GARY PADGETT'S MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY MAY, 2001 (For general comments about the nature of these summaries, as well as information on how to download the tabular cyclone track files, see the Author's Note at the end of this summary.) SPECIAL NOTE: I have included the Glossary of Abbreviations and Acronyms at the end of this summary. New acronym added: TCFA - Tropical Cyclone Formation Alert *********************************************************************** MAY HIGHLIGHTS --> Intense Arabian Sea cyclone threatens west coast of India --> Most intense May Eastern Pacific hurricane on record forms *********************************************************************** ***** Feature of the Month for May ***** RESULTS OF TROPICAL CYCLONE SURVEY - PART 1 SIZE AS A POSSIBLE CLASSIFICATION CRITERION A few months ago I sent a little survey to several persons whom I either knew personally or else had corresponded much with over the past three years that I've been writing the global tropical cyclone summaries. The following were the ones who responded, and to them I would like to extend a special thanks for taking the time to reply: Jeff Callaghan, Steve Ready, Matthew Saxby, Philippe Caroff, James Franklin, David Roth, Jack Beven, Chris Landsea, Julian Heming, and Rich Henning. The survey was a solicitation of opinions regarding certain issues relevant to the classification of tropical cyclones, especially focusing on borderline type systems which in some basins may be readily treated as tropical cyclones and not in others. The questions that I asked in the survey were as follows (slightly reworded): (1) Regarding subtropical cyclones or otherwise hybrid systems: How "tropical" should one be before being classified as a tropical cyclone? (2) Regarding spatial distribution of gales: In how many quadrants and how close in to the center should gales be occurring before a system is named as a tropical storm (or cyclone)? (3) Should monsoon depressions with gale-force winds be considered tropical storms (or cyclones)? (4) Should the (usually) small TUTT-generated systems of higher latitudes be considered tropical cyclones? (5) Regarding extremely small midget systems: Should there be a size criterion for classification as a tropical cyclone? All the tropical cyclone warning agencies have official terminology and operational procedures which work well in their respective areas of responsibility, and issuing timely and accurate warnings in real time is certainly the primary goal of all warning centers. But the study of tropical cyclones from a climatological and statistical perspective and with a global scope is also very important, even if secondary to the operational warning side of things. And such study is quite often hampered because of inconsistencies in the manner in which the above types of systems are treated between the various warning centers (or sometimes even by a given center). My purpose was to try to get a little dialogue going regarding some of those issues which I have come to perceive as "sticking points" that need some sort of consensus if the goal of a reasonably consistent global definition of a tropical cyclone is ever to be attained. I am concerned here with systems whose winds have reached gale intensity (34 kts or higher) and normally would be assigned names as tropical storms (tropical cyclones in WMO Region 5) by the responsible warning center (except of course in the North Indian Ocean). These are the systems which are normally archived in databases by the various meteorological agencies and are, in a sense, the ones "remembered" by posterity. My plan is to utilize the responses I have received as material for my Feature of the Month articles for about three months. However, if anyone else has an opinion they'd like to share on any of the above questions, I'd be happy to hear from them and will include their responses in with the others. For this month I am limiting the discussion to the last question: Should there be an arbitrary size criterion for classification as a tropical cyclone? Several of the respondents wondered why I'd even asked that question. Admittedly, the size of a system is for the most part a non-issue. But that question was raised many years ago in the excellent annual summary article for the Eastern Pacific hurricane season of 1971 written by William J. Denney, then of the NWS Forecast Office in San Francisco. (The article was published in Monthly Weather Review, Volume 100, Number 4, April, 1972.) In his discussion of Tropical Storm Katrina, which was a very small, tightly-wound tropical storm that in its early stages apparently had the magnitude of a meso- cyclone, Mr. Denney pointed out that some storms seen in the Eastern Pacific during the previous years since the advent of satellites had gale-wind areas as small as 15 nm in diameter. He briefly discussed the issue of whether there should be an arbitrary size definition to distinguish the "ministorm" from the normal-sized tropical cyclone, mainly because of the difficulty of following such small storms as Katrina. However, his conclusion was that, instead of instituting a size criterion for tropical cyclones, the problem might better be considered a challenge to the improving skill and technology of applied meteorology. Australia has an outstanding example of what a midget tropical cyclone can do: Cyclone Tracy, which practically obliterated the city of Darwin in December, 1974. According to information received from Jeff Callaghan, Tracy's gale radius was only about 18 nm. Other very small but intense tropical cyclones which have struck Australia were Kathy (1984) with a gale radius of 35 nm, and Ada (1970) with a gale radius of 30 nm. And as Matthew Saxby pointed out, Tropical