GARY PADGETT'S MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY DECEMBER, 2000 (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.) *********************************************************************** DECEMBER HIGHLIGHTS --> Intense tropical cyclone strikes Northwestern Australia --> Intense typhoon rapidly intensifies, then rapidly weakens --> Cyclone of hurricane intensity strikes Sri Lanka *********************************************************************** ***** Feature of the Month for December ***** ATLANTIC SUBTROPICAL SYSTEMS OF 2000 (Part 3) ------------------------------------ This is Part 3 of a three-part feature detailing cyclonic systems of 2000 in the Atlantic which were either subtropical storms or depressions or else exhibited some of the features of subtropical cyclones. The information presented below is taken from material supplied by David Roth of HPC. Please refer to Part 1 in the October summary for more background information and some explanations and caveats. I am repeating here the table of subtropical/hybrid systems which David provided. (Numbers in parentheses following the storm designation refer to explanatory notes below.) I. Subtropical Depression May 19-25 II. Alberto (1) August 14-16 III. Subtropical Storm (2) August 28-30 IV. Subtropical Depression September 10-11 V. Florence (3) September 10-12 VI. Gordon (1) September 17-18 VII. Helene (1) September 24-25 VIII. Subtropical Storm (2) September 30-October 3 IX. Leslie (3) October 4-8 X. Michael (3) October 14-17 XI. Subtropical Storm (4) October 25-28 (1) The official NHC "best tracks" do not treat any portion of Alberto, Gordon, or Helene as subtropical. In general, once a tropical cyclone has been named, NHC treats it as a tropical system through- out the remainder of its life--both operationally and in post- analysis--even if at some point it exhibited some subtropical features. (2) According to Jack Beven, these two systems possibly could qualify as subtropical storms pending a careful analysis of all the available data. For the time being they should be regarded as possible subtropical storms. (3) Subtropical portions of the tracks of Florence, Leslie, and Michael are designated in the "best tracks" for these cyclones. The dates of their subtropical phases, however, might not necessarily agree with those David has assigned above. (4) This storm has already been officially recognized as a subtropical storm by TPC/NHC. Part 1 (October summary), in addition to some introductory material, contained David's discussions of two of the systems occurring in October (Nrs VIII and XI in the table above). The November summary (Part 2) featured some of the named tropical cyclones which exhibited hybrid or subtropical characteristics for part of their lives. This final installment discusses the remaining subtropical systems which David identified: subtropical depressions in May and September (Nrs I and IV) and a possible subtropical storm in August (Nr III). I. Subtropical Depression, May 19-25. Satellite images and surface analyses revealed a frontal wave developing south-southeast of Bermuda on the 17th. Over the next couple of days, a 500-mb LOW cut off in its vicinity, leading to occlusion. By the 19th the system became devoid of fronts and had entered the subtropical stage. Its main nontropical characteristic was a dry slot that encircled the center on the 19th. Development of the cyclone occurred over 24 C waters and convection was present well east and northeast of the center which slowly warmed its core. The system reached its peak just as it entered the subtropical stage, and weakened steadily thereafter as upper-level winds out of the west began shearing the cyclone to the east, exposing a low-level swirl on the 20th. The circulation became elongated on the 23rd with multiple circulation centers before becoming absorbed into a warm front on the 24th and 25th. No gale-force winds were reported on the surface maps with this cyclone, though gales were possible. The highest winds reported were 30 kts. (Some information on this system was reported in the May global summary.) III. Possible Subtropical Storm, August 28-30. Hurricane Debby had dissipated in the northwestern Caribbean on the 24th. Some of its weather spread northward as a cold front was invading northern Florida. A tropical disturbance formed over 28 C waters in the inverted trough ahead of the cold front on the 28th near the Bahamas as a closed 500-mb LOW (with temps of -12 C at that level) was entering the scene from the mid-Atlantic. The 29th featured a complex situation, as a mesoscale convective complex formed to the east of the northward-moving LOW and accelerated northeastward in an area (confirmed by ship reports) of uniform southerly winds. The frontal boundary in the LOW's vicinity had weakened, and thunderstorms were constricted to its east side as winds aloft were westerly and its central pressure was falling. On the 30th a tight circulation formed off North Carolina with a small, concentrated area of thunderstorms as the LOW was swung around the 500-mb LOW. Gale-force winds were reported by two buoys near the coast, but existed only briefly as the system soon moved inland near Wilmington and subsequently weakened. Operationally this LOW was treated as a nontropical gale, but some local forecast discussions addressed the cyclone as