GARY PADGETT'S MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY APRIL, 2005 (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.) ************************************************************************* APRIL HIGHLIGHTS --> Two tropical cyclones in South Indian Ocean --> Strong typhoon recurves east of Philippines ************************************************************************* ***** Feature of the Month for April ***** REVIEW OF GLOBAL TROPICAL CYCLONE TERMINOLOGY This month's feature is a repeat from several years back, last being included in the April, 2001, monthly summary. I have updated a few items based upon changes in basic definitions. The following is a synopsis of the operational terminology used by the various TCWCs to describe the different stages of tropical cyclone development and intensification. This gives the formal terminology used to refer to a given cyclone in warnings and advisories. For example, the Saffir/Simpson category is widely utilized in the U. S. to describe a hurricane's intensity, but the advisories do not refer to a hurricane formally as "Category Four Hurricane Xerxes" in the title line of the advisories. Also, in the U. S. the adjective "severe" may be frequently used to describe the character of a hurricane, but is not formally used as the descriptor for a given cyclone intensity range as it is in some basins. 1. ATLANTIC and NORTHEAST PACIFIC Basins - TPC/NHC (also CPHC) MSW Averaging Period: 1 minute Tropical Cyclone - generic term for systems of all intensities Tropical Disturbance - distinct area of disturbed weather but usually with no well-defined low-level circulation apparent/ regular advisories not issued/ usually corresponds to Dvorak ratings less than T2.0 Tropical Depression - fairly well-defined low-level circulation/ MSW less than 34 kts/ Dvorak rating usually T2.0 Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5, T3.0, or T3.5 Hurricane - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher The point at which regular advisories are initiated is a little subjective. A system with a Dvorak rating of T1.5 might be upgraded to a tropical depression if it were in a position to affect a populated area and/or if it seemed to be rapidly intensifying and its development potential was considered excellent. 2. JTWC for NORTHWEST PACIFIC Basin Only MSW Averaging Period: 1 minute Tropical Cyclone - generic term for systems of all intensities Tropical Disturbance - distinct area of disturbed weather but usually with no well-defined low-level circulation apparent/ regular advisories not issued/ usually corresponds to Dvorak ratings of T1.0 or less/ MSW generally less than 25 kts Tropical Depression - fairly well-defined low-level circulation/ MSW 25-34 kts/ Dvorak rating usually T1.5 - T2.0 Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5, T3.0, or T3.5 Typhoon - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher Super typhoon - MSW reaching or exceeding 130 kts 3. JTWC for NORTH INDIAN OCEAN and SOUTHERN HEMISPHERE MSW Averaging Period: 1 minute For the North Indian Ocean and all Southern Hemisphere regions, JTWC uses only the generic term "Tropical Cyclone" to refer to systems of all intensities in warning status. Warnings are usually initiated when the system is forecast to produce gale/tropical storm force winds within 48 hours. In many cases winds are already approaching this threshold when the first warning is issued and frequently the initial MSW is set at 35 kts. 4. NORTHWEST PACIFIC Basin - JMA (Japan) MSW Averaging Period: 10 minutes Tropical Cyclone - generic term for systems of all intensities Low-pressure Area - distinct area of disturbed weather but usually with no well-defined low-level circulation apparent/ regular warnings not issued Tropical Depression - fairly well-defined low-level circulation/ MSW less than 34 kts Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating T2.5 or T3.0 Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating T3.5 or T4.0 Typhoon - MSW exceeding 63 kts/ Dvorak rating T4.5 or higher The Japanese Meteorological Agency (JMA) is the World Meteorological Organization's (WMO) official Regional Specialised Meteorological Centre (RSMC) for the Northwest Pacific Basin. While adhering to a 10-min averaging period for MSW, JMA normally equates 34 kts to a Dvorak rating of T2.5; thus, JMA and JTWC agree in principle on the threshold of tropical storm intensity. However, for very intense typhoons, JMA's MSW estimates are usually far below those assigned by JTWC due to a much lower 1-min to 10-min conversion factor for extreme intensities. Other Asian nations' weather services issue tropical cyclone warnings for portions of the Northwest Pacific region, including the Philippines, Hong Kong, China, Vietnam, Taiwan, and Korea. Warnings from these weather services are issued independently of JMA but utilize the same terminology and are usually reasonably close to JMA's positions and intensity estimates. 