Cyclones Steve (2000) and Rona (1999), both of which caused significant damage, were midgets. The most intense hurricane known to strike the United States during the past century-and-a-half was also a very small tropical cyclone. The famous Labor Day Hurricane which struck the Florida Keys in 1935 produced the lowest pressure ever recorded on land in the Western Hemisphere: 892 mb. (The only lower measured pressure in an Atlantic hurricane was the 888 mb reading obtained from a dropsonde in the eye of Hurricane Gilbert in September, 1988.) The 1935 hurricane caused incredible structural damage, especially to the trestles and bridges of Henry Flagler's railroad to Key West. Engineers have estimated that winds from 175 to 220 kts would have been required to have caused some of the observed damage. According to Rich Henning, the gale radius of that hurricane was on the order of 25-30 nm. The eye passed through the middle Keys but neither Miami nor Key West reported gale force winds. Over 400 persons died in the hurricane. Many were literally sandblasted to death and found with no skin and no clothes except for belt and shoes. (The last sentence found in Dunn & Miller's _Atlantic Hurricanes_.) None of the responses I received were in favor of an arbitrary size criterion. David Roth wrote: "Midget phases of a tropical cyclone's life should be treated as just that--a phase they occasionally go through." Chris Landsea and Jack Beven both suggested some criteria that might be applied to extremely small systems. Chris suggested that a very small system should have some persistence, lasting at least a day or two. If the system is (as Chris put it) "a flash-in-the-pan, it may be that it was more of a mid-tropospheric mesoscale convective vortex and not a true tropical cyclone." Jack was the only person who suggested any spatial dimensions that might be considered for defining a tropical cyclone. He writes: "My view is that the smallest size of a tropical cyclone would be something somewhat larger than a mid-western supercell mesocyclone--roughly 10-20 nm or so in diameter. I think the tropical cyclone has to be large enough that the circulation is driven by multiple convective cells, as would be the case if an eyewall or spiral band is present." So, in summary, it appears that there is a consensus that size should not be a criterion in defining a tropical cyclone. For the June Feature I'll try to tackle synopsizing the opinions I received on the subject of subtropical/hybrid cyclones, for which there does not exist a general consensus regarding how to classify such systems. *********************************************************************** ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for May: 1 possible subtropical cyclone Atlantic Tropical Activity for May ---------------------------------- No tropical cyclones formed in the month of May in the Atlantic basin, which is typical. Since 1886 twelve tropical storms have been tracked in the Atlantic basin during May, three of which reached hurricane intensity. The last May tropical storm was Arlene in 1981, and the last hurricane in May was Alma in 1970. Several other years have seen tropical depressions or subtropical systems develop during May. In May of 2001, a low-pressure area formed along an old stationary front on the 5th in the Bahamas, roughly 200 nm north of the extreme eastern tip of Cuba, and moved east-northeastward. By late on the 5th convection had wrapped around the eastern and northern quadrants of the LOW. By the morning of the 6th, the cyclone had an occluded appearance with sporadic convection just north and well to the east of the center due to dry air wrapping around its south side. Later on the 6th and into the 7th, the center became devoid of convection and the low-level swirl drifted southwestward as its upper-level circulation warmed and weakened. Late on the 5th and throughout the 6th, this cyclone was not connected to any frontal cloudiness on satellite imagery. That fact, plus the fact that convection was close to the center on the 5th and 6th, led to the conclusion that the LOW was very possible subtropical in nature. Temperature gradient was minimal at best around the system, though it had a decent dewpoint contrast. Most of the high winds were north and west of the center in the Bahamas and southwest Atlantic in a region of good pressure gradient between the LOW and a HIGH in the eastern U. S. A cold front dropped in from the north late on the 7th and early on the 8th, spawning a new area of low pressure which swept this cyclone to the east, absorbing it during the morning on the 8th. A track for this system follows. Since this was not a tropical cyclone, I am not going to add the track to the May tracks file and re-distribute that, but I will include it in the cyclone tracks file for June. All the information and the track for this system was supplied by David Roth of the Hydrometeorological Prediction Center in Maryland. A special thanks to David for providing the information. *********************************************************************** Storm Name: None Cyclone Number: None Basin: ATL (Possible subtropical storm--track supplied by David Roth.) Date Time Lat Lon Cent MSW MSW Remarks (GMT) Press 1-min 10-min (mb) (kts) (kts) ----------------------------------------------------------------------- 01 MAY 05 0600 23.0 N 74.0 W 1008 20 01 MAY 05 1200 23.2 N 72.9 W 1007 25 01 MAY 05 1800 23.8 N 72.2 W 1007 30 01 MAY 06 0000 24.8 N 71.7 W 1007 30 01 MAY 06 0600 25.2 N 71.0 W 1006 30 01 MAY 06 1200 25.0 N 70.2 W 1005 30 01 MAY 06 1800 24.5 N 70.1 W 1004 35 01 MAY 07 0000 24.0 N 71.0 W 1004 40 01 MAY 07 0600 24.0 N 69.8 W 1005 45 01 MAY 07 1200 24.2 N 68.8 W 1005 45 01 MAY 07 1800 24.5 N 67.9 W 1006 45 01 