subtropical with one or two believing it to be fully tropical. However, a large dry slot was present to the south- west and south of the center--a definite nontropical characteristic. As the LOW moved inland, it dumped an average of 50-75 mm of rain near and to the right of its track from North Carolina west-southwestward into northern Georgia. The closed low-level circulation dissipated near Atlanta on the evening of the 30th. More information on this system can be found in the global summary for August. Jack Beven of TPC/NHC has indicated that all available data for this cyclone will be carefully examined to see if it qualifies for inclusion in the Best Track database as a subtropical storm. IV. Subtropical Depression, September 10-11. A frontal wave formed southwest of Bermuda on the 9th. The system quickly occluded and shed its frontal boundaries by the 10th while sitting over 26 C waters. It moved eastward as a cold front approached on the 11th, moving south of the Azores. By the 12th the circulation had been absorbed into this front. The highest winds seen were 20 kts via ship reports and land observations, which were sparse. *********************************************************************** ACTIVITY BY BASINS ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico Activity for December: No tropical cyclones *********************************************************************** NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180 Activity for December: No tropical cyclones *********************************************************************** NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180 Activity for December: 1 tropical depression ** 1 typhoon ++ ** - treated as a tropical depression by PAGASA only ++ - system did not reach typhoon intensity until early January, 2001 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 December ------------------------------------------------ As the month of December opened Tropical Storm Rumbia/Toyang was in the process of crossing the southern Philippines. The storm moved westward into the South China Sea, weakened into a tropical depression, later re-intensified briefly into a minimal tropical storm, and finally dissipated near the southern tip of Vietnam. (Please see the November summary for the full report on Rumbia.) A tropical disturbance developed early in the month east of the Philippines and moved westward into the central portions of the archipelago. JTWC never issued any warnings on this system, although it was given a development potential of Fair on a couple of occasions. PAGASA, however, upgraded the system to a tropical depression on 6 December and assigned the name Ulpiang. Tropical Depression Ulpiang remained broad and disorganized but moved through the central Philippines where it brought very heavy rains which led to extensive flooding and loss of life. Based upon PAGASA's track (forwarded to me by Michael V. Padua), Ulpiang's center crossed over the island of Samar, then through the cluster of smaller islands lying to the west of Samar, eventually reaching the vicinity of Mindoro where it weakened to the point that warnings were discontinued. According to Mike Padua, Naga City (his hometown) was flooded by the rains of Ulpiang. Two stations south of Naga City (Lake Bato and Ligao) each recorded 200 mm of rain in the 24-hour period ending at 6:00 am on the 8th. Ocampo, located a short distance southeast of the city, recorded 160 mm in the same period. While Naga City itself recorded only 68 mm, the city was flooded because it lies below sea level and is in the catchment basin of the Bicol River (including its tributaries). At least 20 fatalities were caused by the depression's rains, the majority occurring on the island of Panay, although three persons were killed in a landslide in the Bicol region of southeastern Luzon. More than 50,000 persons were displaced when floods inundated 16 towns and Roxas City (on Panay). Many roads and bridges were damaged and hundreds of hectares of rice fields and other farms were flooded. The final tropical storm of 2000 also became the first typhoon of 2001. Tropical Storm Soulik formed deep in the tropics east of the southern Philippines late in the month, moved generally northward, and as the month (and year) closed was headed northeastward out into the Philippine Sea and weakening. However, on 3 January the storm intensified with extreme rapidity into an intense 115-kt midget typhoon which, after maintaining that intensity for only twelve hours, encountered strong vertical shear and dry air and dissipated almost as quickly as it had intensified. Typhoon Soulik (TC-34W / TY 0023 / Welpring) 28 December - 5 January, 2001 --------------------------------------------- Soulik: contributed by the Federated States of Micronesia, is a traditional Pohnpei Chief's title The final NWP tropical cyclone of 2000 was at the same time the first typhoon of 2001. After forming deep in the tropics east of Mindanao and peaking at 55 kts on 31 December, Tropical Storm Soulik had begun to weaken by 2 January and was forecast to continue to dissipate. However, the capricious storm had other ideas. The storm's intensity (based on JTWC's 1-min MSW estimates) literally exploded on 3 January, increasing from 45 kts to 115 kts in just 18 hours! And then after only 12 hours, the storm weakened from a 115-kt