland, Australia Simon Clarke - Brisbane, Queensland, Australia Tony Cristaldi - NWS Office, Melbourne, Florida, USA Roger Edson - University of Guam, USA Chris Fogarty - Canadian Hurricane Centre, Halifax, Nova Scotia, Canada James Franklin - TPC/NHC, Miami, Florida, USA Bruce Harper - Brisbane, Queensland, Australia Julian Heming - UK Meteorological Office, UK Rich Henning - Eglin AFB, Florida, USA/Also 53rd Weather Recon. Squadron Karl Hoarau - Cergy-Pontoise University, Paris, France Greg Holland - BoM, Australia Mark Kersemakers - BoM, Darwin, Northern Territory, Australia Mark Lander - University of Guam, USA Chris Landsea - AOML/HRD, Miami, Florida, USA Gary Padgett - Alabama, USA Michael Pitt - US Navy David Roberts - TPC/NHC, Miami, Florida, USA David Roth - NOAA/HPC, Maryland, USA Matthew Saxby - Queanbeyan, New South Wales, Australia Carl Smith - Queensland, Australia Phil Smith - Hong Kong, China John Wallace - San Antonio, Texas, USA Ray Zehr - Colorado State University, Ft. Collins, Colorado, USA For each of the survey questions, the format will be as follows: (1) the question as it appeared in the original survey (2) summary of the responses to each of the possible choices (3) some of the comments from various respondents Following this I will attempt to present an analysis of the issues plus interject my opinions on the subject. The monthly feature for May will focus on the first three questions, all of which were related to the somewhat problematic topic of hybrid and/or subtropical cyclones. These systems present classification problems both to the real-time forecaster and to those involved in climatological studies of tropical cyclones since the Best Track data sets among the various warning agencies differ in their handling of these systems. Some of the problems include: (1) should there be two or three operational classes of marine cyclones, (2) should subtropical/hybrid systems be named in the manner of tropical cyclones, and (3) exactly what features should characterize those systems classified as subtropical cyclones. There were 28 persons who responded to the survey questions. For some questions, certain persons did not specify an answer, so the total number of votes might not always add up to 28. Also, in some cases the respondent was undecided between two of the choices. In those cases I assigned 1/2 vote to each of the two choices. A word about the comments included below: this article is extremely long as it is, and I could not possibly include all the comments which the various respondents made. I have selected certain ones which seem to cover the various issues well, as well as a few which cast a different slant on the questions. Question #1 - Number of Cyclone Classes --------------------------------------- (1) The question was: For operational warning strategies for marine cyclones, should there be 2 or 3 categories? (A) Two classes--tropical and extratropical (or non-tropical) (B) Three classes--tropical, subtropical (or hybrid), extratropical (non-tropical) (2) Summary of Responses (A) Two classes: 6.5 votes - 23% (B) Three classes: 21.5 votes - 77% (3) Some Comments Chris Landsea: (A) "I think that 2 classes probably would be best to reduce the confusion. One could lump subtropicals in with tropical cyclone warnings, and then in the Best Track indicate their correct classification." Dave Roberts: (B) "I would've loved to change the policy on ST systems at JTWC. Unfortunately, I was a minority. Tropical and ST should be treated similarly (i.e., NHC's Op-Plan)." Julian Heming: (B) "I think it is worth having a separate ST category since the wind structure and distribution of convection are usually different from complete tropical systems. However, education on the definitions is needed, so that the danger of ST systems is not underestimated." Mark Lander: (B) "I think the ST classification serves some purpose, if only to give the warning agencies an avenue to provide timely advisories, rather than waiting before it is too late (i.e., an eye forms and there is an instant hurricane)." Matthew Saxby: (B) "While aware that cyclones are a spectrum rather than nice neat groupings, I think the current BASIC classification is OK and should be left alone, though perhaps definitions need to be standardised globally and tightened up." Michael Bath: (A) "Three might be OK for the enthusiasts, but would confuse the public." Tony Cristaldi: (B) "Assuming this includes the OPC operations. Note that NON-ST (frontal) hybrids such as the western Atlantic cyclone of 5-7 July 2002 could still be handled by OPC as extra- tropical systems if so desired. The line becomes blurred in cases such as these when it comes to the whole frontal/non-frontal debate, but fortunately I've observed these types of systems to be relatively rare, or relatively short-lived and transitional when in that particular state, even moreso than true subtropical cyclones." Rich Henning: (B) "Some systems ARE hybrids, with a cold core aloft, being fed by PVA (positive vorticity advection), deriving much of their energy through baroclinicity, but with deep convection close to a LLCC and a contracting windfield with max winds drawing closer to the center. Some eventually replace the cold core aloft with a warm core and isolate themselves from the baroclinic forcing (by getting out of phase with the upper-level trough supporting it and being "left behind", so to speak). When they reach the point that they are drawing more energy from the sea surface through inner core convective processes than from baroclinic forces, reclassifying them as tropical storms should be considered. I think subtropical warnings to the public are OK--I am not enthusiastic about it--but the benefits derived by maintaining a more consistent and compre- hensive historical climatology outweigh the small amount of confusion it may generate in the public. The only other answer would be to maintain a separate Best Track climatology (which includes STs) different from the public warnings of only tropical and non-tropical. However, that might present a host of problems with insurance companies and other "Monday morning quarterbacks" second guessing NHC and thinking information was being "withheld from the public" (ala the Claudette controversy)." Question #2 - To Name or Not To Name ------------------------------------ (1) The question was: What is your opinion regarding naming of subtropical cyclones? (A) Should be named from regular TC name list (e.g., NHC, La Reunion) (B) Should be named but from alternate name list (e.g., Greek alphabet, phonetic alphabet, etc) (C) Should not be named (2) Summary of Responses (A) Named from regular TC list: 20 votes - 74% (B) Named from alternate list: 3 votes - 11% (C) Should not be named: 4 votes - 15% (3) Some Comments David Roth (A): "Because that is how it was generally done (purposely or not) before 1972, so it actually is more consistent with past operational practice." Julian Heming (A): "This is a difficult one. Since the majority of recent Atlantic STs have become tropical, it makes sense to have one name list for both, although I can understand those who might prefer not to name them at all, but keep names for just tropical systems." Kevin Boyle (C): "Should not be named because the public are going to be confused and NOT take as much notice of a named subtropical LOW. Names should only be reserved for fully tropical systems, i.e., tropical storms and hurricanes." Mark Lander (A): "In order to avoid confusion at that magical point when the cyclone is advanced from ST to TC, the system should have a name that does not change. I like the Greek letter naming system for unnamed TCs that are found in post-analysis (as you have done for some of the western Pacific unnamed TCs)." Tony Cristaldi (A): "Much simpler philosophy, since there is a cyclone "spectrum" of tropicality, subtropicality, and extra- tropicality and cyclones often find themselves within more than one part of this spectrum." Simon Clarke (A): "For all intents and purposes some of these systems have the same impacts as cyclones. But most particularly where there is a chance of a real impact on land, lives, etc. The recent S QLD hybrid I believe should have been named. BoM even went so far as using the cyclone siren for this storm, which I don't think they have ever done previously." Ray Zehr (C): "I prefer the previous way of naming only if they transition to tropical, although I don't see the change as a big problem as long as "tropical only" are counted in seasonal statistics." Question #3 - Just What Is a Subtropical Storm ---------------------------------------------- (1) The question was: Should the definition of a subtropical storm include all intermediate cases between a classic frontal extra- tropical cyclone and a well-developed deep warm-core tropical cyclone? (A) Yes (B) No (2) Summary of Responses (A) Yes: 15 votes - 60% (B) No: 10 votes - 40% (3) Some Comments Chris