MAY 08 0000 25.2 N 67.3 W 1006 45 01 MAY 08 0600 26.0 N 67.0 W 1006 40 Note: The winds and pressures used were based on ship reports and analyses prepared by HPC and MPC. Note that the maximum sustained winds held constant at gale force until dissipation due to the formation of another LOW to its north. Errors on the center location should be between 30 and 60 nautical miles. *********************************************************************** NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for May: 1 hurricane NOTE: Much of the information presented below was obtained from the TPC/NHC discussion bulletins issued with every regular advisory (CPHC for locations west of 140W.) All references to sustained winds imply a 1-min averaging period unless otherwise noted. Northeast Pacific Tropical Activity for May ------------------------------------------- Over the thirty years from 1971-2000, the first tropical storm of the season in the Northeast Pacific basin has developed in May thirteen times, or in 43% of all seasons. The first hurricane, however, has formed in May on only 7 occasions, or 23% of the time. The first intense hurricane (i.e., reaching Category 3 or higher on the Saffir/ Simpson scale) had never formed in May since the advent of satellites. The year 2001 changed that statistic: Hurricane Adolph became the first Category 3 Eastern Pacific hurricane on record on 28 May when its MSW reached an estimated 105 kts--24 hours later Adolph had become the first May Category 4 hurricane on record in the North Pacific east of the Dateline. Very fortunately for the Mexican coastline, Adolph remained at sea with only rainbands and heavy surf affecting the coast. The summary on Adolph following was written by John Wallace of San Antonio, Texas. A very special thanks to John for his assistance. Hurricane Adolph (TC-01E) 25 May - 2 June -------------------------- A. Origins ---------- The tropical LOW that became Adolph formed along the axis of a tropical wave, one that lingered in the Pacific west of Central America for several days. Indeed, the UKMET had forecast tropical storm development there as early as the 20th, long before there was any hint of cyclogenesis. The progenitor disturbance organized slowly but surely, and the JTWC/NPMOC issued a TCFA for the LOW at 0200 UTC on the 25th. Visible satellite imagery, along with scatterometer data, supported the LOW's upgrade to Tropical Depression One-E at 2100 UTC on 25 May. At this time it was located roughly 200 nm south-southwest of Acapulco, Mexico. Though conditions were favorable for intensification, One-E was slow to strengthen; it did not become a tropical storm for a full day after the first advisory was issued. The center was occasionally difficult to pinpoint, and the depression's organization waxed and waned. Nevertheless, One-E was upgraded to Tropical Storm Adolph at 2100 UTC on 26 May, located roughly 175 nm south-southwest of Acapulco. It was then that Adolph's previously humble existence made a dramatic turnaround. B. Track and Intensity History ------------------------------ Adolph intensified swiftly after its upgrade, reaching hurricane strength only 24 hours later, at 2100 UTC on 27 May, some 185 nm south of Acapulco. It attained a 105-kt MSW just six hours later. Adolph initially deepened at an impressive rate: 1.46 mb per hour, between its upgrade and 0300 UTC on the 28th. Intensification continued until Adolph reached its peak MSW of 125 kts at 0300 UTC on 29 May with an estimated CP of 940 mb. At this time it was located roughly 200 nm south-southwest of Zihuatanejo, Mexico. Adolph had a well-defined eye, and its cold CDO began to take on a so-called "buzzsaw" appearance characteristic of very strong hurricanes. According to the NHC, raw Objective Dvorak Numbers were as high as T7.0, which is equivalent to a MSW of 140 kts. An SSMI pass at 0416 UTC on the 29th clearly depicted a pair of concentric eyewalls. Adolph maintained its peak intensity for roughly eighteen hours. The cyclone, which had been previously meandering southeastward, began a turn to the north, then west-northwest, beginning late on the 27th. A mid-level ridge to its north built eastward, finally providing a steady steering current and a moderate rate of motion. Adolph was at first a slow-mover; at 1500 UTC on the 28th, some three days after the first advisory, Adolph was only 51 nm from its first warning position. That being said, the change in its track warranted the issuance of watches and warnings for the Mexican coast. A tropical storm warning and a hurricane watch were issued for the coast at 0300 UTC on the 28th, extending from Acapulco westward to Lazaro Cardenas. The hurricane watch was dropped at 2100 UTC on the 28th, though Adolph continued to roughly parallel the coast. The tropical storm warning was dropped on the next advisory, at 0300 UTC on the 29th, as Adolph reached peak intensity. A slow weakening trend began at 2100 UTC on the 29th, though outflow remained good. At first, the weakening was due to an eyewall replacement cycle; soon after that, though, cooler SSTs along the storm's track began to take their toll. Adolph's cloud tops warmed, and convection decreased in areal extent; by 1500 UTC on the 30th the MSW had dropped below 100 kts. Stable air-entrainment exacerbated the process. The cyclone assumed a more westward track on the 31st, and its deterioration accelerated. The slight track change was no doubt due to the increasing influence of low-level winds from a ridge to its north. The cyclone passed about 125 nm south of Socorro Island around 1500 UTC on 31 May at minimal hurricane intensity, then, by 2100 UTC, Adolph had weakened to tropical storm strength and its forward motion had decreased. Ship reports suggested that the