typhoon to a 25-kt dissipating depression in only 30 hours. Episodes of such rapid intensification are rare in tropical cyclones, but none- theless do occur and emphasize why even weaker storms which may appear to be weakening should not be written off too soon. Rapid dissipation of cyclones such as that exhibited by Soulik is also not common. Soulik's demise was reminiscent of the decay of Typhoon Jack in December, 1989. Jack weakened from 120 kts to 30 kts in a 30-hour period. An area of convection developed on 27 December about midway between Palau and Mindanao. A broad LLCC was present with the most persistent convection to the north. Vertical wind shear was weak and outflow was fair. JTWC upgraded the development potential to Fair at 28/0600 UTC and issued a Formation Alert at 28/1930 UTC. Organization had improved with increased convective banding noted. A 28/1712 UTC TRMM pass depicted a fully-exposed LLCC located about 200 nm east of the island of Mindanao with the deep convection sheared to the north. The trend toward further development continued and JTWC initiated warnings on TD-34W at 29/0000 UTC. PAGASA also upgraded the disturbance to a tropical depression at the same time and named it Welpring. A ship report at 29/0000 UTC about 60 nm west of the center indicated a northwesterly wind of 22 kts. The initial warning indicated that the depression was quasi-stationary, but the next warning at 0600 UTC relocated the center about 100 nm to the north of the previous warning position based on visible satellite imagery and a 29/0143 UTC ERS-2 scatterometer pass. TD-34W/Welpring was moving slowly northward and was forecast to continue this motion due to the steering influence of a low- to mid-level ridge east of the system. PAGASA was already estimating the 10-min avg MSW at 30 kts, but JTWC increased their MSW estimate to 30 kts at 1200 UTC based on a synoptic ship report of 28 kts. At 1800 UTC JTWC relocated the center of the depression once more, this time to the west as the convection was beginning to consolidate over the LLCC. TD-34/Welpring had also begun to track to the northwest as it intensified. A synoptic ship report of 35 kts around 30/0000 UTC led to the system's being upgraded to a tropical storm by JTWC, PAGASA and JMA, with JMA assigning the name Soulik. Soulik's center at the time was located approximately 200 nm east of Surigao on the northern tip of Mindanao, moving northwestward at 9 kts. This northwestward motion was forecast to come to a halt and a northeasterly track commence as a mid-latitude trough approached and weakened the ridge which was steering the storm. This forecast soon came to pass. At 30/1200 UTC Tropical Storm Soulik reached the westernmost point of its trajectory about 135 nm northeast of Surigao; by 1800 UTC the storm was moving northeastward. Soulik's MSW had reached 55 kts (per JTWC) by 0000 UTC on 31 December and the cyclone maintained this intensity for three days before weakening some. (JMA's estimated peak 10-min avg wind was 50 kts for the same 72-hour period.) During this time Soulik moved generally on a northeastward to east-northeastward course. Interestingly, at 1200 UTC on the 31st, JTWC received satellite current intensity estimates of 45, 55, and 77 kts. The JTWC warning at 0000 UTC on 1 January noted that the storm was located at the tail end of a long front extending southeast across the Philippine Sea. The convection had become elongated, although the LLCC still appeared to be organized. At 1800 UTC JTWC relocated Soulik to a position 60 nm southeast of the previous warning position or about 625 nm west-northwest of Guam. A 01/1534 UTC TRMM pass depicted a partially-exposed LLCC southeast of the isolated deep convection. A 700-mb HIGH east of the Mariana Islands with an associated ridge extending southwestward over Mindanao was expected to continue steering Soulik east-northeastward. The storm continued to show signs of weakening on 2 January. Areal extent of deep convection decreased and animated water vapor imagery revealed transverse banding just north of the system, indicative of strong westerlies aloft. JTWC and JMA both decreased their respective MSW estimates to 45 kts at 02/0600 UTC. Satellite imagery around 1200 UTC showed that the LLCC was embedded about 60 nm under the cirrus cloud shield, but a 02/0906 UTC SSM/I pass depicted weakening banding and organization with a partially-exposed LLCC south of the deepest convection. Soulik was forecast to continue weakening, but the storm maintained its intensity throughout the day. The storm's forward motion had slowed, thereby allowing deep convection to consolidate once more around the center. JTWC increased the MSW to 55 kts at 0000 UTC on the 3rd while JMA upped their maximum 10-min avg wind estimate to 50 kts. Soulik was at that time located about 570 nm south-southwest of Iwo Jima and moving northward at 5 kts. Shortly after 03/0000 UTC, however, the fireworks really started! Based upon satellite intensity estimates ranging from 65 to 115 kts, JTWC upgraded Soulik to a 105-kt typhoon at 0600 UTC. The storm had intensified very rapidly during the previous six hours and sported a 7-nm round eye. A 200-mb analysis revealed an upper-level HIGH developing over the system and animated water vapor imagery depicted good outflow aloft. Typhoon Soulik reached its peak estimated intensity of 115 kts (per JTWC) at 1200 UTC on 3 January when it was located about 500 nm southwest of Iwo Jima. Satellite intensity estimates were ranging from 90 to 127 kts. At its peak Soulik was a small, symmetric system with intense central convection. 