Fogarty: (A) "Fronts should be shed, however! We would be naming subtropical cyclones out of deep winter storm centers if we didn't specify in the definition that fronts need to be shed or well-removed from the subtropical warm core. It is a grey area between a well-formed subtropical system and a purely tropical one. Kind of the same uncertainty between defining the other way--from tropical to extratropical." Chris Landsea: (A) "Yes, as long as it is non-frontal." Dave Roberts: (B) "No--should be defined as a non-frontal LOW, although a meso-LOW in a weakening horizontal shear zone should also be acceptable. Origin and core characteristics as well as convection/cloud structure should also be taken into consideration." David Roth: (A) "Yes, but it can NOT include cyclones along existing surface cold/stationary fronts. Until someone revises the Hebert/Poteat paper or TPC changes its definition, there is no other standard." Eric Blake: (B) "No, convection is pretty necessary." James Franklin: (B) "No, TCs and STs are (should be) completely non-frontal." Tony Cristaldi: (B) "As mentioned above, I have found that true non-ST hybrids, those storms which exhibit central warm-core features with both horizontal and vertical continuity, are relatively rare and of a transitory nature. If you were to bring in frontal hybrids into the mix, I fear that you would be bringing in a type of cyclone whose wind field could sometimes be so expansive as to bring in some ridiculous wind radii into the analysis/forecast. As such, I would favor this type of cyclone being handled by OPC and treated as more of an extratropical entity." Ray Zehr: (B) "I think 'extratropical transition' can be distinguished from a 'subtropical storm'." Analysis and Gary's Opinion --------------------------- As I see things, the primary problem with classification of subtropical cyclones has been twofold: (1) lack of a detailed definition which touches on all the various types of intermediate systems, and (2) the general acceptance of three classes of cyclones but trying to fit them into two classes operationally--and often in post-analysis. And along with this, inconsistent handling of these systems over the past one-third century since they were first identified publicly as subtropical cyclones (at least in the Atlantic basin). The bottom line for me is: what approach will help to promote a consistent TROPICAL cyclone climatological database. As far as the official Best Track file is concerned, I am as concerned about a brief minimal tropical cyclone as I am about a Gilbert or a Camille or a Tip or a Geralda or a Zoe. I want to see the "signal noise" reduced as much as possible. For the Northwest Pacific basin, the inclusion or exclusion of one system is fairly insignificant, but for the Atlantic one cyclone represents 10% of the annual average. And for the North Indian Ocean region, one storm constitutes about 20% of the annual average. Hence, for the lower-frequency tropical cyclone basins, the "signal noise" should be reduced as much as possible. Having a firm decision about how to treat subtropical cyclones with regard to the historical tropical cyclone databases will help very much toward achieving this goal, especially in STC-rich areas such as the North Atlantic, Southwest Indian Ocean, and Queensland region. On the survey I voted for Option B (3 classes), but I could be content with having 2 classes IF the warning centers in general would decide to classify as TROPICAL cyclones ALL non-frontal LOWs that had a significant amount of organized convection reasonably close to the central region of the storm. (Just what is "significant" and "reasonably close" would of course have some inherent subjectivity, but an attempt could be made to quantify the terms somewhat.) Given that 3/4 of the respondents to the survey voted for three classes, perhaps that is the way to go. I reject the oft-stated idea that the public would be hopelessly confused with three categories of cyclones. Most members of the general public I know, and very likely the majority of those I don't know, have learned quite well how to utilize personal computers (PC) proficiently in their daily activities. I hardly think learning the concept of three classes of marine cyclones begins to approach the difficulty of learning how to use a PC! The third question was perhaps not stated the best--some respondents voted for opposite choices but, based on their comments, basically agree on the issue. I think part of the problem again lies with a definition: exactly what does frontal mean. To some persons a front must involve a fairly strong baroclinic zone with a well-defined cloud band evident in satellite pictures. But to others a weak temperature gradient qualifies as a front. As I understand things, when NHC began operationally using the ST category under Dr. Simpson's direction in 1972, the plan was to follow a course akin to Option A. But the observation of such systems as warm-core hybrids with central convection, extratropical "bombs", polar LOWs, Mediterranean cyclones, Australian East Coast LOWs, etc over the years has really blurred the picture. For a period of about 15 years, NHC did not utilize the subtropical cyclone category at all with one exception--the April, 1992, subtropical storm. Now that NHC has resurrected the category operationally, they seem to be very conservative regarding issuing warnings on subtropical storms, and require that the system be completely non-frontal and usually well on its way to becoming a tropical storm. Since 2000, all the systems identified operationally as subtropical depressions or storms have eventually become named tropical cyclones: pre-Leslie (2000), pre-Karen and pre-Olga (2001), Gustav and Kyle (2002), and Ana (2003). This leads to the second question: the issue of naming subtropical cyclones. I voted for Option A (name from the regular TC list), but this is a weak opinion. I am just as comfortable with them not being named, but given that I feel very strongly that a named system gets the attention of the public much more than an unnamed one, the current operational practice of NHC and the Southwest Indian Ocean warnings agencies is probably the best procedure. As Mark Lander has stated, having the first tropical cyclone advisory refer to a storm near or exceeding hurricane intensity is not in the best interest in reducing confusion and, more importantly, in saving lives. ************************************************************************* ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for May: Possible subtropical LOW Atlantic Tropical Activity for May ---------------------------------- The month of May lies outside the official June to November Atlantic hurricane season, and tropical storms and hurricanes are quite rare during the month. Since 1886, only three May hurricanes have been noted, whereas May tropical storms usually appear about every 8 to 10 years on the average. However, it has now been 23 years since a named storm formed during the month, the last being Tropical Storm Arlene in 1981. There was a system in May, 2004, which formed in the Caribbean Sea and tracked slowly northeastward, bringing very large rainfall totals to the island of Hispaniola, leading to disastrous flooding. A short report on this system follows. Caribbean Sea Low-pressure System --------------------------------- A broad area of low pressure formed over Nicaragua and Costa Rica around 19 May and produced heavy rains over portions of Central America. NHC issued a Special Tropical Disturbance Statement (STDS) that morning in order to raise an alert about the potential for life-threatening rains. The system drifted slowly eastward into the open Caribbean Sea, and another STDS was issued on the morning of the 23rd with the focus now being the threat of heavy rains in Jamaica, eastern Cuba, Puerto Rico and Hispaniola. The combination of the Caribbean LOW and high pressure over the southwestern Atlantic was forecast to produce winds of 20-25 kts over the Greater Antilles and adjacent waters. According to David Roth, a meteorologist at the Hydrometeorological Prediction Center in Maryland, the system was a closed surface LOW with an expansive wind field, was non-frontal, and had convection northeast of the center. In addition, there was a large, linear inflow band near the Lesser Antilles well east of the center. In David's opinion, the system exhibited some characteristics of a subtropical system. He also remarked that in some ways it resembled Tropical Storm Frances in 1998 in the Gulf of Mexico. Frances was clearly a warm-core system with a huge wind field and a long inflow band. To the author's knowledge, no gales were reported in association with the May Caribbean system. As the LOW moved slowly across the Greater Antilles and into the open Atlantic, very heavy rains fell across the region, especially in Haiti and the Dominican Republic. Following are a few representative