storm's circulation was becoming distorted. At 2100 UTC on 1 June the convection-free vortex was downgraded to a depression. The last advisory on Tropical Depression Adolph was issued at 0300 UTC on 2 June when it was located 500 nm west-southwest of Manzanillo. A remnant swirl of low clouds persisted for a few days thereafter. C. Historical Tidbits --------------------- Adolph was far and away the most intense May hurricane on record in the Northeast Pacific basin. It is interesting to note that the previous recordholder for May was also a hurricane named Adolph back in 1983. The earlier Adolph peaked at 95 kts. And while on the subject of hurricanes named Adolph, the previous Hurricane Adolph, in 1995, reached a peak intensity of 110 kts, but that storm occurred in mid-June. This is also only the second time since 1971 that there have been two consecutive Northeast Pacific seasons with May hurricanes (2000-01, and 1983-84). D. Damage and Casualties ------------------------ Though rainbands from Adolph occasionally impinged on the Mexican coast--to say nothing of heavy surf--no casualties or damage are known to the author. *********************************************************************** NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for May: 1 tropical depression ** 1 tropical storm ** - No warnings were issued on this system by any warning center. The track and intensity estimates were provided by Roger Edson of the University of Guam, formerly a forecaster with JTWC. NOTE: Most of the information on each cyclone's history presented in the narrative will be based upon JTWC's advisories, and references to winds should be understood as a 1-min avg MSW unless otherwise noted. However, in the accompanying tracking document I have made comparisons of coordinates with JMA (Japan) and the Philippines (PAGASA) when their positions differed from JTWC's by usually 40-50 nm or more. A special thanks to Michael V. Padua, owner of the Typhoon 2000 website, for sending me the PAGASA and JMA tracks. In the title line for each storm I plan to reference all the cyclone names/numbers I have available: JTWC's depression number, the JMA-assigned name (if any), JMA's tropical storm numeric designator, and PAGASA's name for systems forming in or passing through their area of responsibility. Northwest Pacific Tropical Activity for May ------------------------------------------- The first named tropical storm of 2001 in the Northwest Pacific formed in mid-month in the South China Sea from a depression which had earlier trekked westward across the central Philippines from the Philippine Sea. While Cimaron was the first tropical storm to form in the current year, it was not the first storm on the charts. Back in early January Tropical Storm Soulik from late December, 2000, after weakening, suddenly flared up and became a rather intense, albeit brief, typhoon east of the Philippines. A report on Tropical Storm Cimaron is given below; however, there were a couple of other systems that warrant mention. Roger Edson forwarded me a track he'd generated for a tropical depression east of the Philippines. A very weak LOW was located far to the south of Yap on 16 May. The system drifted generally north- northwestward over the next couple of days, reaching a point about 100 nm north-northeast of Palau by 1200 UTC on 18 May. The STWO issued by JTWC at 18/0600 UTC mentioned the disturbance, which, according to Roger's track, likely had maximum winds of about 20 kts at the time. The STWO for 19 May upgraded the development potential to fair, and a Formation Alert was issued at 20/0100 UTC as convection was beginning to increase near the LLCC and a 200-mb analysis indicated diffluent flow aloft. The system by this time was moving northward a few hundred miles east of the Philippines, passing about 350 nm east of Catanduanes Island around 0000 UTC on the 21st, when, according to Roger's track, the peak intensity of 30 kts was reached. A second Formation Alert was issued by JTWC at 21/0100 UTC, but by 22/0000 UTC the system was weakening and becoming extratropical about 500 nm east of the northern tip of Luzon. (Roger's track for this system was included in the cyclone tracks file for May. A special thanks to Roger for sending me the information on this system.) The other disturbance formed in the South China Sea off the coast of Vietnam on 14 May. By 0600 UTC on the 15th a broad, fully-exposed LLCC was located about 170 nm southeast of Da Nang with convection sheared away toward the west. The system moved north-northwestward, roughly parallelling the Vietnamese coast. JTWC issued a Formation Alert at 1130 UTC on 16 May when the center was estimated to be about 140 nm northwest of Da Nang. Convection was increasing near the LLCC and the LOW was located in an environment of weak vertical shear with good outflow aloft. However, by 17/0530 UTC the system had moved onshore just east of Nam Dinh, Vietnam, so the Formation Alert was cancelled. The Central Weather Bureau of Taiwan did refer to this disturbance as a tropical depression in one of their bulletins--none of the other agencies classified it as a depression. (No track for this system was included in the cyclone tracks file for May. Huang Chunliang of Fuzhou, China, informed me that the Central Weather Bureau had classified this system briefly as a depression--thanks to Chunliang for alerting me to this fact.) Tropical Storm Cimaron (TC-03W / STS 0101 / Crising) 7 - 21 May ----------------------------------------------------- Cimaron: contributed by the Philippines, is the name of a Philippine wild ox A. Origins ---------- A STWO issued by JTWC at 1430 UTC on 4 May mentioned that a weak LLCC had developed in the monsoon trough about 40 nm south of Koror. A 200-mb analysis