5. NORTH INDIAN OCEAN Basin - IMD (Indian Meteorological Department) MSW Averaging Period: 1 minute Low-pressure Area - weak, diffuse area of low pressure without a definite surface circulation Depression - well-defined low-level circulation but with MSW generally less than 28 kts/ Dvorak rating of T1.5 Deep Depression - depression with MSW in range of 28-33 kts/ Dvorak rating of T2.0 Cyclonic Storm - tropical cyclone with MSW in range of 34-47 kts/ Dvorak rating T2.5 - T3.0 Severe Cyclonic Storm - tropical cyclone with MSW in range of 48 - 63 kts/ Dvorak rating of T3.5 Very Severe Cyclonic Storm - tropical cyclone with MSW exceeding 63 kts / Dvorak rating T4.0 or higher The Indian Meteorological Department (IMD) is the WMO's RSMC for the North Indian Ocean (Bay of Bengal and Arabian Sea), although the meteorological services of other nations may also issue warnings for portions of the basin. NOTE: Although not formally defined, IMD used the term "superstorm" to describe the very intense Tropical Cyclone 05B in October, 1999, which, based upon JTWC's warnings, peaked at 140 kts. 6. SOUTHWEST INDIAN OCEAN Basin (West of 90E) MSW Averaging Period: 10 minutes Zone of Disturbed Weather - term used to describe weak, ill-defined systems with winds generally less than 25 kts and corresponding to Dvorak ratings of less than T2.0 Tropical Disturbance - MSW usually 25 kts near center/ Dvorak rating usually T2.0 (Beaufort Force 6) / such systems usually classified as tropical depressions by most TCWCs Tropical Depression - MSW in range of 28-33 kts (Beaufort Force 7 - Dvorak T2.5) Moderate Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating of T3.0 - weak T3.5 Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating of strong T3.5 - T4.0 Tropical Cyclone - MSW in range of 64-89 kts/ Dvorak rating of T4.5 - T5.5 Intense Tropical Cyclone - MSW in range of 90-115 kts/ Dvorak rating T6.0 - T6.5 Very Intense Tropical Cyclone - MSW exceeding 115 kts/ Dvorak rating T7.0 - T8.0 The WMO's RSMC for the South Indian region is Meteo France on the French island of La Reunion; however, names are actually assigned by the Sub-regional Tropical Cyclone Advisory Centres on Mauritius (east of 55E) and Madagascar (west of 55E). The La Reunion TCWC employs a conversion factor of 0.88 to convert the 1-minute MSW Dvorak scale to an equivalent 10-minute average scale. (Prior to the 1999-2000 season, the conversion factor used was 0.80.) 7. AUSTRALIAN REGION (longitude 90E eastward to longitude 160E) MSW Averaging Period: 10 minutes Tropical LOW - term is used to describe disturbances ranging from diffuse, ill-defined low-pressure areas all the way to well- organized tropical depressions with MSW up to 33 kts Tropical Cyclone - MSW in range of 34-63 kts/ Dvorak rating ranging from a strong T2.5/weak T3.0 to T4.0 Severe Tropical Cyclone - MSW exceeding 63 kts/ Dvorak T4.5 or higher Warnings in the Australian Region are issued by three separate TCWCs at Brisbane (Queensland), Perth (Western Australia), and Darwin (Northern Territory) with Darwin being the RSMC for the region. In addition to these, a TCWC at Port Moresby, Papua New Guinea (formerly an Australian territory) issues warnings for a small portion of the region near and east of the island of New Guinea. The Papua New Guinea region has an extremely low incidence of tropical cyclone occurrences. The Australian centres avoid use of the term "tropical depression" in public advices primarily to reduce possible confusion with the use of the term "depression" in association with extratropical systems; and also possibly because until recently (early 1990's), in the Southwest Indian Ocean Basin, a "tropical depression" meant any system with winds up to 63 kts (hurricane force). The Australian TCWCs utilize a conversion factor of 0.88 or 0.90 to modify the 1-minute Dvorak scale to an equivalent 10-minute average scale. 8. SOUTH PACIFIC Basin (east of longitude 160E) MSW Averaging Period: 10 minutes Tropical Disturbance - distinct area of disturbed weather but usually with no well-defined low-level circulation apparent/ regular advisories not issued/ usually corresponds to Dvorak ratings less than T2.0 Tropical Depression - fairly well-defined low-level circulation/ MSW less than 34 kts/ Dvorak rating usually T2.0 or weak T2.5 Tropical Cyclone - MSW exceeding 33 kts/ Dvorak rating of strong T2.5/T3.0 or higher The TCWC at Nadi, Fiji, is the RSMC for the South Pacific basin but the meteorological service of New Zealand (Wellington) issues warnings for systems that move (or very rarely form) south of latitude 25S. The Fiji TCWC employs a 1-minute to 10-minute MSW conversion factor of 0.90 when adjusting the Dvorak scale. NOTE: A tropical system can have associated gales and still be classified as a tropical depression if the gales are well-removed from the center. In such cases the gales are usually found in only one or two quadrants. Prior to 2000, the WMO Region V definition of a tropical cyclone required that gales surround the center, but that definition was changed to allow classification as a tropical cyclone if gales were present near the center and likely to persist, even if in only one quadrant. ************************************************************************* ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for April: No tropical cyclones Atlantic Tropical Activity for April ------------------------------------ As would be expected, there were no tropical or subtropical cyclones during April. However, there was a system off the Carolina coastline in mid-April which gave hints of possibly evolving into a subtropical system. I'll describe this system by quoting three e-mails I received pertaining to its development. In the early afternoon of 15 April Matt Crowther wrote: "Looks like we may have a second April subtropical storm in three years (Ana was in 2003). Sat pics show a tight circulation with some convection near the center southeast of North Carolina." Shortly afterward Brian McNoldy replied: "Yeah, I'd agree. I've been watching this all day, and the increased centralized convection is indeed very interesting. Certainly subtropical, and any tropical development would be hard to come by, but still not bad for April. The latest ascending QuikScat pass shows some "clean" (not rain-flagged) winds of 25-35 kts, depending on the quadrant you look at. It's sitting right over the Gulf Stream with SSTs of around 21-22 C, but the outflow