rainfall amounts sent by Huang Chunliang and David Roth: Country Station WMO ID Lat Lon Alt (m) Rainfall (mm) ------------------------------------------------------------------------ Dom. Rep. Caucedo 78485 18.4 N 69.7 W 18 210.2 Dom. Rep. Santo Dom. 78486 18.4 N 69.9 W 14 189.1 Dom. Rep. Barahona 78482 18.2 N 71.1 W 26 150.3 Barbados Catbalogan 78954 13.0 N 59.5 W 56 107.9 The above amounts were recorded during the 24-hour period from 23/1200 to 24/1200 UTC. (Thanks to Chunliang and David for sending them.) The death toll from mudslides and flooding in the Dominican Republic and Haiti has been placed at around 2000. This represents the greatest natural disaster on the island of Hispaniola since Hurricane Flora in 1963 claimed well over 5000 lives. Over 1000 bodies were discovered in Mapou, a remote town near the Haitian/Dominican border that was all but destroyed. Another 500 persons were killed elsewhere in southeastern Haiti and 158 in the riverside town of Font Verettes. Over 300 bodies were recovered in the Dominican Republic with hundreds more missing. Thanks to John Wallace for sending the press report from which the above paragraph was taken. The full report can be found at: http://www.guardian.co.uk/international/story/0,3604,1225768,00.html> Also, additional stories on the severe flooding in the Caribbean region and in Central American can be found at the following URL: http://www.reliefweb.int/w/rwb.nsf/vLND> (Report written by Gary Padgett) ************************************************************************* NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for May: 1 tropical storm Sources of Information ---------------------- Most of the information presented below was obtained from the various tropical cyclone products issued by the Tropical Prediction Center/National Hurricane Center (TPC/NHC) in Miami, Florida (or the Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii, for locations west of longitude 140W): discussions, public advisories, forecast/advisories, tropical weather outlooks, special tropical disturbance statements, etc. Some additional information may have been gleaned from the monthly summaries prepared by the hurricane specialists and available on TPC/NHC's website. All references to sustained winds imply a 1-minute averaging period unless otherwise noted. Northeast Pacific Tropical Activity for May ------------------------------------------- A tropical storm develops in the Eastern North Pacific about once every other year, while a hurricane forms about every fourth year. During the period 1992-1999 inclusive, only one May tropical storm developed. However, starting with 2000, May cyclones began forming each year, and 2004 was no exception. Tropical Storm Agatha developed on 22 May and moved northwestward to near Socorro Island, where it stalled and weakened. A brief report on this cyclone follows. TROPICAL STORM AGATHA (TC-01E) 22 - 25 May ----------------------------------------- The official TPC/NHC storm report on Agatha, written by Lixion Avila, is already available online at the following link: http://www.nhc.noaa.gov/2004agatha.shtml?> Since the report is already online, I'll be brief in my comments about Agatha. A weak tropical wave crossed Central America and interacted with a monsoonal trough in the Eastern North Pacific. The system was upgraded to Tropical Depression 01E at 22/0000 UTC when located about 500 nm south-southeast of Cabo San Lucas, and then upgraded to Tropical Storm Agatha twelve hours later. The estimated peak intensity of 50 kts occurred at 23/0000 UTC. Agatha was in the vicinity of Socorro Island at this time, and the storm became quasi-stationary as it rather quickly weakened during the next couple of days. No damage or casualties are known to have resulted from Tropical Storm Agatha. The peak intensity of Agatha is fraught with uncertainty. SSM/I and TRMM imagery from around 22/1400 to 23/0230 UTC revealed a ring of precipitation that resembled an eyewall. Lixion's report points out that Agatha's peak intensity was probably higher than Dvorak estimates, and laments the fact that no established technique exists to estimate tropical cyclone intensity from such microwave features. In his opinion the 50-kt peak intensity in this case was particularly uncertain. In some e-mail discussion, Karl Hoarau and Mark Lander argued to make the case that Agatha was a hurricane. Karl indicated that he'd looked at all Atlantic cyclones from 1997-2003 with an intensity in the 45-70 kt range and for which reconnaissance data was available. He states that in every case where the storm had winds estimated in the 45-55 kt range, the 85-GHz signature was weaker than Agatha's signature. It seems that one thing which perhaps was a strong factor in keeping Agatha's real- time intensity held at 45 kts was the fact that the three satellite fix agencies rendered T-numbers of only 3.0. However, Dave Roberts wrote that he was getting a 4.0 based on the MET and PT, and if one went with a visible banding eye in the visible, it could be 3.5 to 4.0 with a banding feature addition. Chris Velden also stated that the AODT got a CI number of 3.8 with a maximum Data-T of 4.2. So it appears that the case can be made from Dvorak analysis alone for Agatha to have peaked near hurricane intensity. (Report written by Gary Padgett) ************************************************************************* NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for May: 1 tropical storm ** 1 typhoon ++ 1 super typhoon ** - classified as a tropical storm by JTWC only ++ - classified as a typhoon by JTWC only Sources of Information ---------------------- Most of the information presented below is based upon tropical cyclone warnings and significant tropical weather outlooks issued by the Joint Typhoon Warning Center of the U. S. Air Force and Navy (JTWC), located at Pearl Harbor, Hawaii. In the companion tropical cyclone tracks file, I normally annotate track coordinates from some of the various Asian warning centers when their center positions differ from JTWC's by usually 40-50 nm or more. All references to sustained winds imply a 1-minute averaging period unless otherwise noted. Michael V. Padua of Naga City in the Philippines, owner of the Typhoon 2000 website, normally sends me cyclone tracks based upon warnings issued by the Japanese Meteorological Agency (JMA) and the Philippines' Atmospheric, Geophysical & Astronomical Services Administration (PAGASA). Also, Huang Chunliang of Fuzhou City, China, sends data taken from synoptic observations around the Northwest Pacific basin. A very special thanks to Michael and Chunliang for the assistance they so reliably provide. In the title line for each storm I have referenced 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 warning responsibility. Northwest Pacific Tropical Activity for May ------------------------------------------- The month of May was fairly active in the Northwest Pacific basin with three significant tropical cyclones forming. The unusual thing was that they all formed practically simultaneously around mid-month, leading to a triple-storm situation in the Western Pacific. The first of the three, Super Typhoon Nida/Dindo, was the strongest, skirting the eastern coast of Luzon and passing directly over Catanduanes Island. Tropical Cyclone 05W was a weak system which meandered just off the southern Vietnamese coast for several days, being upgraded to a minimal tropical storm by JTWC only for a period of 12 hours. Typhoon Omais was a midget cyclone which threatened to bring more misery to typhoon-ravaged Yap, but remained just to the south of the island, and with the storm being so tiny, Yap remained just on the fringes of the gale radius. Reports on all three of the systems, authored by Kevin Boyle, follow. SUPER TYPHOON NIDA (TC-04W / TY 0402 / DINDO) 13 - 22 May ---------------------------------------------- Nida: contributed by Thailand, is a Thai feminine name A. Introduction --------------- Super Typhoon Nida occurred in conjunction with two other tropical cyclones, Tropical Storm 05W and Typhoon Omais, and was by far the strongest of the three. This multiple storm outbreak, the first of the year, required JTWC to issue warnings on three storms simultaneously in the Western North Pacific. Nida, the second super typhoon of 2004, paralleled the coast of the eastern Philippines, causing extensive damage, flooding and loss of life. B. Storm Origins ---------------- On 12 May an area of convection persisted within an active monsoon trough approximately 220 nm southwest of Palau. QuikScat, microwave and multi-spectral imagery all showed a weak LLCC near the suspect area. An upper-level analysis showed a favourable environment for tropical cyclone formation with good diffluence aloft and weak vertical wind shear. The suspect area was judged to have a poor potential for development by JTWC at 0000 UTC, 12 May, but this was upgraded to fair at 13/0600 