showed diffluent, moderate easterlies over the area. By the next day the disturbance had migrated (or re-formed) farther to the west to a position approximately 160 nm southeast of the Philippine island of Mindanao. A SSM/I pass revealed deep convection but a broad, weak LLCC; by 6 May the area was centered on the southern coast of Mindanao. JTWC issued a Formation Alert at 1200 UTC, relocating the center farther northward along the east coast of Mindanao. The LLCC was accompanied by persistent convection which was displaced to the north, and the system lay under weak to moderate upper-level easterlies on the equatorward side of a ridge of high pressure. JTWC issued the first warning on TD-03W at 07/0000 UTC, locating the ill-defined center about 75 nm east of the northern tip of Mindanao. The MSW was estimated at only 20 kts, based on satellite CI estimates of 25 kts, coastal synoptic reports of 10 kts, and a ship report of 20 kts. By 1800 UTC the depression was centered in the Leyte Gulf region, and over the next couple of days tracked west- northwestward across the central Philippines. At 08/1800 UTC, based on a synoptic analysis, the center was relocated about 73 nm south- southwest of the previous warning position to a point 160 nm southeast of San Pablo. At 0000 UTC on 9 May the depression's center was in the Sulu Sea, and by 1200 UTC had emerged into the South China Sea proper. During its trek across the Philippines the MSW remained set at 25 kts, though on an occasion or two CI estimates of 30 kts were received. The winds were upped to 30 kts at 09/0600 UTC when TD-03W's center was emerging into the South China Sea about 170 nm south-southwest of Manila. After moving out into the South China Sea, the system turned northward off the west coast of Luzon. CI estimates had reached 35 kts at 1800 UTC, but the MSW remained at 30 kts for that warning. However, at 0000 UTC on the 10th, JTWC upgraded TD-03W to a tropical storm with 35-kt winds (based on CIs of 35 and 45 kts) located 125 nm west- southwest of Manila. Also at 10/0600 UTC, PAGASA issued their first warning on the system as a tropical depression, naming it Crising (a Filipino nickname). It is very interesting that PAGASA didn't initiate warnings on 03W/Crising until it had reached tropical storm intensity per JTWC analysis, especially considering that it had trekked across the central part of the archipelago. Normally, with systems in the vicinity of the Philippines, PAGASA is the first agency to issue bulletins. JMA upgraded 03W/Crising to a tropical depression at 10/0600 UTC. B. Track and Intensity History ------------------------------ JTWC increased the MSW to 40 kts at 10/1200 UTC, but the intensity held steady at that level for 24 hours. Tropical Storm 03W/Crising moved slowly northward roughly 100 nm off the west coast of Luzon for about 36 hours until it turned more to the north-northeast at 11/1200 UTC. PAGASA and JMA upgraded the system to a tropical storm at 11/0000 UTC with JMA assigning the name Cimaron. The newly-named storm was then located about 70 nm west of Lingayen. Satellite-derived CI estimates had reached 45 kts, but based on synoptic reports, JTWC held the MSW to 40 kts; JMA and PAGASA were estimating 35-kt 10-min avg winds. At 1200 UTC on the 11th JTWC increased the MSW estimate to 45 kts; at 1800 UTC the center was relocated slightly to the south of the 1200 UTC position and was moving slowly north-northeastward. By 12/0000 UTC Tropical Storm Cimaron/Crising was located about 85 nm north-northwest of Port San Esteban and moving to the northeast at 4 kts. The storm appeared to have weakened some over the previous twelve hours due to increased vertical shear. Water vapor imagery showed the system to be interacting with a frontal boundary, and the cyclone was located poleward of an upper-level ridge axis in a region of moderate to strong vertical shear. At 0600 UTC JTWC decreased the MSW to 40 kts, based on CIs of 30 and 45 kts. By 1200 UTC the storm's center was about 105 nm north-northwest of Port San Vicente and moving northeastward at a slightly faster pace (12 kts). The weakening trend noted earlier proved to be temporary and at 1800 UTC the winds were increased once more to 45 kts with the storm in the Bashi Channel about 30 nm west of Itbayat Island. However, Cimaron was already beginning to show the first hints of what turned out to be a slow, prolonged transition into an extratropical cyclone. As Cimaron continued to slowly accelerate northeastward, passing a short distance southeast of the southern tip of Taiwan and into the southern Ryukyus, it continued to increase in intensity, reaching a peak of 60 kts at 1800 UTC on 13 May when it was centered about 25 nm south-southwest of Miyakojima Island. Vertical shear had weakened slightly and an upper-level jet stream to the north of the cyclone had helped to create an outflow channel to the northeast of the center. Cimaron was being steered northeastward by a low- to mid-level ridge to the southeast, and its forward motion gradually accelerated with the approach of a mid-latitude trough from the northwest. The cyclone was located about 80 nm southwest of Naha, Okinawa, at 0000 UTC on 14 May, moving northeastward at 17 kts. The estimated MSW was down slightly to 55 kts (based on CIs of 55 and 65 kts), and the convection was beginning to decouple from the LLCC with a partially- exposed center evident about 15 nm southwest of the deepest convection. The center of Cimaron passed over Okinawa around 14/0600 UTC with peak winds estimated at 45 kts, and by 1200 UTC the storm had become extra- tropical about 115 nm northeast of the island. The remnants of former Tropical Storm Cimaron continued as an extratropical gale for another week, initially moving