temp is cooler than normal too, so keep that in mind." However, early on the morning of 16 April David Roth wrote: "It looked slightly promising yesterday, but all I'm seeing on the morning visible imagery is a textbook occluded cyclone near 31.8N/70.3W with maybe a few showers near the center. Sometimes synoptic-scale LOWs will pick up some convection as they pass over the Gulf Stream. These things happen." ************************************************************************* NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for April: No tropical cyclones ************************************************************************* NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for April: 1 tropical depression ** 1 typhoon ** - classified as a tropical depression by JMA 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 Philippine 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 April --------------------------------------------- Two tropical cyclones formed in the Northwest Pacific basin during the month of April: a typhoon of major intensity and a weak tropical depression. The tropical depression was not recognized by JTWC nor by any of the Asian warning agencies bar JMA and the Central Weather Bureau of Taiwan (CWBT). JMA estimated the MSW at 30 kts, whereas CWBT does not normally make wind estimations for tropical depressions. The system was classified as a tropical depression by JMA only on 18 April as it sat essentially stationary near 7.0N/140.0E, or several hundred miles south-southwest of Guam. A "track" for this system was included in the companion cyclone tracks file prepared by the author, and a graphic displaying the location of this depression may be found at the following link: According to information sent by Huang Chunliang, Yap (WMO 91413, 9.48N/138.08E) picked up 127.0 mm of rainfall during the pre-depression stages of this system between 13/0600 and 14/0600 UTC. The other tropical cyclone of April was Typhoon Sonca (known in the Philippines as Bising). This typhoon followed a rather long trajectory from well east of Palau northwestward, then westward, eventually recurving a few hundred miles east of the central Philippines. Sonca was an impressive typhoon, reaching an intensity of 115 kts (per JTWC). A report on this cyclone, authored by Kevin Boyle, follows. TYPHOON SONCA (TC-03W /TY 0503 / BISING) 20 - 29 April ---------------------------------------------- Sonca: contributed by Vietnam, is a singing bird known for its beautiful twittering sound and which lives in mountainous areas A. Introduction --------------- Typhoon Sonca became the surprise package of April, 2005, in the Western North Pacific, unexpectedly reaching a maximum intensity of 115 kts nearly 600 nm or so east of the Philippines. This storm well illustrates the unpredictability of tropical cyclones. Typhoon Sonca followed a track similar to that of Super Typhoon Sudal last year, but stayed well away from Yap Island. This is the third consecutive year in which April has produced a major typhoon with a MSW > 100 kts. B. Storm Origins ---------------- Two suspect areas were being monitored in JTWC's STWO at 2000 UTC 16 April, one producing thunderstorm activity approximately 170 nm east- southeast of Palau while the second, pre-Sonca, disturbance was located 85 nm south-southwest of Chuuk. As the first was initially considered the more likely to develop into a tropical cyclone, a TCFA was issued at 18/0030 UTC. However, no further development occurred and the TCFA was cancelled at 19/0030 UTC. (This system was the one classified as a tropical depression by JMA on 18 April. See introductory paragraphs above.) The system had dissipated altogether by 19/0600 UTC. Meanwhile, the pre-Sonca LOW had been raised to a 'fair' development potential at 18/2200 UTC. An upper-level analysis depicted a low to moderate wind shear environment with favourable outflow aloft. When multi-spectral satellite imagery revealed convection organizing over a LLCC, a TCFA was released at 20/0530 UTC. This was replaced by the first warning at 20/1200 UTC, placing the centre of the newly formed tropical depression 270 nm east-southeast of Yap. C. Synoptic History ------------------- At 1200 UTC 20 April Tropical Depression 03W was drifting westwards at 7 kts along the southwestern periphery of the mid-level steering ridge situated to the northeast. The storm showed little signs of developing into a tropical storm and remained a very slack, disorganized system during the 21st. Forecasts called for slow strengthening, but as this didn't seem forthcoming, JTWC intended the 22/0000 UTC warning to be the last. Just as this final statement was being released, TD-03W underwent a redevelopment phase and satellite images at this time showed that TD-03W had actually become much better organized. Realizing this, JTWC was forced to reinstate the storm only six hours after the last statement was issued so there was no break in transmission. There was a little intensification on the 22nd but the system remained at tropical depression status. After crossing into PAGASA's AOR at 22/1200 UTC, the name Bising was assigned by that agency for local use. Tropical Depression 03W finally became a named tropical storm at 0000 UTC 23 April after both JTWC and JMA upgraded their respective MSW estimates to 35 kts. The newly-christened Sonca was then centered approximately 375 nm west-northwest of Yap. It was at this point that Tropical Storm Sonca really began to take off. An unexpected rapid strengthening phase ensued, and after a 23/1633 UTC AMSR-E microwave pass depicted a developing eye, Sonca was upgraded to a 75-kt typhoon at 23/1800 UTC while located about 450 nm west-northwest of Yap. After