UTC as the system's broad LLCC consolidated under the cycling deep convection. Development continued and a TCFA was issued at 13/1200 UTC, and was followed at 1500 UTC by the first warning on Tropical Depression 04W. C. Synoptic History ------------------- At 13/1200 UTC Tropical Depression 04W formed 190 nm east of Palau, and at the time was moving slowly westward at 3 kts. The MSW was 25 kts near the centre as indicated by a QuikScat pass. This, combined with enhanced infrared satellite time-lapse imagery, showed further organization of the deep convection over the LLCC. Rapid intensification was a characteristic feature of this storm. It only took five warnings (or 30 hours) for this system to attain minimal typhoon status. TD-04W became a 50-kt tropical storm at 0000 UTC, 14 May, while located 175 nm west-southwest of Palau (the centre had been relocated six hours earlier.) JMA assigned the international name Nida as soon as they raised the 10-min average winds to 40 kts at 14/0600 UTC. (PAGASA had already dubbed the cyclone Dindo by this time.) Turning northwestward, Nida became a 65-kt typhoon at 14/1200 UTC with 37 GHz microwave imagery revealing a developing eye; however, this feature was still not evident in enhanced infrared satellite imagery. At 15/0000 UTC Typhoon Nida was tracking west-northwestward at 6 kts some 600 nm east-southeast of Manila, Philippines. After a brief hiatus, further strengthening occurred and at 15/1800 UTC the MSW had reached major typhoon intensity, i.e. 100 kts. Equatorward outflow was excellent and Nida was receiving a boost from an upper-level LOW situated to the northeast. A mid-level ridge to the north was guiding the typhoon north- westward and was expected to continue to do so for the next 48 hours. Thereafter, a longwave trough was forecast to weaken the ridge and shift the track poleward. Continuing on its northwestward journey, Typhoon Nida reached a position 420 nm southeast of Manila at 0000 UTC on 16 May with a MSW of 115 kts. Six hours later, Nida was upgraded to a super typhoon and ultimately reached a peak intensity of 140 kts at 16/1200 UTC. At its strongest, Nida's outer 35-kt winds extended no more than 150 nm on the eastern side. The wind profile on the western side was smaller with gales extending no more than 110 nm from the centre. The radii of 50-kt and 100-kt winds around the center were estimated at 60 nm and 25 nm, respectively, making Nida an average-sized typhoon. Microwave imagery at 16/1102 UTC showed a well-defined 25-nm eye with banding features. The MSW fell back to 130 kts as the eye passed over Catanduanes Island, Philippines, around 17/0000 UTC. After passing over Catanduanes Nida began to turn more to the north. This was confirmed after the typhoon had made a small stair-step wobble at 17/0600 UTC, the eye being located approximately 180 nm east-northeast of Manila. Super Typhoon Nida had undergone a modest re-intensification phase, resulting in an increase in the MSW to 135 kts. Slow weakening began at 17/1800 UTC as Nida pushed north through the ridge axis. At 0000 UTC on 18 May Super Typhoon Nida was moving northward at a slower pace some 610 nm south-southwest of Kadena AB, Okinawa. The MSW was still at super typhoon strength and 130 kt-winds were maintained for another six hours. The storm still looked impressive with a well- defined, symmetrical eye and sustained deep convection as seen on multi- spectral imagery. Diffluence was excellent, aided by a migratory trough to the west. Weakening began in earnest at 18/1200 UTC and Nida was downgraded from super typhoon intensity. Animated infrared satellite imagery revealed a cloud-filled eye and a decrease in deep convection. The western portion of the eyewall was degraded as recurvature was completed at 1800 UTC with Nida turning toward the northeast. Typhoon Nida was accelerating northeastward at 19/0000 UTC with winds falling below 100 kts by 1200 UTC. The storm at that time was located approximately 220 nm south-southwest of Okinawa. Six hours later, the system began to interact with the baroclinic system over Japan, the overall appearance becoming elongated as a result. Turning east- northeastward, Nida had accelerated to around 20 kts while further weakening to 80 kts by 20/0000 UTC. This intensity was maintained through the 20th while the forward speed increased to roughly 30 kts. Nida was downgraded to a tropical storm at 1800 UTC while located 290 nm south of Tokyo, Japan, and sprinting at nearly 40 kts. Extratropical transition was complete by 21/0600 UTC and JTWC ended warning coverage at this time. The MSW was estimated at 45 kts on this final warning which placed the center approximately 300 nm east-southeast of Misawa, Japan. JMA continued to track the extratropical storm through 22/1200 UTC as it slowly weakened over waters well to the east of northern Japan. The estimated minimum CP by JMA during Nida's lifetime was 935 hPa. JMA, PAGASA and the CWB of Taiwan estimated Nida's peak 10-min avg MSW at 90 kts, whereas NMCC and HKO estimated the peak winds at 110 kts. A sustained 10-min avg wind of 101 kts was recorded at Virac in the Philippines as the typhoon crossed Catanduanes Island. (See the following section.) D. Meteorological Observations ------------------------------ The following are rainfall reports, forwarded by both Huang Chunliang and Michael Padua. Many thanks to both these gentlemen for their help. Station WMO Rainfall Period Name Code Coordinates Alt(m) (mm) (Times=UTC) ---------------------------------------------------------------------- Catarman 98546 12.5 N 124.6 E 7 231.5 16/0000-17/0000 Virac 98446 13.6 N 124.2 E 40 224.0 16/0000-17/0000 Masbate 98543 12.4 N 123.6 E 6 196.8 16/0000-17/0000 Catbalugan 98548 11.8 N 124.9 E 5 141.1 16/0000-17/0000 Borongan 98553 11.6 N 125.4 E 3 117.9 16/0000-17/0000 Legaspi 98444 13.1 N 123.7 E 17 116.3 16/0000-17/0000 Masbate 98446 12.4 N 123.6 E 6 167.4 17/0000-18/0000 San Jose 98531 12.4 N 121.0 E 3 155.8 17/0000-18/0000 Legaspi 98444 13.1 N 123.7 E 17 107.2 17/0000-18/0000 Dagupan 98325 16.1 N 120.3 E 2 104.6 17/0000-18/0000 Iba 98324 15.3 N 120.0 E 5 104.2 19/0000-20/0000 The following are 41-hour accumulated rainfall totals recorded in Camarines Sur: Camaligan/Naga City - 150 mm Ombao - 270 mm Bato - 209 mm Buhi - 152 mm Minamidaitojima (WMO 47945, 25.83N/131.23E, Alt 15 m) recorded a wind gust of 62 kts at 19/2203 UTC. The station's minimum SLP of 972.9 hPa was measured at 20/0016 UTC. The maximum 10-min avg wind of 38 kts was recorded at 20/0010 UTC, and the peak gust, measured around the same time, was 67 kts. The storm total rainfall, recorded between 19/1500 and 20/1500 UTC, was 71.0 mm, and a peak hourly rainfall of 32.0 mm was measured between 2249 and 2349 UTC on the 19th. The Virac weather station on Catanduanes Island (WMO 98446) recorded the following SLP readings and 10-min avg winds at the indicated hours on 17 May: Time (UTC) SLP (hPa) 10-min Avg Winds (kts) Direction ------------------------------------------------------------------ 17/1900 970.5 79 N 17/2000 969.6 87 NNW 17/2100 967.0 87 WNW 17/2200 965.8 101 W Note: The elevation of the Virac weather station is 39 metres. E. Damage and Casualties ------------------------ Media reports indicate that twenty people were killed and up to eight injured in typhoon-induced incidents. Ten persons are still reported missing at the time of this writing. Five lives were lost when the M/B St. Martin (a motorized banca) foundered in heavy seas just 2 km off Pilar port, Camotes Island. Four additional persons are still unaccounted for. Evacuation centers were opened to accommodate up to 634 families (2,986 persons) while ferry cancellations left 15,057 passengers stranded. At the time of this writing, the total damage to infrastructure, agriculture, and property is estimated at 263 million pesos (latest figure by OCDR-5). A total of 5,938 homes were damaged and 4,071 completely destroyed. A tornado caused P3,670,000 worth of damage in Guimba, Nueva Ecija. One official estimated damage to agriculture at P33 million. (Report written by Kevin Boyle) TROPICAL STORM (TC-05W) 14 - 20 May ---------------------------------- Tropical Storm 05W originated from a small disturbance that formed east of Vietnam and was first mentioned in JTWC's STWO at 1500 UTC on 13 May when it was located 285 nm east-southeast of Ho Chi Minh City, Vietnam. A weak LLCC under cycling deep convection was depicted in microwave and enhanced infrared satellite imagery. The development potential was assessed as poor initially, but was later upgraded to fair, and this was immediately followed by a TCFA at 14/0600 UTC as the suspect area continued to develop under a favourable upper-level environment. The potential for development remained good and the first warning was issued at 15/1200 UTC. At the time of the first warning Tropical Depression 05W was located approximately 220 nm east-southeast of Ho Chi Minh City, Vietnam, and