east-northeastward through 17 May, then curving more to the northeast, reaching the vicinity of 160E by 19/0000 UTC. Thereafter, the LOW turned generally northward and moved slowly up the 160th meridian, being last mentioned (in JMA High Seas bulletins) as a separate entity at 21/0000 UTC near 45N, 158E. C. Meteorological Aspects ------------------------- As stated in the discussion above, JTWC intensity estimates were frequently based in part on synoptic reports from the Philippines and ships, but the details of those were not given. At the time Cimaron reached its peak intensity of 60 kts, Miyakojima Island (WMO 47927), located about 25 nm to the northeast of the center, reported a 1-min avg sustained wind of 39 kts. As the cyclone crossed Okinawa, Naha Airport (WMO 47936) reported a maximum 10-min mean wind of 30 kts. (The MSW at that time was estimated at 45 kts by both JTWC and JMA.) As Tropical Storm Cimaron/Crising passed near northwestern Luzon, Basco recorded 305 mm of rain in 48 hours (the monthly average is 129 mm). Also, Lan Yu, a small island located off Taiwan's south- eastern coast, recorded 262 mm of rain in 48 hours. (At 13/0000 UTC Cimaron's center was about 36 nm south-southeast of Lan Yu.) These rainfall observations were forwarded to the author by Patrick Hoareau; a special thanks to Patrick for sending them. Unfortunately, the exact dates/times of the relevant 48-hour periods are not available. D. Comparisons between JTWC and Other Centers --------------------------------------------- As noted above, Cimaron was one of the rare cases where JTWC "jumped the gun" on PAGASA as far as initiating tropical depression warnings was concerned. However, after PAGASA and JMA had begun issuing warnings on the system, the estimated intensities by those agencies compared rather well with JTWC's MSW. JMA's bulletins did not reflect the slight weakening reported by JTWC on 12 May, but the peak winds reported by the two centers--60 kts from JTWC and 50 kts (10-min avg) from JMA--were in excellent agreement. During the system's early stages as a tropical storm, there were some differences in center position estimates between the various agencies' warnings, but from 11/1200 UTC onward the coordinates were in remarkably good agreement. E. Damage and Casualties ------------------------ In spite of the heavy rainfall (and likely associated flooding) reported on northern Luzon, the author has been unable to locate any reports of significant damage or fatalities resulting from Tropical Storm Cimaron/Crising. *********************************************************************** NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for May: 1 tropical cyclone of hurricane intensity NOTE: The tracking and intensity information for North Indian Ocean Basin tropical cyclones is based primarily upon operational warnings from the Joint Typhoon Warning Center of the U. S. Air Force and Navy (JTWC) 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 WMO's RSMC for the basin. The MSW are based on a 1-min 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 region, both 10-min and 3-min average winds are employed, but IMD makes no attempt to modify the Dvorak scale for estimating tropical cyclone intensity; hence, a 1-min avg MSW is implied. In the North Indian basin JTWC usually does not initiate warnings until a system is well-organized and likely to attain tropical storm status within 48 hours. North Indian Ocean Tropical Activity for May -------------------------------------------- The first officially-declared tropical cyclone of 2001 in the North Indian Ocean basin developed in May in the Arabian Sea off the west coast of India and became one of the most, if not the most, intense cyclones on record in that region. Fortunately, the cyclone remained at sea and eventually weakened, sparing India what could have been a great disaster. In addition to writing the summary for Hurricane Adolph, John Wallace also wrote the summary for Tropical Cyclone 01A, and again, a big thanks to John for his help. (See the March and April summaries for discussions of two weaker systems which Roger Edson feels qualified as tropical storms in the eastern Bay of Bengal.) Tropical Cyclone (TC-01A) 21 - 28 May -------------------------- A. Origins ---------- The origin of TC-O1A can be traced back to a disturbance in the western Arabian Sea that was apparently first noticed on 18 May. A Tropical Weather Advisory issued at 1800 UTC on 19 May centered the disturbance east of the Yemeni island of Socotra and mentioned that it was quasi-stationary. Though it generated strong convection, the disturbance was amorphous with no closed circulation. There seemed to be no reason to suspect that it had anything other than meager prospects for development. On the 20th the situation improved for the disturbance, initially situated southwest of an upper-level trough, as an upper-level anticyclone developed over the system, providing good outflow. Though there was still no synoptic evidence of a closed circulation, there were the first definite hints of cyclonic structure in satellite imagery. The disturbance began a slow eastward track. By 1800 UTC on the 21st, the JTWC Tropical Weather Advisory indicated that a closed mid-level circulation had developed as the disturbance turned slightly north of east. Convection remained strong, and the disturbance's satellite presentation continued to improve. A surface circulation began to develop, and the JTWC issued a Formation Alert for the LOW at 0730 UTC on 21 May; the IMD first took notice of the disturbance at roughly the same time. The JTWC issued the first warning on Tropical Cyclone 01A at 1800 UTC on 21 May when it was located about 350 nm south-southwest of Mumbai (Bombay). Convective banding was