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| #1158282 (Received by flhurricane at: 10:53 AM 21.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 13 NWS National Hurricane Center Miami FL AL202023 1100 AM AST Sat Oct 21 2023 The center of Tammy is now located just to the east-southeast of Guadeloupe in the Leeward Islands. Satellite and radar data indicate that the core of the hurricane is quite compact and despite its close proximity to the islands, the strong winds remain just offshore. The NOAA and Air Force Hurricane Hunters have been investigating Tammy this morning, and a combination of the data they have collected indicate that the hurricane has strengthened a little. The initial intensity is nudged upward to 75 kt based on maximum 700 mb flight-level winds of 86 kt and a peak SFMR wind of 74 kt. However, as noted above, the hurricane-force winds are occurring over a small region very near the center. The hurricane has turned to the right over the past several hours, and the initial motion is now northwestward, 325 degrees, at 7 kt. A continued northwestward motion is expected during the next 12-24 hours, taking the core of Tammy over or just east of the Leeward Islands during that time. After the hurricane clears the islands, a turn to the north seems likely when the system moves in the flow between a ridge over the central Atlantic and a large trough over the western Atlantic. There is a significant amount of spread in the models in the days 3-5 time frame, which seems to be associated with model differences in the magnitude of the trough and vertical depth/intensity of Tammy. The NHC track forecast is a little to the right and slower than the previous one based on the initial position/motion and latest model guidance. However, given that the spread in the model positions of Tammy are about 900 miles at day 5, confidence is low in Tammy`s long range track. Tammy will likely fluctuate in strength over the next few days while it remains in mixed environmental conditions of very warm SSTs and moderate wind shear. The NHC intensity forecast is a touch higher than the previous one and generally near the IVCN and HCCA models. Gradual weakening seems likely by the middle of next week when it moves into a region of stronger shear, but the intensity forecast at that range is of low confidence since its future strength will likely be correlated to the track. KEY MESSAGES: 1. Hurricane and tropical storm conditions are expected in portions of the Leeward and northern Windward Islands through early Sunday. 2. Heavy rains from Tammy will affect the Lesser Antilles north of Martinique today, spreading across the British and U.S. Virgin Islands and possibly eastern Puerto Rico on Sunday. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. 3. A storm surge could produce coastal flooding in areas of onshore winds as the center of Tammy moves near or over the Leeward Islands. Near the coast, the surge will be accompanied by large and dangerous waves. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 16.0N 60.7W 75 KT 85 MPH 12H 22/0000Z 17.0N 61.6W 75 KT 85 MPH 24H 22/1200Z 18.6N 62.5W 80 KT 90 MPH 36H 23/0000Z 20.0N 63.3W 80 KT 90 MPH 48H 23/1200Z 21.3N 63.8W 80 KT 90 MPH 60H 24/0000Z 22.3N 63.8W 80 KT 90 MPH 72H 24/1200Z 23.2N 63.5W 80 KT 90 MPH 96H 25/1200Z 24.9N 62.7W 75 KT 85 MPH 120H 26/1200Z 27.3N 62.0W 65 KT 75 MPH $$ Forecaster Cangialosi |