moving rather erratically on a west to northwest track for a couple of days, the storm turned north-northwestward and slowly moved in that direction awhile before veering northwards. Its intensity continued to climb alarmingly, reaching a peak of 115 kts at 24/1800 UTC. At this point, Sonca was located approximately 570 nm east of Manila and was beginning to recurve around the subtropical ridge. (Editor's Note: The peak MSW assigned by JMA was 85 kts with an estimated minimum CP of 940 mb. PAGASA and the CWB of Taiwan also estimated the peak winds at 85 kts (10-min avg), whereas NMCC's was slightly higher at 90 kts.) Even as Typhoon Sonca reached its maximum intensity at 1800 UTC 24 April, increasingly hostile environmental conditions were already distorting the appearance of the system. Its eye soon became cloud- filled at 25/0000 UTC and deep convection began to decrease in the western and southern quadrants. Sonca remained a major typhoon through the 25th until the MSW fell below 100 kts at 26/0600 UTC. The system began to accelerate northeastward into the mid-latitude westerlies and started to take on extratropical characteristics. At 26/1800 UTC Sonca was downgraded to a 55-kt tropical storm only 45 nm west-northwest of Iwo Jima, the island lying within the radius of 34-kt winds. JTWC issued their final warning at this time, but JMA maintained Sonca as a 65-kt typhoon. The latter agency finally classified the system as extra- tropical at 1200 UTC on 27 April with the 45-kt gale center located about 500 nm east-northeast of Iwo Jima and moving rapidly eastward. The final reference to former Typhoon Sonca in JMA's High Seas Bulletins was at 0000 UTC on 29 April and placed the weakening 25-kt LOW about 600 nm north of Wake Island. A graphic depicting the track of Typhoon Sonca may be found at the following link: D. Meteorological Observations ------------------------------ The only meteorological observations available were sent by Huang Chunliang--a couple of rainfall amounts from Chuuk, and these were from the formative stages of Sonca, several days before the depression stage began on 20 April. Only 24-hr amount(s) >= 100 mm listed: CHUUK, ECI (7.45N 151.83E) 116.1 mm [15/18-16/18Z] CHUUK, ECI (7.45N 151.83E) 102.6 mm [16/00-17/00Z] E. Damage and Casualties ------------------------ There were no known damage or casualties associated with Typhoon Sonca. (Report written by Kevin Boyle) ************************************************************************* NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for April: No tropical cyclones ************************************************************************* SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E Activity for April: 1 severe tropical storm 1 very intense tropical cyclone ** ** - system formed east of 90E in Australian Region 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 Tropical Cyclone Advisory Centres in Mauritius and Madagascar with longitude 55E being the demarcation line between their respective areas of naming 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 April -------------------------------------------------- Two tropical systems stirred Southwest Indian Ocean waters during the month of April. Severe Tropical Storm Isang formed slowly in the eastern part of the region early in the month and followed a poleward trajectory through the central Indian Ocean, passing several hundred miles east of Rodrigues Island. Isang remained weak for most of its life, intensifying into a severe tropical storm only after reaching subtropical latitudes and encountering the westerlies. The system may have briefly reached tropical cyclone (i.e., hurricane) intensity shortly before becoming extratropical. The other system was a visitor, having formed in the Australian Region, but was one of the most intense tropical cyclones in the South- west Indian Ocean during the 2004-2005 season. Christened Adeline by BoM Perth on 3 April near the Cocos Islands, the system moved westward, reaching hurricane intensity on the 4th before crossing 90E into MFR's region of warning responsibility on the 5th. The storm then became Tropical Cyclone Juliet and reached a peak intensity of 120 kts as it recurved less than 200 nm east of Rodrigues Island. A report on Severe Tropical Storm Isang follows. A report on Tropical Cyclone Adeline-Juliet can be found in the next section of this summary covering the Northwest Australia/Southeast Indian Ocean region. SEVERE TROPICAL STORM ISANG (MFR-17 / TC-25S) 29 March - 7 April ----------------------------------------------- Isang: contributed by Botswana A. Storm Origins ---------------- Severe Tropical Storm Isang was a system which spent the first half of its life as a rather weak tropical disturbance. Furthermore, after it had been named, Isang remained a minimal tropical storm until it had moved into the subtropics and was approaching the westerlies. At the last possible moment the system strengthened suddenly into a severe tropical storm, then quickly became extratropical. An area of convection formed and persisted approximately 800 nm east- southeast of Diego Garcia on 29 March. Deep convection was beginning to consolidate around a LLCC, and enhanced water vapor imagery showed that outflow was improving in the equatorward direction. An upper-level analysis indicated that the LLCC was located in an environment of moderate to high vertical shear and increasing 850-mb vorticity. MFR initiated bulletins on the developing system at 1800 UTC on 29 March, numbering it as Tropical Disturbance 17. The broad center was then located roughly 750 nm east-southeast of Diego Garcia. JTWC issued a TCFA at 0200 UTC on the 30th after satellite imagery