developing in the cyclone's western semicircle and the system's organization was impressive. Located in a highly favorable environment, the stage seemed set for significant strengthening. Such was the case. B. Track and Intensity History ------------------------------ Intensification was initially rapid; TC-01A reached an intensity of 65-kts (1-min avg) at 1200 UTC on 22 May, just 18 hours after its upgrade, while located roughly 280 nm south-southwest of Mumbai. An incipient 12-nm eye was apparent in satellite imagery as early as 0600 UTC on the 22nd, twelve hours after its upgrade. Once the MSW reached 65 kts, the intensification rate slowed considerably, though it remained steady. This development coincided with the establishment of a ridge over southern India, which provided a southerly steering current. The northward turn was much more abrupt than forecast, sparing west India from a potential disaster. Storm force winds remained offshore as TC-01A briefly paralleled the coast. At 0000 UTC on the 23rd, the cyclone began a northwestward turn under the influence of another mid-level ridge centered over the northern Arabian Sea. By this time TC-01A had developed impressive outflow and intensification continued. The MSW reached an estimated 100 kts at 0000 UTC on 24 May, making TC-01A only the fourth Arabian Sea cyclone to reach that strength since 1975. It is worth noting that three of these four cyclones have formed since 1998. Tropical Cyclone 01A attained a peak MSW of 115 kts at 0600 UTC on 24 May while centered roughly 250 nm west-southwest of Mumbai. This makes TC-01A the strongest Arabian Sea cyclone since at least 1975. (NOTE: It's possible that the peak estimated MSW will be decreased to 110 kts in the JTWC's final best track, which would only tie the previous records.) The JTWC has traditionally applied the same scale used for Northwest Pacific tropical cyclones to North Indian Ocean cyclones; using this same wind-pressure relationship results in an estimated CP of 916 mb for TC-01A at peak intensity. However, this is pure conjecture; it's clear that the MSW is of primary importance in Dvorak analysis. The cyclone maintained its peak MSW for 18 hours; during this time the system presented a formidable satellite appearance, with an eye that was initially well-defined. However, the eye soon became indistinct as conditions became suddenly hostile. Easterly winds south of the upper-level ridge axis, in conflict with low- to mid-level westerlies, created substantial shear which began to rend the cyclone apart; its circulation was distorted and its convection weakened. This set the pattern that would continue for the rest of TC-01A's duration. Its forward speed decreased, and the cyclone became quasi-stationary on the 25th; a slow northward track commenced at roughly 1200 UTC on 26 May under the influence of a low- to mid-level ridge over India. Tropical Cyclone 01A weakened rapidly beginning at 0000 UTC on the 25th with the MSW dropping below 100 kts at 0600 UTC. At 0600 UTC on 26 May, just 24 hours later, it weakened to tropical storm strength while located about 300 nm west-southwest of Mumbai or 475 nm south- southeast of Karachi, Pakistan. The weakening trend slowed thereafter but did not stop. The final advisory on the cyclone was issued at 1800 UTC on 28 May with the center located some 175 nm west-northwest of Veraval. By this time TC-01A was a spiral of low clouds, devoid of deep convection. The cyclone's remnants made landfall in Gujarat on the 29th; unfortunately, no weather observations from the area were available to the author. C. Damage and Casualties ------------------------ The weakening and dissipation of Tropical Cyclone 01A came as a godsend to the province of Gujarat, still reeling from a deadly earth- quake in January. On top of that, local news agencies indicated that some communities were still living in the shadow of damage from 1998's TC-03A. That being said, the national and local governments mounted extensive and swift preparations for TC-01A's possible landfall. Kandla Port, one of the busiest in India, was closed for about four days. As many as 118,000 people were evacuated from coastal regions in India while another 50,000 were evacuated from high-risk areas of Pakistan. Casualty and damage information for the cyclone is either sparse or vague. Two hundred houses were washed away in two coastal villages on the 24th at Kosamba in the Valsad district. This is the only known damage on land. As for casualties, anywhere from 120 to as many as 900 fishermen were declared missing on the 24th according to local news reports. *********************************************************************** SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E Activity for May: No tropical cyclones *********************************************************************** 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: 2 tropical depressions ** ** - Both systems were hybrid, cold-cored systems rather than true tropical depressions. Most of the information presented below was taken from the operational warnings and advisories issued by the Fiji TCWC at Nadi. References to sustained winds imply a 10-minute averaging period unless otherwise noted. South Pacific Tropical Activity for May --------------------------------------- No named tropical cyclones formed in the South Pacific during May, but gale warnings were issued on two depressions, neither of which were tropical in nature, but rather were cold-cored, hybrid-type systems forming under strong shear aloft. The forecast gales were expected to develop in the systems' southern semicircles due to gradient compression as the LOWs moved into a strong ridge to the south. The first depression (14F) formed on 1 May about 225 nm