moving west-southwestward at 7 kts. Infrared satellite imagery revealed a partially-exposed LLCC to the east of the deep convection. This became fully-exposed as the system briefly turned northward at 0000 UTC on 16 May before curving toward the west-northwest six hours later, bringing it to within 125 nm of Ho Chi Minh City to the east-southeast. At this time, TD-05W was upgraded to a tropical storm with the MSW reaching 35 kts. This turned out to be the peak intensity. The system didn't look that much more impressive as a tropical storm, and JTWC soon downgraded it back to tropical depression status at 16/1800 UTC. After staggering a little closer to the coast of Vietnam, Tropical Depression 05W turned abruptly towards the northeast and accelerated to around 11 kts. Multi-spectral imagery depicted a fully-exposed LLCC east of the convection similar to the day before. Finally, the convection and the LLCC split and went their separate ways, and based on this, JTWC issued the final warning at 17/0600 UTC. On 18 May the remnants of Tropical Depression 05W perked up with convection returning and persisting in association with a well-defined LLCC. This prompted JTWC to upgrade the development potential to good once more. This was lowered to poor again at 0600 UTC on 19 May after the convection had decreased and become cyclic in nature. The weak LLCC was located 230 nm west-southwest of Manila on the next STWO at 20/0600 UTC, and even though convection organized for a second time, this was the last mention of this system. During the post-warning (per JTWC) stage of TD-05W, JMA continued to carry the LOW as a weak tropical depression in their High Seas bulletins through 1800 UTC on 20 May. (JTWC was the only agency which treated this system as a tropical storm.) There were no known damage or casualties associated with Tropical Storm 05W. (Report written by Kevin Boyle) TYPHOON OMAIS (TC-06W / STS 0403 / ENTENG) 16 - 23 May ------------------------------------------------ Omais: contributed by the United States, is the Palauan word for 'wandering around' A. Introduction --------------- Typhoon Omais was the third of three significant tropical cyclones during May and occurred during a triple-storm outbreak together with Super Typhoon Nida and Tropical Storm 05W. This midget typhoon passed only a whisker's breadth away from Yap Island before recurving north and northeast and dissipating. B. Storm Origins ---------------- At 0600 UTC 14 May a new area of convection was noted approximately 250 nm southwest of Chuuk. JTWC included this new suspect area in their STWO at 0600 UTC, 14 May, and assessed it as having a poor potential for development. Animated multi-spectral satellite imagery revealed a possible weak LLCC with loose, cycling convection. An upper- level analysis indicated a moderate environment with weak to moderate wind shear and good diffluence aloft. The potential was raised to fair at 15/0000 UTC after significant improvement in organization of the deep convection over a definitive LLCC had been observed. After a TCFA was issued at 15/2200 UTC, the initial warning on Tropical Depression 06W followed. C. Synoptic History ------------------- At the time of the first warning Tropical Depression 06W was moving west at 14 kts, being located some 525 nm east of Palau. Continuing west, it was upgraded to tropical storm status at 16/1200 UTC. The MSW increased a little more to 40 kts and this intensity was maintained through much of the 17th. At 17/0600 UTC animated multi-spectral satellite imagery showed the system with a disorganized, partially- exposed LLCC with the deep convection blowing off to the west. The storm had turned to a northwesterly path, and this heading took it to within 140 nm of Yap at 17/1200 UTC. At this time, enhanced infrared satellite animations showed organizing deep convection over the LLCC, and Tropical Storm Omais began to rapidly intensify with the MSW upped to 60 kts at 1800 UTC. (Editor's Note: The system did not officially become Tropical Storm Omais until 0000 UTC on 18 May, when JMA upgraded it to a 35-kt tropical storm--considerably less than JTWC's estimated MSW of 60 kts.) Having suffered badly from the passage of Typhoon Sudal only a month earlier, things were looking rather bleak for the island of Yap at 18/0000 UTC. The continued northwesterly heading brought the center to approximately 50 nm south-southeast of Yap. (At 18/0300 UTC Warning #9 was amended to mention that Omais had been relocated to a position about 60 nm directly south of Yap to tie in with fixes from microwave and multi-spectral imagery.) The public advisory at 18/0059 UTC said it all: "Damaging winds are imminent at Yap and neighbouring islands. Tropical Storm 06W is forecast to pass over or very close to Yap as a Category 1 typhoon this evening. Residents of Yap should complete preparations for destructive winds as soon as possible." However, Lady Luck was smiling down on Yap. At 0600 UTC Omais turned west-northwestward and accelerated to 11 kts, sparing the island a direct hit. Also, the fact that Omais was a midget tropical cyclone seems to have worked to Yap's advantage. The radius of gale-force winds was no more than 50 nm in the northern quadrants and 70 nm to the south. More importantly, the radius of destructive 50-kt winds was only 20 nm to the north, so likely Yap only received winds gusting to barely gale force as Omais passed by to the south. Continuing west-northwestward, Omais was upgraded to minimal typhoon status at 1800 UTC on 18 May, and the MSW of 65 kts was to be the peak intensity per JTWC's warnings. This intensity was maintained through the 19th. Microwave imagery at 1200 UTC revealed a possible banding eye feature. At 19/1800 UTC Typhoon Omais responded to the weakening ridge to the northeast by decelerating to 5 kts and turning towards the north- west. Six hours later, the MSW dropped to 60 kts, and Omais was down- graded to a tropical storm while located approximately 390 nm south- southwest of Okinawa. A 19/2252 UTC SSM/I pass revealed a partially- exposed LLCC on the north side of the deep convection. At 0600 UTC on 20 May Tropical Storm Omais turned north-northeastward, completing its recurvature and accelerating to around 12 kts. The MSW dropped rather quickly through the 20th and was barely of tropical storm strength by 0000 UTC the next day. Continuing to the north and north- northeast, the storm blew itself out at 22/0600 UTC when located 380 nm southwest of Iwo Jima. An extract from JTWC's final warning, issued at this time, concluded: "TD-06W has dissipated more rapidly than previously forecast. Animated multi-spectral and enhanced infrared satellite imagery indicates an area of convection with no identifiable low-level circulation center." The remnants eventually merged with a frontal system. JTWC was the only warning agency to classify Omais as a typhoon, and JMA was the only other agency to upgrade the system to severe tropical storm status, i.e., winds greater than 48 kts. JMA's peak 10-min avg MSW was 50 kts with an estimated minimum CP of 985 hPa. The peak 10-min avg MSW estimated by NMCC and CWB was 40 kts, and the peak intensity from PAGASA was 35 kts during the time Omais/Enteng was within that agency's AOR. The cyclone remained outside HKO's area of warning responsibility throughout its entire lifetime. D. Damage and Casualties ------------------------ No damage or casualties are known to have resulted from Typhoon Omais. (Report written by Kevin Boyle) ************************************************************************* NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for May: 1 tropical cyclone of gale intensity 1 tropical cyclone of hurricane intensity Sources of Information ---------------------- Most of the information presented below is based upon tropical cyclone warnings and significant tropical weather outlooks issued by the Joint Typhoon Warning Center of the U. S. Air Force and Navy (JTWC), located at Pearl Harbor, Hawaii. Occasionally some information may be gleaned from the daily tropical weather outlooks and other bulletins issued by the Indian Meteorological Department (IMD), which is the World Meteorological Organization's Regional Specialised Meteorological Centre (RSMC) for the basin. The reported maximum sustained winds (MSW) are based on a 1-minute averaging period, which is used by all U. S. civilian and military weather services for tropical cyclone warnings. For synoptic observations in the North Indian Ocean region, both 10-minute and 3-minute average winds are employed, but IMD makes no attempt to modify the Dvorak scale for estimating tropical cyclone intensity; hence, a 1-minute average MSW is implied. In the North Indian Ocean basin JTWC usually does not initiate warnings until a system has become well-organized and likely to attain tropical storm status within 48 hours. North Indian Ocean Tropical Activity for May -------------------------------------------- The