revealed an increase in deep convection and the formation of a possible CDO. However, only seven hours later the TCFA was cancelled after the LLCC was shown to have become fully-exposed with the deep convection located approximately 150 nm west of the LLCC. MFR maintained the disturbance as a 25-kt system for the next few days as it moved slowly and erratically on a generally west-southwesterly course. The organization of the system apparently fluctuated during this time as JTWC went through a couple of cycles of upgrading the development potential and then downgrading it to poor. The circulation associated with Tropical Disturbance 17 was very large--the MFR warning issued at 0600 UTC on 1 April noted that squally weather existed up to 750 nm from the center in the western semi-circle and up to 300 nm on the eastern side. Things began to look more hopeful for the system on 3 April. In an interim STWO issued at 0700 UTC JTWC upgraded the development potential to fair as deep convection began to consolidate over the LLCC. MFR upgraded the system to a 30-kt tropical depression at 03/0600 UTC, and at 1200 UTC Tropical Storm Isang was christened. The new tropical storm was then centered about 500 nm east-northeast of Rodrigues Island. B. Synoptic History ------------------- After being upgraded to tropical storm status, Isang's track began to trend more to the southwest as it moved around the western periphery of the subtropical ridge to the southeast. The system remained at minimal tropical storm intensity through 4 April, due in part to the inhibiting influence of being located in an environment of drier air. Tropical Storm Isang continued to track southwestward, reaching its point of recurvature at around 1200 UTC on 5 April when it was located about 150 nm east-southeast of Rodrigues Island. As the storm turned toward the south, the deep convection coupled vertically with the LLCC, leading to an increase in the intensity. Isang reached its peak intensity of 60 kts at 1200 UTC on 6 April while located near 26.3S/67.0E, or about 465 nm southeast of Rodrigues. The storm by this time was moving off toward the south-southeast at 17 kts into an environment of increasing vertical shear and cold, dry air. Only twelve hours after reaching its peak intensity, Isang was declared extratropical. The final warning issued on Isang by MFR as the extratropical storm exited the agency's AOR placed the center about 800 nm southeast of Rodrigues at 0600 UTC on 7 April. The minimum CP estimated by MFR was 975 hPa. JTWC's estimated peak 1-min avg MSW was 55 kts on 6 April. In an e-mail Karl Hoarau noted that MFR later stated that Isang had briefly reached the tropical cyclone stage around 0600 UTC on the 6th with the MSW (10-min avg) estimated at 65 kts, so it's possible Isang will be upgraded posthumously. A TRMM 85-GHz image taken at 06/0620 UTC shows a fairly well-defined eye feature. It's very interesting that Isang's spurt of intensification occurred at such a high latitude with the cyclone located in a seemingly rather hostile environment. A graphic displaying the track of Severe Tropical Storm Isang may be found at the following link: C. Damage and Casualties ------------------------ There are no reports of any damage or casualties resulting from Severe Tropical Storm Isang. (Report written by Gary Padgett) ************************************************************************* NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E Activity for April: 1 severe tropical cyclone Sources of Information ---------------------- The primary sources of tracking and intensity information for Northwest Australia/Southeast Indian Ocean tropical cyclones are the warnings and advices issued by the Tropical Cyclone Warning Centres at Perth, Western Australia, and Darwin, Northern Territory. 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 the Australian centres' coor- dinates 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. Northwest Australia/Southeast Indian Ocean Tropical Activity for April ------------------------------------------ One tropical cyclone sprang to life in the Southeast Indian Ocean east of 90E during April. Named Adeline by the Perth TCWC near the Cocos Islands on 3 April, Adeline reached hurricane intensity the next day as it chugged westward across the Indian Ocean. After crossing 90E on the 5th, Adeline was renamed Juliet by Mauritius and eventually became a very intense 120-kt cyclone as it recurved a couple hundred miles east of Rodrigues Island. A report on Severe Tropical Cyclone Adeline-Juliet follows. VERY INTENSE TROPICAL CYCLONE ADELINE-JULIET (MFR-18 / TC-26S) 1 - 14 April ---------------------------------------------------------------- Adeline: assigned by BoM Perth Juliet: contributed by Zimbabwe A. Storm Origins ---------------- The daily STWO issued by BoM Perth on 1 April mentioned a tropical LOW which had formed roughly 385 nm east-northeast of the Cocos Islands. The LOW was basically stationary and was given a high potential for development into a tropical cyclone over the next couple of days. On the same day JTWC issued an interim STWO for the same disturbance, noting that convection was becoming increasingly organized over a possible LLCC and that an upper-level analysis indicated favorable divergence aloft. However, JTWC considered the chances for development over the next 24 hours to be poor. Due to the potential threat posed to the Cocos Islands, BoM Perth began issuing tropical cyclone advices for the islands, and high seas gale warnings were begun at 1600 UTC, indicating that gales could develop within the next 18 to 24 hours. B. Synoptic History ------------------- Initially moving westward, the LOW turned to a