west-northwest of Rarotonga, initially moved eastward, passing about 50 nm north of the island around 01/1800 UTC, and later accelerated off to the southeast. The final warning available to the author, issued by Wellington at 03/1200 UTC, placed the center about 550 nm southeast of Tahiti. The second depression (15F) formed on 7 May about 250 nm west-southwest of Tahiti, moved initially southward, then southeastward with the final warning issued by Fiji, at 09/1200 UTC, placing the center roughly 400 nm south-southwest of Tahiti. *********************************************************************** 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, but since the May, 2001 summary is shorter than average, I've appended the Glossary to the end following the Author's Note. *********************************************************************** AUTHOR'S NOTE: This summary should be considered a very preliminary overview of the tropical cyclones that occur in each month. The cyclone tracks (provided separately) will generally be based upon operational warnings issued by the various tropical cyclone warning centers. The information contained therein may differ somewhat from the tracking and intensity information obtained from a "best-track" file which is based on a detailed post-seasonal analysis of all available data. Information on where to find official "best-track" files from the various warning centers will be passed along from time to time. The track files are not being sent via e-mail. They can be retrieved in the following manner: (a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206] (b) Login as: anonymous (c) For a password use your e-mail address (d) Go to "data" subdirectory (Type: cd data) (e) Set file type to ASCII (Type: ascii) (f) Transfer file (Type: get remote_file_name local_file_name ) (The files will be named with an obvious nomenclature--using May as an example: may01.tracks) (g) To exit FTP, type: quit Both the summaries and the track files are standard text files created in DOS editor. Download to disk and use a viewer such as Notepad or DOS editor to view the files. The first summary in this series covered the month of October, 1997. If anyone wishes to retrieve any of the previous summaries, they may be downloaded from the aforementioned FTP site at HRD. The summary files are catalogued with the nomenclature: may01.sum, for example. Back issues can also be obtained from the following websites (courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael Pitt, and Rich Henning): OR Another website where much information about tropical cyclones may be found is the website for the UK Meteorological Office. Their site contains a lot of statistical information about tropical cyclones globally on a monthly basis. The URL is: TROPICAL CYCLONE REPORTS AVAILABLE JTWC now has available on its website the complete Annual Tropical Cyclone Report (ATCR) for 2000 (1999-2000 season for the Southern Hemisphere). ATCRs for earlier years are available also. The URL is: Also, TPC/NHC has available on its webpage nice "technicolor" tracking charts for the 2000 Atlantic and Eastern North Pacific tropical cyclones; also, preliminary storm reports for all the 2000 Atlantic and Eastern North Pacific cyclones are now available, as well as track charts and reports on storms from earlier years. The URL is: Prepared by: Gary Padgett E-mail: garyp@alaweb.com Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays) *********************************************************************** *********************************************************************** GLOSSARY of ABBREVIATIONS and ACRONYMS AOML/HRD - Atlantic Oceanographic and Meteorological Laboratory/ Hurricane Research Division, located on Virginia Key, Miami, Florida, U.S.A. AOR - area of responsibility CDO - central dense overcast CI - current intensity CIMSS - Cooperative Institute for Meteorological Satellite Studies (University of Wisconsin-Madison) CP - central pressure CPHC - Central Pacific Hurricane Center, Honolulu, Hawaii, U.S.A. FLW - flight level wind (or winds) FTP - file transfer protocol HPC - Hydrometeorological Prediction Center, Camp Springs, Maryland IMD - India Meteorological Department (RSMC New Delhi, India) JMA - Japanese Meteorological Agency (RSMC Tokyo, Japan) JTWC - Joint Typhoon Warning Center, formerly on Guam, now at Pearl Harbor, Hawaii kt - knot = 1 nautical mile per hour LLCC - low-level circulation center m - meter, or metre mb - millibar, numerically equivalent to hectopascal (hPa) MFR - Meteo France on Reunion Island mm - millimeter MSW - maximum sustained wind(s) (either 1-min avg or 10-min avg) nm - nautical mile = 6076.12 feet or 1852.0 meters NPMOC - Naval Pacific Meteorological and Oceanographic Center, Pearl Harbor, Hawaii, U.S.A. PAGASA - Philippines' Atmospheric, Geophysical & Astronomical Services Administration RSMC - Regional Specialized Meteorological Centre SST - sea surface temperature STS - severe tropical storm (MSW greater than 47 kts) STWO - Significant Tropical Weather Outlook - bulletin issued daily by JTWC giving information about various areas of disturbed weather and the potential for tropical cyclone development TC - tropical cyclone TCFA - Tropical Cyclone Formation Alert - issued by JTWC when a tropical cyclone is expected to develop within the next 24 hours TCWC - Tropical Cyclone Warning Centre (generic term) TD - tropical depression TPC/NHC - Tropical Prediction Center/National Hurricane Center, Miami, Florida, U.S.A. TS - tropical storm WMO - World Meteorological Organization, headquartered at Geneva, Switzerland UTC - Universal Time Coordinated, equivalent to Greenwich Mean Time or Zulu (Z) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 07.10.01 / Typhoon2000.com