50-kt winds extended outward from the center only 25 nm to the southeast and gales covered an area only 140 nm in diameter. JMA's peak 10-min avg wind estimate for Soulik was 80 kts at 03/1800 UTC. Even as the cyclone reached its peak, cooler, drier air was impinging on its northwestern quadrant and convection was beginning to elongate to the northeast. As noted earlier, the demise of Typhoon Soulik was not much less rapid than its intensification with the storm weakening (per JTWC's MSW) from 115 kts to 25 kts in 30 hours. Strong vertical shear and colder, drier air that was entrained into the system were the primary culprits responsible for the quick extinction of Soulik. The MSW had fallen to 65 kts--minimal typhoon intensity--by 1200 UTC on 4 January when it was located about 440 nm southwest of Iwo Jima, and 12 hours later Soulik was a dissipating depression. The 1200 UTC warning noted that the weakening storm's motion had changed to the southeast, but the final JTWC warning at 05/0000 UTC relocated the center about 170 nm to the southwest of the previous analysis position (to a point about 700 nm east of Catanduanes Island in the Philippines). This relocation was based upon the first visible satellite pictures of the day. The intensity was lowered from 50 kts to 25 kts with animated satellite imagery indicating a fully-exposed LLCC which was beginning to break down on the southern side. (The JMV file for Typhoon Soulik, which may be considered a first cut at a Best Track, begins to move the storm back to the south-southwest at 04/1200 UTC and also reduces the MSW to 55 kts at 1200 UTC and to 40 kts at 1800 UTC.) In its earlier stages Tropical Storm Soulik/Welpring approached to within about 100 nm of northern Mindanao in the Philippines and would likely have led to some enhanced rainfall in the region, but the author has learned of no damage or casualties resulting from this tropical cyclone. If any come to light later they will be reported in a future summary. *********************************************************************** NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea Activity for December: 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 December ------------------------------------------------- As the month of December opened the remnants of Tropical Cyclone 03B (which had reached hurricane intensity in November) were moving west- ward across the Arabian Sea. The system briefly regained minimal tropical storm intensity on the 3rd but had dissipated by the 6th several hundred miles off the coast of Somalia. The final NIO tropical cyclone of the year formed on Christmas Day east of Sri Lanka and struck the island as a hurricane on the 26th. The system then began to weaken, moved over the southern tip of India, and had dissipated by the 29th. Tropical Cyclone (TC-04B) 25 - 28 December -------------------------- Almost exactly a month after the last Bay of Bengal storm formed, another tropical cyclone formed in the Bay and also reached minimal hurricane intensity. TC-03B in November had struck southeastern India near Pondicherry, but this month's TC-04B followed a very low-latitude track and became the first tropical cyclone to strike the island nation of Sri Lanka since TC-10B struck the island with 55-kt winds on 12 November 1992. That particular storm left 13 persons dead in Sri Lanka, and later claimed over 200 lives in extreme southern India where it struck with 70-kt winds on the 13th. (This information was gleaned from some of Jack Beven's Weekly Global Tropical Cyclone Summaries, which were the predecessors to the current series of monthly summaries.) TC-04B was the first tropical cyclone of hurricane intensity in the Bay of Bengal in the month of December since TC-08B in 1996. (In 1998 TC-08A reached minimal hurricane intensity in the Arabian Sea in mid-December.) Because of its very low latitude (the northern tip is just south of 10N), and also by virtue of its being located in a basin with a low frequency of tropical cyclone formation, Sri Lanka only rarely receives a direct strike by one of these storms. At present the author does not know the last occasion prior to 2000 when a tropical cyclone of full hurricane intensity struck the island. No hurricanes have struck Sri Lanka since at least 1987. In November, 1978, a hurricane (designated as TC 21-78 by JTWC) struck the island with 95-kt winds near Batticaloa where sustained winds of 85 kts were reported two hours before the center reached the coast. More than 1000 lives were lost in that cyclone and many thousands of acres of crops were destroyed by the storm's winds, rain, and associated storm surge. (This information was taken from the 1978 Annual Typhoon Report from JTWC.) A STWO issued by JTWC at 1800 UTC on 21 December mentioned that an area of convection had developed and persisted very deep in the tropics in the central Bay of Bengal. The convection was in a region of weak vertical wind shear and a QuikScat pass indicated a possible LLCC. The disturbance remained quasi-stationary over the next couple of days, and by the 23rd central convection had increased and a mid-level