spring tropical cyclone season got underway on schedule in the North Indian Ocean with Tropical Cyclone 01A (designated ARB0401 by IMD) forming early in the month just off the southwestern Indian coast. TC-01A moved erratically for several days, then began to move on a north- westerly trajectory paralleling the Indian coastline. Based on JTWC's analysis, the system peaked at 45 kts, but both IMD and the Pakistani Meteorological Department classified ARB0401 as a severe cyclonic storm, implying a MSW exceeding 48 kts. The second cyclone of the month, Tropical Cyclone 02B (designated BOB0401 by IMD), formed south of Calcutta and then moved east-northeastward, reaching hurricane intensity and smacking into the northwestern coast of Myanmar where it was quite destructive. Reports on both these cyclones follow. (A little explanation on IMD's cyclone numbering scheme may be in order. The numeric part is identical in format to JMA's scheme for the Northwest Pacific basin: 'yynn' where 'yy' represents the last two digits of the year and 'nn' is the storm's sequential number in the basin. IMD distinguishes between Arabian Sea systems (ARB) and those forming in the Bay of Bengal (BOB). Separate sequence numbers are used for each sub-region, whereas JTWC uses one numbering scheme for both regions combined, but of course uses different suffixes for the Arabian Sea and Bay of Bengal.) TROPICAL CYCLONE (TC-01A / ARB0401) 5 - 10 May -------------------------------------- A. Storm Origins ---------------- During the closing days of April an area of convection formed in the southern Bay of Bengal and tracked westward into extreme southern India. JTWC at one point assigned a fair development potential to this system, but no TCFA was issued, and to the author's knowledge, the system was not classified as a tropical depression by IMD. By 0400 UTC on 4 May the system lay overland approximately 500 km west of Madras, India. At the same time a new area of convection had developed in the Arabian Sea roughly 150 nm northwest of Cochin, India. Animated multi-spectral imagery revealed that convection had rapidly increased and a large CDO feature had formed. The existence of a well-defined LLCC was difficult to establish due to the extensive area covered by the CDO feature, but the new LLCC was forecast to become the dominant circulation within the larger disturbance. A TCFA was issued a few hours later at 1300 UTC, placing the center approximately 230 nm west-northwest of Cochin. The MSW was estimated at 25-30 kts, and deep convection had begun to consolidate around the developing LLCC. B. Synoptic History ------------------- JTWC issued the first warning on TC-01A at 0000 UTC on 5 May, placing the center approximately 200 nm west-northwest of Cochin, or about 450 nm south of Bombay. The MSW was estimated at 30 kts, and this was increased to 35 kts six hours later. Initial motion was very slow toward the west or west-northwest as TC-01A was trapped in a very weak steering environment. Indeed, the system spent the better part of the next three days wandering aimlessly around just off the southwest Indian coast. The track during this period looks like a tangled strand of cooked spaghetti. Deep convection continued to consolidate over the LLCC, but did so very slowly, at times being cyclic in nature. Thus, TC-01A was very slow to intensify. The estimated MSW had reached 40 kts by 06/0600 UTC, and the winds climbed to their peak of 45 kts at 0000 UTC on the 7th, based on satellite CI estimates of 45 and 55 kts. TC-01A at this time was located approximately 400 nm due south of Bombay, and had begun to move a little faster toward the north-northwest. Deep convection was still displaced slightly west of the partially-exposed LLCC. A little northward progress was made late on the 6th and early on the 7th, but at 07/1800 UTC the center of TC-01A was relocated about 90 nm to the east-southeast of the 1200 UTC position. For about 18 hours the cyclone moved slowly and erratically, then began to track at an increased pace toward the northwest due to the influence of a low to mid-level steering ridge building in from India. As late as the 08/1800 UTC warning, the intensity forecast called for TC-01A to reach hurricane intensity. However, drier air flowing from the northwest plus moderate vertical shear put the brakes on the cyclone's intensification process. Unfortunately, I do not have the 09/0000 UTC warning, but by 09/0600 UTC the MSW had been reduced to 35 kts, and recent microwave and multi- spectral satellite imagery indicated a weaker LLCC with a large mass of convection located to the northwest of the center. Some modest strengthening was forecast, but this failed to materialize. At 09/1200 UTC TC-01A was centered roughly 200 nm southwest of Bombay, and the LLCC had become weaker and more elongated. Convection continued to decrease and by 1800 UTC the mid-level circulation had become decoupled from the weak LLCC. JTWC issued the final warning on TC-01A at 0000 UTC on 10 May, locating the system approximately 220 nm west of Bombay. The mid-level circulation was still discernible, but no LLCC could be identified. (Note: The meteorological departments of India and Pakistan classified TC-01A as a 'severe cyclonic storm', which implies winds in excess of storm force (48 kts).) C. Meteorological Observations ------------------------------ I received from Huang Chunliang some rainfall measurements from southern India resulting from the Bay of Bengal low-pressure area (mentioned in Section A above). This system was designated as invest area 91B by Monterrey NRL, and was classified as a well-marked low pressure area by IMD, who considered it as part of the pre-storm stage to Severe Cyclonic Storm ARB0401 (TC-01A). (A thanks to Chunliang for sending the data to me.) (1) Sri Lanka - 02/0600 UTC to 03/0600 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) ----------------------------------------------------------------------- Mannar 43413 8.98 N 79.92 E 3 61.7 Trincomalee 43418 8.58 N 81.25 E 79 55.5 (2) India - 03/0300 UTC to 04/0300 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) ----------------------------------------------------------------------- Madras 43279 13.00 N 80.18 E 16 69.3 (3) India - 04/0300 UTC to 05/0300 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) ----------------------------------------------------------------------- Thiruvananthapuram 43371 8.48 N 76.95 64 52.8 (4) India - 05/0300 UTC to 06/0300 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) ----------------------------------------------------------------------- Thiruvananthapuram 43371 8.48 N 76.95 64 72.0 D. Damage and Casualties ------------------------ No damage or casualties are known to have resulted from Tropical Cyclone 01A. (Report written by Gary Padgett) TROPICAL CYCLONE (TC-02B / BOB0401) 17 - 19 May -------------------------------------- A. Storm Origins ---------------- Late on 14 May an area of convection developed approximately 475 nm south of Calcutta, India. Animated infrared satellite imagery indicated cyclic convection associated with an LLCC. The upper-levels were marginal for development with good poleward outflow but with moderate vertical shear. By 1800 UTC on the 15th the system was located about 445 nm south-southeast of Calcutta. The development potential was upgraded to fair as convection had become better organized over the LLCC. The peak winds were estimated at 20-25 kts. Twenty-four hours later the disturbance was centered about 285 nm south-southeast of Calcutta. Convection was still cyclic over the partially-exposed LLCC, although vertical shear appeared to have lessened a little since the previous day. JTWC issued a TCFA at 2200 UTC on 16 May, locating the center about 250 nm south-southeast of Calcutta. Animated enhanced infrared imagery indicated that convection was consolidating over the LLCC and that vertical shear continued to weaken. The maximum winds were then estimated at 25-30 kts. B. Synoptic History ------------------- The first JTWC warning on TC-02B, issued at 1200 UTC on 17 May, placed the center approximately 230 nm south of Calcutta with the MSW estimated at 35 kts. Twelve hours later the cyclone had drifted southwestward to a position almost 300 nm south-southwest of Calcutta. However, at 1200 UTC on the 18th TC-02B had reversed direction and was moving northeast- ward at 9 kts. Satellite CI estimates ranged from 35 to 55 kts, and based on these, JTWC upped the MSW slightly to 40 kts. By early on the 19th the cyclone had undergone a significant intensification. The MSW was increased to 60 kts, based on CI estimates of 65 kts, and the system was moving east-northeastward at 10 kts toward a rendezvous with the coastline of Myanmar. At 19/0000 UTC the center of TC-02B was located approximately 275 nm east-southeast of Calcutta, or about 60 nm west-southwest of Sittwe, Myanmar. The center of TC-02B made landfall