southwesterly track on the 3rd in the general direction of the Cocos Islands. The system continued to exhibit increasing deep convection and improving outflow. At 03/0700 UTC JTWC issued an interim STWO upgrading the potential for development to fair, and at 1000 UTC BoM Perth upgraded the LOW to Tropical Cyclone Adeline, located only about 25 nm east of the Cocos Islands. As Adeline passed just to the south of the Cocos, its track shifted to the west. The system continued to steadily intensify, with the MSW reaching 55 kts by 1000 UTC on 4 April. (JTWC issued their first warning on TC-26S at 04/1800 UTC, estimating the 1-min avg MSW at only 35 kts, but issued an amended warning a few hours later upping the winds to 55 kts.) At this stage Adeline was undergoing a spurt of rapid intensification which carried the winds to hurricane force by 2300 UTC, at which time the cyclone was centered approximately 300 nm west-southwest of the Cocos Islands. Severe Tropical Cyclone Adeline continued to intensify as it headed for longitude 90E--the boundary between Perth's AOR and that of Mauritius and Meteo France La Reunion--with winds reaching 75 kts by 1000 UTC on 5 April. The 05/1000 UTC warning was the last issued by BoM Perth. MFR issued their first warning on the cyclone at 1200 UTC as it was about to cross the line of demarcation. Following the long-standing custom in that part of the world, the Meteorological Service of Mauritius renamed the storm Juliet with MFR referring to it as Tropical Cyclone Juliet/ex-Adeline for a couple of days. Shortly after crossing into the Southwest Indian Ocean basin proper, Adeline-Juliet underwent another round of rapid intensification with winds reaching 105 kts at 0600 UTC on 6 April. The intense cyclone's center was then located approximately 575 nm west of the Cocos Islands and moving westward at 8 kts. After remaining at 105 kts for 24 hours, Juliet began to weaken a bit with the MSW dropping to 80 kts by 1800 UTC on 7 August. The cyclone had also turned to more of a west-southwesterly track, although it moved due westward for an 18-hour period early on the 8th. Tropical Cyclone Juliet began to re-intensify at 08/1800 UTC and reached its peak intensity of 120 kts at 0000 UTC on 10 April when located about 175 nm east-northeast of Rodrigues Island. The estimated CP was a very low 905 hPa. Hurricane-force winds extended outward up to 60 nm in the southern quadrants and gales covered an area over 350 nm in diameter. (This wind radii information taken from MFR's warnings.) The west-southwesterly track of the previous few days began to trend more southwesterly as the very intense cyclone approached the small island. The closest approach to Rodrigues occurred around 10/0600 UTC when Juliet's center lay about 115 nm to the east-southeast. After passing Rodrigues Juliet's track became increasingly southerly and the cyclone began to steadily weaken as it entered an unfavorable environment of drier air, increasing vertical shear and cooler SSTs. The cyclone's point of recurvature was near 24.2S/63.4E at 1200 UTC on 11 April. Winds were then estimated at 75 kts, but twelve hours later MFR downgraded Juliet to a 60-kt tropical storm. An 11/1642 UTC SSM/I image showed that the deep convection had become decoupled south- east of the LLCC with cold, dry air entrained into the western semi- circle. At 12/0600 UTC MFR classified the cyclone as an extratropical storm, and at the same time JTWC issued their final warning. Ex-Juliet by this time was moving southeasterly, and subsequently followed a track slightly south of due east. The extratropical gale continued to weaken and MFR issued the final bulletin at 14/1200 UTC with the 25-kt LOW located around 1000 nm southeast of Rodrigues Island. At Adeline-Juliet's first peak in intensity, JTWC estimated the peak 1-min avg MSW at 115 kts, which agrees well with MFR's 105 kts (10-min avg). At the second and maximum peak at 10/0000 UTC, MFR estimated the peak 10-min avg MSW at 120 kts. JTWC did not issue a warning at this hour, but the previous one at 09/1800 UTC pegged the MSW at 130 kts (1-min avg)--MFR's estimate at that time was 115 kts which is equivalent to 130 kts 1-min avg. A graphic displaying the track of Tropical Cyclone Adeline-Juliet may be found at the following link: C. Damage and Casualties ------------------------ No fatalities or damage are known to have resulted from Tropical Cyclone Adeline-Juliet. (Report written by Gary Padgett) ************************************************************************* NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E Activity for April: 1 possible tropical cyclone Sources of Information ---------------------- The primary sources of tracking and intensity information for Northeast Australia/Coral Sea tropical cyclones are the warnings and advices issued by the Tropical Cyclone Warning Centres at Brisbane, Queensland, and Darwin, Northern Territory, and on very infrequent occasions, by the centre at Port Moresby, Papua New Guinea. 