cyclonic circulation had begun to develop. The system had moved westward and was located about 240 nm east of Sri Lanka at 23/0700 UTC when the first of two Formation Alerts was issued. The disturbance continued to slowly become better organized and a second Formation Alert was issued at 24/0700 UTC when the LLCC was located approximately 140 nm east of Sri Lanka. A 23/2338 UTC QuikScat pass indicated that the weak LLCC was located south of the main convection and JTWC estimated the maximum winds at 20-25 kts. The STWO issued at 24/1800 UTC noted that animated satellite imagery depicted a decrease in overall organization with some weakening of the convection; however, this trend apparently soon reversed itself: at 0600 UTC on the 25th JTWC issued the first warning on TC-04B with an initial warning intensity of 40 kts. The cyclone was located about 135 nm east of Sri Lanka and was drifting westward at 2 kts. Satellite imagery indicated that the LLCC had moved under the deep convection, thus leading to the increase in Dvorak numbers. A subtropical ridge to the north steered the storm slowly westward as it steadily intensified. The MSW had reached 55 kts by 1800 UTC and animated infrared imagery showed improving organization with good outflow in all quadrants. A 25/1602 UTC SSM/I pass depicted the primary convective band wrapping tightly into the system center. The center of TC-04B made landfall around 0600 UTC on 26 December in eastern Sri Lanka near Trincomalee with the MSW estimated at 65 kts. Although the cyclone weakened some while over land, it maintained its organization rather well. By 0600 UTC on the 27th the storm's center had emerged back over water along the western coast of Sri Lanka with the MSW estimated at 50 kts. The cyclone was forecast to slowly re-intensify for at least the next 48 hours, but this failed to happen. The intensity was decreased to 45 kts at 1800 UTC as satellite imagery had indicated weakening convection and decreasing organization during the previous few hours. The center of TC-04B was located about 120 nm northwest of Colombo, Sri Lanka, but most of the deep convection lay to the west-northwest of the center over southern India. By 0600 UTC on 28 December the system had reached the coast of extreme southern India and was centered about 25 nm northeast of Cape Comorin. Convection had continued to weaken and become less organized, and most of the deeper convection was sheared to the west-northwest of the LLCC. JTWC decreased the MSW to 35 kts at 0600 UTC, and issued the final warning on the system at 1800 UTC with the rapidly weakening center still over land about 40 nm north-northwest of Cape Comorin. What little convection remained was very weak and displaced well north of the system's center; satellite imagery showed primarily low- and mid-level clouds near the center. Even though only a minimal hurricane at landfall, the cyclone was quite destructive to Sri Lanka. Fortunately the death toll was low: seven fatalities was the highest reported number available to the author. However, over 75,000 families were left homeless (upwards of half a million individuals) in the districts of Ampara, Batticaloa, Mannar, Anuradhapura, Trinacomalee, and Polonnaruwa. The fishing village of Pulmudai was reportedly destroyed, and about 20,000 hectares of rice fields were damaged. Many of the affected areas had already been experiencing flooding due to monsoon rains and the cyclone served to exacerbate the flooding. (In the Ampara district 94,000 persons had been rendered homeless in late November due to flooding from monsoon rains.) There was some wind-related damage reported: several police stations and military camps had their roofs blown off due to strong winds gusting between 80 and 95 kts (more than likely estimated values). Also, apparently many homes experienced the loss of their roofs--a report indicated that tens of thousands of people were being housed in temporary shelters due to the winds sweeping away the roofs of their houses. In southern India, heavy rains reportedly fell in the Tuticorin region of Tamil Nadu state but no damage or casualties were mentioned in the press report. *********************************************************************** SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E Activity for December: No tropical cyclones *********************************************************************** NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E Activity for December: 1 severe tropical cyclone NOTE: The primary sources of information for Australian Region tropical cyclones are the warnings and bulletins issued by the three TCWC's at Perth, Darwin, and Brisbane. Information gleaned from JTWC's warnings was used as a supplement for times when it was impossible to obtain Australian bulletins and for comparison purposes. References to sustained winds should be understood as being based on a 10-min averaging period unless otherwise noted. A description of the Australian Cyclone Severity Scale, which is alluded to in the narrative below, can be found in Chris Landsea's FAQ on HRD's website: or on Michael Bath's Australian Severe Weather site: A special thanks is due to Mark Kersemakers of the Darwin TCWC for forwarding to me a summary of Tropical Cyclone Sam. Also, a special thanks to Carl Smith, a cyclone enthusiast who lives on Queensland's Gold