near Sittwe around 19/0600 UTC. There was no JTWC warning at this hour, but the 1200 UTC warning estimated the MSW at 60 kts while noting that satellite CI estimates were 65 and 90 kts, so it seems quite likely that the cyclone was of hurricane intensity when it made landfall in Myanmar. The Indian Meteorological Department classified BOB0401 (its IMD designation) as a Very Severe Cyclonic Storm, which implies winds in excess of 65 kts. The final JTWC warning on TC-02B, issued at 19/1800 UTC, reduced the MSW to 30 kts and placed the weakening center inland near the city of Taurggyi, Myanmar. C. Meteorological Observations ------------------------------ There was a press report to the effect that winds of 85 kts were recorded in Myanmar when TC-02B made landfall, but I have no information as to whether this value was measured or estimated. Based on the resulting damage, and at least one satellite CI estimate of 90 kts near the time of landfall, winds of 85 kts are certainly plausible. Following are some rainfall amounts measured in association with TC-02B (BOB0401) sent by Huang Chunliang. A special thanks to Chunliang for sending the information. (1) Yunnan Province, China - 19/0000 UTC to 20/0000 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) --------------------------------------------------------------------- Ruili 56838 24.02 N 97.83 E 776 75.5 Lancang 56954 22.57 N 99.93 E 1054 63.8 Jinghong 56959 22.02 N 100.80 E 579 54.7 Dali 56751 25.70 N 100.18 E 1992 52.2 (2) Thailand - 19/0600 UTC to 20/0600 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) --------------------------------------------------------------------- Bhumibol Dam 48377 17.25 N 99.02 E 144 103.6 (3) Thailand - 19/1200 UTC to 20/1200 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) --------------------------------------------------------------------- Bhumibol Dam 48377 17.25 N 99.02 E 144 111.3 (4) Thailand - 19/1800 UTC to 20/1800 UTC Station WMO ID Lat Lon Alt (m) Rainfall (mm) --------------------------------------------------------------------- Bhumibol Dam 48377 17.25 N 99.02 E 144 112.4 Mae Sot 48375 16.67 N 98.55 E 197 108.4 D. Damage and Casualties ------------------------ Very Severe Cyclonic Storm BOB0401 (TC-02B) was quite destructive to Myanmar (formerly Burma). Press reports indicate that it was the most damaging cyclone to strike the nation since one in 1968. The storm caused tidal surges and flooding in the towns of Pauktaw, Myebon, Sittwe and Kyaukpyu in Rakhine State. The death toll stands at 140 with 139 of these occurring in Myebon. One report stated that 7 persons were missing, but another account placed the number missing at over 200 with many of these fishermen who were caught at sea when the cyclone struck. Over 18,000 persons were left temporarily homeless by the cyclone, and over 1000 houses were destroyed and almost another 1000 damaged. The storm left behind shortages of food and safe drinking water, and many telephone and power lines were downed. Several hospitals and health care centers were damaged, and many schools were damaged or destroyed. One report stated that over 300 head of cattle were killed in Myebon. The cyclone made landfall in northern Myanmar near the border with Bangladesh, and that nation experienced some fringe effects of the storm. High winds and torrential rains forced up to 50,000 people to evacuate low-lying homes and seek shelter in multi-level buildings. Five fishermen were reported missing after their two boats capsized off Cox's Bazar. The storm also blew down many trees and electricity poles in the area. The tropical cyclone followed a heat wave which had seen temperatures soar to 41 C, resulting in 21 deaths across Bangladesh during the month of May. (A special thanks to Matthew Saxby for sending me the press report about the cyclone's effects in Bangladesh.) Additional articles on the effects of this cyclone may be found at the following link: http://www.reliefweb.int/w/rwb.nsf/vLND> (Report written by Gary Padgett) ************************************************************************* SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E Activity for May: 1 severe tropical storm Sources of Information ---------------------- The primary sources of tracking and intensity information for Southwest Indian Ocean tropical cyclones are the warnings issued by the Tropical Cyclone Warning Centre on La Reunion Island, part of Meteo France (MFR), and the Regional Specialised Meteorological Centre for the basin. However, tropical cyclones in this region are named by the sub-regional warning centres on Mauritius and Madagascar with longitude 55E being the demarcation line between their respective areas of warning responsibility. The La Reunion centre only advises these agencies regarding the intensity of tropical systems. References to sustained winds imply a 10-minute averaging period unless otherwise stated. In the companion tropical cyclone tracks file, I occasionally annotate positions from warnings issued by the Joint Typhoon Warning Center (JTWC) of the U. S. Air Force and Navy, located at Pearl Harbor, Hawaii, when they differ from MFR's coordinates by usually 40-50 nm or more. The JTWC warnings are also the source of the 1-minute average maximum sustained wind values included in the tracks file. Additionally, information describing details of satellite imagery and atmospheric circulation features included in the narratives is often gleaned from the JTWC warnings. Southwest Indian Ocean Tropical Activity for May ------------------------------------------------ After a completely quiet month of April, the Southwest Indian Ocean gave one last gasp to close out the 2003-2004 cyclone season. Bulletins were issued by both MFR and JTWC for a tropical disturbance on 5 and 6 May with MFR numbering it as Tropical Disturbance 15 and JTWC designating it as TC-23S. The system weakened on the 6th and bulletins were discontinued by both agencies. After lying dormant for almost a week, the disturbance came to life rather quickly on the 12th and was named Tropical Storm Juba. Juba formed well to the southwest of Diego Garcia and pursued a poleward track, intensifying to near cyclone intensity and then quickly weakening. A report on Severe Tropical Storm Juba follows. One other tropical system merited bulletins from MFR. This system, designated as Tropical Disturbance 16, was a weak LOW which traveled from the eastern extremity of the basin to a point near Diego Garcia. MFR never actually called this a 'tropical disturbance', but rather a 'zone of disturbed weather', which is the lowest notch on their totem pole of tropical classifications. Around 1200 UTC on 19 May the first bulletin placed a weak center about 800 nm west-northwest of the Cocos Islands, or a like distance east-northeast of Diego Garcia. Bulletins were issued sporadically for the next several days, the final one at 24/0600 UTC placing the weakening system about 200 nm southwest of Diego Garcia. Dvorak classifications from MFR remained at 1.5/1.5 for this entire period, and peak central winds were never estimated to have exceeded 15-20 kts, although winds to 25-30 kts were forecast for isolated locations well-removed from the center in the southern semi- circle. TROPICAL STORM JUBA (MFR-15 / TC-23S) 5 - 15 May --------------------------------------- Juba: contributed by Swaziland A. Storm Origins ---------------- On 2 May an area of convection formed approximately 750 nm east- northeast of Diego Garcia. Animated infrared satellite imagery revealed a poorly-organized circulation located in a broad region of troughing. Conditions appeared somewhat favorable for intensification: vertical shear was marginal, there was good diffluence aloft, and a near- equatorial westerly wind burst was enhancing the system. A couple of days later the main area of interest was located about 685 nm east of Diego Garcia. A large CDO had developed in the vicinity of a possible LLCC and a recent QuikScat pass revealed an elongated circulation. However, a 03/2322 UTC TRMM pass had not shown any evidence of a LLCC. An upper-level analysis indicated that the developing LLCC was located equatorward of the subtropical ridge with favorable diffluence in the poleward direction, and the maximum winds were estimated at 20-25 kts near the center. JTWC upgraded the potential for development to fair in an interim STWO at 04/0400 UTC. Deep convection continued to be cyclic in nature throughout the remainder of the 4th and into the 5th. At 05/0700 UTC JTWC relocated the disturbance to a point approximately 300 nm east-southeast of Diego Garcia. Deep convection was displaced to the southwest of the center by moderate east-northeasterly vertical shear. JTWC issued a TCFA for the LOW at 05/1000 UTC, relocating the center about one degree north to a position about 270 nm east-southeast of Diego Garcia. Deep convection had begun to consolidate around the LLCC, and the system exhibited