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 the Australian centres' coor- dinates 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. Northeast Australia/Coral Sea Tropical Activity for April ----------------------------- No tropical cyclones formed in BoM Brisbane's AOR during April, but there was an interesting system near Papua New Guinea which very possibly was a short-lived midget tropical cyclone. This system formed within Port Moresby's area of warning responsibility and brought strong winds well above gale force to Port Moresby and surrounding areas. The LOW was not named as a tropical cyclone, but the Brisbane TCWC issued gale warnings for the system, and the evidence strongly suggests that it was a bona fide tropical cyclone. A report on this system, authored by Simon Clarke, follows. About a week after the above-mentioned system there was another LOW in the Solomon Islands region which displayed some deep convection near the center and could have been classified as a tropical depression. However, the system was located in a region of moderate shear and never became all that well-organized. BoM Brisbane mentioned this system in their STWOs on 23 and 24 April. PAPUA NEW GUINEA STORM 14-15 April ------------------------------------------ A. Synoptic History ------------------- A tropical LOW first became apparent in the far northern Arafura Sea on 12 April 2005. This LOW moved eastward close to the southern coastline of Papua New Guinea from 13 to 16 April and may have developed into a rare midget cyclone in the Torres Strait. At 14/2230 UTC a gale warning was issued by BoM Queensland for a developing LOW of 995 hPa near 9.3S/144.0E, or approximately 140 nm northeast of Cape York, Queensland, and 160 nm west of Port Moresby, Papua New Guinea. The Kumul Oil Search Marine Terminal at 8.1S/144.6E recorded gusts to 55 knots as the system passed to the south. The LOW moved eastward at approximately 10 kts and deepened to 993 hPa as the system developed deep convective banding over its western quadrants. At 15/0308 UTC the LOW was 90 nm west of Port Moresby and producing very rough seas and clockwise gales of 35-40 kts (and possibly to 50 kts) within 60 nm of the centre. However, as the LOW approached and interacted with the southeastern landmass of Papua New Guinea and moved into a region of increasing upper shear, it weakened and the final gale warning was issued at 15/1854 UTC with the LOW near 10.5S/148.5S, or approximately 120 nm east-southeast of Port Moresby. The LOW later succumbed to strong northeasterly wind shear. Jeff Callaghan advises that the Cairns, Queensland, BoM office received calls from the public at Port Moresby since gales were being experienced there. The Port Moresby office released a balloon at the Port Moresby airport at 0000 UTC 15 April and the winds at 925 hPa were 340/49 knots and at 894 hPa were 337/54 knots, which is consistent with gales or worse in the Port Moresby area. A QuikScat pass soon afterward depicted gales surrounding the LOW. A graphic displaying the track of this system may be found at the following link: B. Storm Effects ---------------- The following extract is taken from "The National" (15 April 2005): "A STORM accompanied by strong winds wrecked havoc in Port Moresby on Friday, causing major disruptions to electricity, communication and airline flights. "The heavy rain and winds brought down trees which blocked roads, knocked down at least two power lines, and caused the Burns Peak Repeater Site Tower to collapse, which disrupted communications. "Four Air Niugini flights out of Port Moresby were also cancelled due to bad visibility. According to an officer at the airlines customer service, flights to Goroka, Lae, Rabaul and Mt. Hagen were cancelled due to the bad weather and had to be rescheduled to the next day. PNG Power issued a statement warning the public to stay away from fallen power lines while the linesmen were busy all weekend trying to attend to the fallen power lines. Telikom reported the collapse of its transmission tower located at Burns Peak at about 11 AM which affected mobile coverage, radio, and major business operations of Curtain Brothers, Napa Oil Refinery and Atlas Steel and other essential services. "In Port Moresby, the city was thrown into blackout as electricity supply was cut off by fallen trees along various parts of the city while the busy Port Moresby traffic was brought to crawling pace from heavy flooding of the roads. In downtown Port Moresby, strong winds caused a tree and a power pylon to collapse over a vehicle while at Koki Point several passengers escaped with minor injuries when a power pylon collapsed over a vehicle. "A St. John Ambulance officer confirmed the incident but reported no major harm to the passengers. The officer also reported that two pedestrians were allegedly hit by a vehicle during the poor visibility late Friday at Big Rooster in Boroko. "As of yesterday afternoon, several residents were reportedly without electricity supply after the disruptions on Friday. PNG Power issued a statement saying workmen were still attending to fallen lines. The general public in Port Moresby and surrounding areas are advised to treat all fallen lines as still alive and report to PNG Power 24-hour services, said Grant Hoffmeister, the acting Chief Executive Officer of PNG Power. "Telikoms acting managing director Noel Mobiha also advised that restoration of services may be delayed but every effort will be taken to restore the services. In Daru, a duty policeman said two people were swept out to the mainland by the strong winds but were recovered a day later on the mainland." (Report written by Simon Clarke with significant contributions by Jeff Callaghan) ************************************************************************* SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E Activity for April: 3 tropical depressions 1 tropical cyclone of gale intensity Sources of Information ---------------------- The primary sources of tracking and intensity information for South Pacific tropical cyclones are the warnings and advisories issued by the Tropical Cyclone Warning Centres at Nadi, Fiji (for waters north of latitude 25S), and Wellington, New Zealand (for waters south of latitude 25S). 