Coast, for sending me a report he'd written on Sam from which I extracted some information. Much tropical cyclone-related information can be found on Carl's website: Northwest Australia/Southeast Indian Ocean Tropical Activity for December ------------------------------------------ The 2000-2001 tropical cyclone season in northwestern Australia got off to a start in a manner remarkably similar to the previous year. In early December, 1999, a very intense Cyclone John made landfall at Whim Creek, just east of Roebourne, as a Category 5 cyclone on the Australian Cyclone Severity Scale. This year's Cyclone Sam made land- fall also as a Category 5 cyclone (perhaps only slightly less intense than John) in Western Australia, but about 400 km to the east near Bidyadanga, southwest of Broome. (In 1999 a much weaker Tropical Cyclone Ilsa followed on the heels of John and made landfall a few days later in the same general area as this year's Tropical Cyclone Sam.) Actually, this was the third consecutive year to feature a December Category 5 cyclone making landfall in northwestern Australia. In December, 1998, Severe Tropical Cyclone Thelma battered Darwin with hurricane-force gusts and eventually made landfall at peak intensity along the Kimberley coast near the Northern Territory/Western Australia border. However, the 1998-1999 season had gotten off to a very early start with Cyclone Zelia forming farther out in the Southeast Indian Ocean in early October, followed by Alison in November and Billy in early December. Severe Tropical Cyclone Sam (TC-03S) 3 - 10 December ------------------------------------- The daily TWO from Darwin on 28 November mentioned that a broad area of low pressure had formed in the southeastern Arafura Sea west of the Cape York Peninsula. The LOW moved steadily westward for the next few days, passing north of the Northern Territory's Top End on the 29th and 30th, and by 1 December had reached a point in the Timor Sea about 230 nm northwest of Darwin and became quasi-stationary. A STWO issued by JTWC at 0300 UTC on 1 December indicated persistent convection in the area with fair outflow aloft. The Darwin TCWC began issuing tropical cyclone advices on the LOW at 5:00 pm CST on the 2nd (0730 UTC). The center of the still-broad circulation was located about 250 nm northwest of Darwin and was moving slowly southwestward. The STWO issued by JTWC at 1800 UTC on the 2nd indicated that outflow had improved and convection was becoming increasingly organized. Darwin began issuing High Seas gale warnings at 03/0600 UTC as the LOW continued to show signs of further development. The system moved generally very slowly southward over the next 24 hours and had reached the Kimberley coast by 0130 UTC on the 4th about 90 km (50 nm) east of Kalumburu. The center of the LOW tracked farther inland as it moved west-southwestward over the north Kimberley region. This track over land delayed the strengthening of the system, but once it moved back out over the warm Timor Sea waters, intensification proceeded at a steady pace. At 04/1800 UTC the center of the LOW was relocated north of the previous position to a point on the coastline about 180 km (100 nm) west-southwest of Kulumburu and 480 km (260 nm) northeast of Broome. The center was moving westward at 8 kts out into the Timor Sea. JTWC issued a Formation Alert at 04/1700 UTC, noting that the system was beneath the subtropical ridge and the development potential was considered good. The Perth TCWC assumed warning responsibility for the developing tropical cyclone at 04/2200 UTC as the center had moved west of 125E, and JTWC issued their first warning on TC-03S at 05/0000 UTC. The LOW was christened Tropical Cyclone Sam at 0400 UTC when it was centered about 75 nm north of Kuri Bay. The 10-min avg MSW was estimated to be around 40-45 kts. A 05/0958 SSM/I pass depicted a partially-exposed LLCC with convection displaced to the southwest. At the time Sam was north of the subtropical ridge axis under 15 to 25-kt northeasterly flow which was inhibiting development somewhat. The cyclone's intensity increased slowly for about 48 hours after being upgraded as it moved westward off the coast of Western Australia. Perth had increased the MSW to 55 kts by 2200 UTC on the 5th while JTWC's 1-min avg MSW was lower at 45 kts. However, JTWC estimated that the peak 1-min avg MSW had reached 55 kts by 06/1200 UTC. Sam's convective organization was improving and the storm was under favorable outflow aloft. A 06/0945 UTC SSM/I pass depicted a primary band of convection on the west wrapping into the northern quadrant of the system. At 1000 UTC on 6 December the cyclone's center was located approximately 170 nm north-northwest of Broome and moving toward the west-southwest at 5 kts. Sam's motion became increasingly southwestward during the evening (local) of the 6th. JTWC increased the 1-min avg MSW to 65 kts in the 07/0000 UTC warning based on satellite intensity estimates. Animated satellite imagery depicted increasing organization with a tightly- curved banding eye feature, a feature which had been noted earlier in microwave imagery. Perth's 10-min avg MSW was in good agreement: at 2200 UTC the estimate was 60 kts and the intensity was increased to 70 kts at 0400 UTC on the 7th, making Sam a Category 3 cyclone. The storm's center was then located about 65 nm northwest of Broome, or