good poleward outflow. The MSW was estimated at 30 kts by JTWC. At 1200 UTC MFR issued the first bulletin on Tropical Disturbance 15. Concurrently, JTWC issued their first warning on TC-23S with 35-kt winds (1-min avg). The system was located about 225 nm east-southeast of Diego Garcia and was moving westward at 11 kts. B. Synoptic History ------------------- This tropical disturbance had two distinct "lives" separated by a period of five days. During the first phase of its life, TC-23S was unnamed--the name Juba was applied when it rapidly re-intensified on 12 May. On the 5th and 6th of May the system tracked slowly westward well to the east of Diego Garcia, guided by a low to mid-level ridge to the south. Intensification was forecast to be slow--poleward outflow was good, but the benefits of this were offset somewhat by moderate shear from the northeast. At 06/0600 UTC the center was relocated to the north of the previous position. Visible and QuikScat imagery revealed a fully-exposed LLCC to the northeast of the deep convection. Six hours later, JTWC issued their final warning (for Round #1) on TC-23S, placing the center about 130 nm east of Diego Garcia. Micro- wave imagery revealed that the LLCC had decoupled from the convection and was moving northeastward. MFR issued bulletins for another 12 hours, but also dropped the system after 07/0600 UTC when the weak LLCC was located about 350 nm east of Diego Garcia. During the first phase of Tropical Disturbance 15's life, the system was never classified as a tropical depression, i.e., the maximum 10-min avg winds near the center were never estimated in excess of 25 kts. The tropical disturbance was not finished, however. Late on 7 May deep convection began to rebuild over the LLCC. An upper-level analysis indicated that the area was somewhat favorable for redevelopment with moderate vertical shear and fair outflow. At 1000 UTC on the 8th the weak LLCC was located approximately 410 nm east-southeast of Diego Garcia. Deep convection was cyclic, but by 1400 UTC had increased over the LLCC enough that JTWC upgraded the development potential to fair. However, by 1800 UTC on 9 May the deep convection had diminished and the LLCC had become elongated, so the potential for development was downgraded to poor. The system at this point was located approximately 220 nm southeast of Diego Garcia, moving west-southwestward. Little change in the system's structure occurred on the 10th, but by 1800 UTC on 11 May the LLCC had reached a position about 160 nm southwest of Diego Garcia and convection was once more increasing in organization around the LLCC. There was still some easterly shear, but poleward outflow was good and the development potential was once more upgraded to fair. The system had by this time begun moving to the south. MFR began issuing bulletins on Tropical Disturbance 15 once more at 0600 UTC on 12 May, placing the center about 300 nm southwest of Diego Garcia. The 10-min avg MSW was given as 25 kts, and six hours later was upped to 30 kts, thereby according tropical depression status to the system. (In the Southwest Indian Ocean basin, a system must have 10-min avg winds of 30 kts to be classified as a tropical depression.) At 12/1800 UTC the center was located approximately 350 nm southwest of Diego Garcia, and recent microwave imagery showed a well-defined LLCC beneath the deep convection. JTWC upped the potential for development to good, and MFR upgraded the system to a 45-kt tropical storm with the Meteorological Services of Mauritius assigning the name Juba. JTWC soon followed with a warning at 2100 UTC which estimated the MSW at 35 kts (1-min avg). (Note: When Juba was named, some confusion resulted since some versions of the list of names for the Southwest Indian Ocean basin gave the name as 'Jubela'. According to Philippe Caroff, Chief Forecaster at MFR, at the WMO Region I committee meeting in 2001, when this particular list of names was selected, the English version of the list contained 'Jubela' while the French version listed 'Juba'. At the subsequent Region I committee meeting at Maputo, Mozambique, in 2003, the discrepancy was discovered by the representative from Madagascar. Since the name was contributed by Swaziland, that nation's representative was consulted, and it was determined that the correct name was 'Juba'. Thanks to Philippe for sending me the explanation of this matter.) After all the effort that Juba had made to gain tropical storm status, its lifetime as a named storm was rather short and uneventful. It quickly strengthened to near tropical cyclone (hurricane) status, and then quickly weakened as it moved southward and then westward over the central South Indian Ocean, being steered along the western periphery of a low to mid-level ridge to the east. Tropical Storm Juba strengthened rather quickly--winds reached their peak intensity of 55 kts (10-min avg) at 13/1200 UTC, only 18 hours after the system had been upgraded to tropical storm status. At 13/1800 UTC JTWC upped the MSW (1-min avg) to 65 kts--in close agreement with MFR's 10-min avg. Juba was located about 400 nm northeast of Rodrigues Island at this juncture. After reaching its peak intensity, Juba began to weaken rapidly. By 14/0600 UTC the LLCC had become decoupled from the deep convection, and at 1800 UTC both MFR and JTWC downgraded Juba to depression status. (Interestingly, satellite CI estimates ranged from 25 to 55 kts.) The final MFR bulletin, issued at 15/0600 UTC, placed the dissipating LLCC about 275 nm north-northeast of Rodrigues. C. Damage and Casualties ------------------------ There are no known damage or casualties resulting from Severe Tropical Storm Juba. (Report written by Gary Padgett) ************************************************************************* NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E Activity for May: No tropical cyclones ************************************************************************* NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E Activity for May: No tropical cyclones ************************************************************************* SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E Activity for May: 1 hybrid depression South Pacific Tropical Activity for May --------------------------------------- No tropical cyclones formed during the late-season month of May in the South Pacific basin. Fiji did issue gale warnings on a system on 2 and 3 May, but no "F" number was assigned, and after the first bulletin at 02/0000 UTC, the system was referred to only as a 'depression' and not a 'tropical depression'. The LOW was most likely either hybrid or non-tropical in nature. The system formed near 22.0S/154.0W and remained quasi-stationary in the area for about 24 hours. Peripheral gales of up to 40 kts were forecast in association with the depression. ************************************************************************* 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 from the archive sites listed below. (Note: I do have a limited e-mail distribution list for the track files. If anyone wishes to receive these via e-mail, please send me a message.) 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. Back issues can be obtained from the following websites (courtesy of Michael Bath, Michael V. Padua, Michael Pitt, and Chris Landsea): http://australiasevereweather.com/cyclones/> http://www.typhoon2000.ph> http://mpittweather.com> ftp:// ftp.aoml.noaa.gov/hrd/pub/landsea/padgett/> 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: http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html> TROPICAL CYCLONE REPORTS AVAILABLE JTWC now has available on its website the complete Annual Tropical Cyclone Report (ATCR) for 2002 (2001-2002 season for the Southern Hemisphere). ATCRs for earlier years are available also. The report for the 2002-2003 Southern Hemisphere season has also recently been added. The URL is: http://199.10.200.33/jtwc.html> Also, TPC/NHC has available on its webpage nice "technicolor" tracking charts for the 2003 Atlantic and Eastern North Pacific tropical cyclones; also, storm reports for all the 2003 Atlantic and Eastern North Pacific cyclones are now available, as well as track charts and reports on storms from earlier years. The URL is: http://www.nhc.noaa.gov> A special thanks to Michael Bath of McLeans Ridges, New South Wales, Australia, for assisting me with proofreading the summaries. PREPARED BY Gary Padgett E-mail:[email protected] Phone: 334-222-5327 Kevin Boyle (Eastern Atlantic, Western Northwest Pacific, South China Sea) E-mail:[email protected] Huang Chunliang (Assistance with Western Northwest Pacific, South China Sea) E-mail:[email protected] Simon Clarke (Northeast Australia/Coral Sea, South Pacific) E-mail:[email protected] ************************************************************************* *************************************************************************

[8]ページ先頭