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 the Southern Hemisphere centres' 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. South Pacific Tropical Activity for April ----------------------------------------- Tropical activity returned to the South Pacific basin in April following a month-long quiescence. No less than five systems were numbered by RSMC Nadi, but only one was upgraded to tropical cyclone status, and this was only for a brief period. Tropical Depression 15F was upgraded to Tropical Cyclone Sheila on 22 April, but was maintained as a tropical cyclone for only 12 hours. Another system, Tropical Disturbance 16F, was apparently absorbed by Sheila during its brief tenure as a named tropical cyclone. To the author's knowledge, TD-16F was never classified as a tropical depression. Three other systems were classified by Fiji as tropical depressions: 14F, 17F and 18F. Tropical Depression 14F was a very persistent system which was mentioned in Nadi's Tropical Disturbance Summaries from the 14th of April until the first of May. The system was relocated several times, and it's possible that the number was applied to more than one weak LLCC embedded in the monsoon trough. TD-14F began well to the northwest of Vanuatu, cruised around the islands of Vanuatu, then took a Fiji vacation, and eventually wound up meandering around over the waters between Fiji and Samoa. Tropical Depression 17F occurred from 26 April to 1 May and spent its lifetime basically meandering over waters north and north-northeast of Vanuatu. The final and shortest-lived of the series, Tropical Depres- sion 18F, formed on 29 April north of Fiji and moved southward, thence jogging eastward, dissipating on 1 May just east of the Fijian islands. Interestingly, all three depressions met their demise on 1 May and were last mentioned in Nadi's 1800 UTC Tropical Disturbance Summary on that date. Graphics depicting the tracks of these tropical depressions may be found at the following links: TROPICAL CYCLONE SHEILA (TD-15F) 20 - 23 April ------------------------------------------- Tropical Cyclone Sheila was the ninth tropical cyclone to form in the Southwest Pacific during the 2004/2005 season and the first in a seven week gap since the previous cyclone in early March. The initial LOW that developed into Sheila (TD-15F) was one in a series of low-pressure centres (TD-14F, TD-16F and TD-17F) that were part of a persistent monsoonal trough that extended from north of the Solomon Islands to Fiji from as early as 16 April. The series of depressions were located over SSTs of about 28-29 C. However, strong upper-level northwesterly shear of 25-30 kts at the 250-hPa level inhibited development of these systems until 21 April when TD-15's LLCC became covered with convection close to its centre. Strong surface westerly winds were established on TD-15's northern side, while a high- pressure system over New Zealand provided a good southeasterly surge to the south, providing the impetus for further development. TD-15 moved to the southeast at 20 kts, running down the axis of the South Pacific Convergence Zone as it was steered by northwesterlies at middle levels. In doing so the depression moved along with the upper-level flow and consolidated sufficiently to attain cyclone status, being named Sheila at 22/0600 UTC near 18.4S/168.8W, or approximately 65 nm northeast of Niue. Sheila passed to the near north of TD-16 and wrapped this depression into its overall circulation. Sheila reached a peak intensity at 22/1200 UTC (CP of 990 hPa, maximum 10-min avg winds of 40 kts) near 19.3S/166.4W. However, Sheila continued to be a sheared cyclone with the LLCC soon becoming exposed on the western edge of the CDO as winds at 250-hPa increased to 45 kts. Cyclone status was lost at 22/1800 UTC near 20.2S/165.4W, or approximately 240 nm east-southeast of Niue, only 12 hours after being named. The remnant extratropical LOW merged with a frontal system to the south soon after. A graphic displaying the track of Tropical Cyclone Sheila may be found at the following link: According to information sent by Huang Chunliang, during the formative stages Nausori, Fiji (WMO 91683, 18.05S/178.57E) received 120.4 mm of rainfall during the 24 hours between 20/0000 and 21/0000 UTC. Sheila passed close to the island of Niue where peak 10-min avg winds of 33 kts were reported. However, it is not fully clear whether or not these winds were associated with TD-16F rather than Sheila. There were no reports of incidents associated with Sheila. (Report written by Simon Clarke) ************************************************************************* 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 August, 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, Chris Landsea, and John Diebolt): 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 Annual Tropical Cyclone Report (ATCR) for 2004 (2003-2004 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 2004 Atlantic and Eastern North Pacific tropical cyclones; also, storm reports for all the 2004 Atlantic and Eastern North Pacific cyclones are now available, as well as track charts and reports on storms from earlier years. The URL is: 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: garyp@alaweb.com Phone: 334-222-5327 Kevin Boyle (Eastern Atlantic, Western Northwest Pacific, South China Sea) E-mail: newchapelobservatory@btinternet.com John Wallace (Assistance with Eastern North Pacific) E-mail: dosidicus@aol.com Huang Chunliang (Assistance with Western Northwest Pacific, South China Sea) E-mail: huangchunliang@hotmail.com Simon Clarke (Northeast Australia/Coral Sea, South Pacific) E-mail: saclarke@iprimus.com.au ************************************************************************* ************************************************************************* Posted: 06.02.05 / Typhoon2000.ph, Typhoon2000.com