approximately 90 nm north-northwest of Bidyadanga, moving south- southwestward at 6 kts. During the late afternoon and evening (local) of 7 December Tropical Cyclone Sam began to intensify rapidly into a very severe cyclone. Perth upgraded the storm to a Category 4 cyclone at 1400 UTC (10:00 pm WST) and JTWC issued an offtime warning at 1800 UTC (JTWC normally issues warnings every 12 hours for Southern Hemisphere cyclones) to upgrade the MSW to 115 kts (up from 85 kts six hours earlier). Sam was sporting a well-defined 25-nm diameter eye at this time, although the storm was under some moderate vertical wind shear. (According to Mark Lander, around 07/1200 UTC the objective (digital) Dvorak rating for Sam reached T7.7!) The cyclone, after moving to the south-southwest, slowly jogged for awhile a bit more to the southwest before turning southeastward toward the coast. By 2000 UTC Perth had upgraded Sam to a Category 5 cyclone with an estimated CP of 920 nm and peak gusts estimated at 150 kts-- corresponding to a maximum 10-min avg wind of about 105 kts. Sam became almost stationary for a few hours about 65 nm northwest of Bidyadanga before commencing the southeastward movement that would carry it inland near the same community. At 0600 UTC on 8 December JTWC increased the 1-min avg MSW estimate to the peak value for the storm of 125 kts. The eye, well-defined and about 15 nm in diameter, was centered about 40 nm west-northwest of Bidyadanga, moving south- eastward at about 7 kts. The center of Severe Tropical Cyclone Sam crossed the coast just west of Bidyadanga around 1100 UTC (7:00 pm WST) on 8 December at its peak intensity. By 1600 UTC the eye had just about completed crossing the coast with the center inland to the south of Bidyadanga. Convection was beginning to weaken but radar imagery revealed a strong convective band northwest of the eye moving onshore near La Grange Bay. After making landfall the powerful cyclone continued moving south- eastward across the Great Sandy Desert as it slowly weakened. By 08/2200 UTC the center of the by-now Category 3 cyclone was located approximately 100 km south-southeast of Bidyadanga with peak gusts estimated at 110 kts. The final warning from JTWC was issued at 0600 UTC on 9 December with the MSW (1-min avg) still estimated at 65 kts. The warning noted that although convection was weakening, Sam still maintained some tightly-wrapped banding features. At 09/1000 UTC Sam's center was located 165 km northeast of Telfer and moving southeastward at 15 km/hr. Gusts exceeding hurricane force were still reported to be occurring near the center. The storm was down- graded to a Category 1 cyclone at 1300 UTC, and the final advice was issued on the weakening Sam at 1200 UTC on the 10th (8:00 pm WST), placing the center about 305 km east of Telfer. The advice indicated that there was still a possibility of a few gales with gusts reaching near 50 kts, but those were expected to moderate within a few hours. The remnants of Tropical Cyclone Sam persisted as a rain-bearing LOW for several days as it drifted eastward across northern Australia. Most of the 200-plus residents of the Aboriginal community of Bidyadanga were evacuated before the cyclone struck; however, press reports indicated that around 30 persons elected to remain behind and ride out the storm (although a later report mentioned that only three people refused to leave). Major structural damage appeared to be light with only a few buildings severely damaged, but many trees, power lines, sheds and fences were downed. The Anna Plains homestead station south of Broome was extensively damaged with staff quarters and sheds demolished. The station also lost power and water during the cyclone. Shelamar reported 520 mm of rainfall in the 48 hours ending at 9:00 am on 11 December, but most of this likely fell within a 24-hour period since the community was evacuated for a time and no 24-hour reading was taken. There was a report from Reuters that 163 illegal immigrants were feared drowned after two boats which had left Indonesia, bound for the Ashmore Islands (about 600 km off the coast of northwestern Australia), had been caught in Tropical Cyclone Sam and sank. A Japanese tanker reportedly picked up four survivors. This story has apparently never been confirmed, but there is no reason to doubt it since five boatloads of illegal immigrants did arrive in Australian waters in the week following the cyclone, proving that refugee-laden boats were in the area at the time. *********************************************************************** NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E Activity for December: 1 tropical LOW NOTE: The primary sources of information for Australian Region tropical cyclones are the warnings and bulletins issued by the three TCWC's at Perth, Darwin, and Brisbane. Information gleaned from JTWC's warnings was used as a supplement for times when it was impossible to obtain Australian bulletins and for comparison purposes. References to sustained winds should be understood as being based on a 10-min averaging period unless otherwise noted. Northeast Australia/Coral Sea Tropical Activity for December ------------------------------ No tropical cyclones formed in the Gulf of Carpentaria or Coral Sea during December; however, a tropical LOW formed on the 4th very near the tip of the Cape York peninsula