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| #1158253 (Received by flhurricane at: 4:52 AM 21.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 12 NWS National Hurricane Center Miami FL AL202023 500 AM AST Sat Oct 21 2023 Mosaic radar data from Martinique, Guadeloupe, and Barbados show that Tammy`s core is passing just to the east of Martinique and Dominica. The eyewall has become more pronounced during the past several hours although it is open on the south side. In infrared satellite imagery, the hurricane has a relatively small CDO and a prominent trailing convective band to the south, but no evidence of an eye. Based on earlier Air Force Reserve reconnaissance data, Tammy`s initial intensity remains 70 kt. Aircraft fixes and the radar data indicate that Tammy has finally turned northwestward at 305/8 kt. A strong mid-latitude trough moving off the east coast of the United States is eroding the western portion of the Atlantic subtropical ridge, which should cause Tammy to continue northwestward across the Leeward Islands through tonight and early Sunday, and then turn north-northwestward and northward Sunday and Monday. For the first 3 days of the forecast, the new NHC track prediction is nearly on top of the previous forecast and is close to the HCCA consensus aids. There has been a dramatic change in the global model solutions beyond day 3. Some models (the ECMWF and UKMET) show the trough completely bypassing Tammy and leaving the cyclone to stall north of Puerto Rico and the Virgin Islands, while others (the GFS and Canadian) initially show Tammy turning northeastward but then interacting with a shortwave trough and slowing down over the western Atlantic. The NHC track forecast has been shifted significantly westward on days 4 and 5 to account for these latest model trends. Tammy will continue moving over very warm waters of 29-30 degrees Celsius during the next few days, but the storm will also continue to contend with some moderate westerly or southwesterly vertical shear. Fluctuations in intensity will be possible during the next few days depending on if the oceanic or atmospheric factors win out, but all in all little change in strength is predicted during the next 3 to 4 days. Some weakening is possible at the end of the forecast period due to a more significant increase in shear. KEY MESSAGES: 1. Hurricane and tropical storm conditions are expected in portions of the Leeward and northern Windward Islands through Sunday. 2. Heavy rains from Tammy will affect the Windward and Leeward Islands today, spreading into the British and U.S. Virgin Islands and eastern Puerto Rico as early as 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 21/0900Z 15.2N 60.4W 70 KT 80 MPH 12H 21/1800Z 16.3N 61.3W 75 KT 85 MPH 24H 22/0600Z 17.8N 62.4W 75 KT 85 MPH 36H 22/1800Z 19.3N 63.3W 75 KT 85 MPH 48H 23/0600Z 20.6N 64.0W 75 KT 85 MPH 60H 23/1800Z 21.9N 64.2W 75 KT 85 MPH 72H 24/0600Z 22.8N 64.0W 75 KT 85 MPH 96H 25/0600Z 24.5N 63.1W 70 KT 80 MPH 120H 26/0600Z 27.0N 62.1W 60 KT 70 MPH $$ Forecaster Berg |