and moved southwestward across the Gulf, making landfall around 0130 UTC on the 6th about 90 nm south- west of Alyangula or about 75 nm west-northwest of Port McArthur. The Brisbane TCWC issued three advices on the LOW before passing warning responsibility to Darwin. It was initially felt that the LOW might develop into a tropical cyclone, but by the time Darwin had assumed responsibility for issuing advices, the system had not gotten any better organized and was rapidly approaching the coastline in the southwestern Gulf of Carpentaria region. One factor which probably worked against this LOW's developing into a cyclone was its somewhat rapid rate of movement: for most of its life it moved southwestward across the Gulf at speeds of around 16 to 19 kts--rather fast for that part of the world--which likely made it more difficult for the system to consolidate its convection, and if nothing else, significantly decreased the time spent over the warm waters of the Gulf before making landfall. *********************************************************************** SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E Activity for December: 2 tropical depressions NOTE: 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 December -------------------------------------------- There were no tropical cyclones in the South Pacific basin during December, but the Nadi TCWC did issue gale warnings on two tropical depressions during the month. TD-01F formed about 200 nm west of Fiji on 11 December and moved eastward toward the islands. Apparently no gales actually occurred during this phase of the system's life and advisories were discontinued at 12/2100 UTC as the system was moving southeastward into an area of increased shear and cooler SSTs. Gale warnings, however, were re-initiated at 14/0000 UTC. The depression by this time had moved rapidly eastward and was located about 300 nm east-southeast of the Kingdom of Tonga. Some gales were occurring over an extensive area along the southern periphery of the system, but it seems likely that the depression was not fully tropical during its latter warning phase. The system remained quasi-stationary in the area until the final gale warning was issued at 15/1200 UTC. A report from the Office for the Coordination of Humanitarian Affairs stated that a tropical depression (which undoubtedly must have been TD-01F) crossed Fiji and brought gusty winds, thunderstorms and bands of continuous rainfall. Rivers reportedly burst their banks, flooding low-lying areas. Two persons drowned and two others were reported missing at sea. Roads and bridges were submerged in some areas and power outages were reported. Minor landslides occurred and damage was reported to root crops and other vegetables. Another tropical depression (likely more of a hybrid) formed far to the southeast of Tahiti (about 375 nm west-northwest of Pitcairn) on 18 December. This system was accompanied by some peripheral gales well north and east of the center. The system moved fairly quickly eastward and the final warning, issued at 19/1200 UTC, placed the center about 275 nm east of Pitcairn Island. *********************************************************************** EXTRA FEATURE In order to shorten the amount of typing in preparing the narrative material, I have been in the habit of freely using abbreviations and acronyms. I have tried to define most of these with the first usage in a given summary, but I may have missed one now and then. Most of these are probably understood by a majority of readers but perhaps a few aren't clear to some. To remedy this I developed a Glossary of Abbreviations and Acronyms which I first included in the July, 1998 summary. I don't normally include the Glossary in most months in order to help keep them from being too long. If anyone would like to receive a copy of the Glossary, please e-mail me and I'll be happy to send them a copy. *********************************************************************** AUTHOR'S NOTE: This summary should be considered a very preliminary overview of the tropical cyclones that occur in each month. The cyclone tracks (provided separately) will generally be based upon operational warnings issued by the various tropical cyclone warning centers. The information contained therein may differ somewhat from the tracking and intensity information obtained from a "best-track" file which is based on a detailed post-seasonal analysis of all available data. Information on where to find official "best-track" files from the various warning centers will be passed along from time to time. The track files are not being sent via e-mail. They can be retrieved 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 December as an example: dec00.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: dec00.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 I have discovered that JTWC now has available on its website the complete Annual Tropical Cyclone Report (ATCR) for 1999 (1998-1999 season for the Southern Hemisphere). Also, 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. The URL is: Prepared by: Gary Padgett E-mail: garyp@alaweb.com Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays) *********************************************************************** *********************************************************************** 03.22.01 / Typhoon2000.com