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| #1010379 (Received by flhurricane at: 12:08 AM 31.Jul.2020) TCDAT4 Hurricane Isaias Special Discussion Number 12 NWS National Hurricane Center Miami FL AL092020 1200 AM EDT Fri Jul 31 2020 An Air Force Reserve Hurricane Hunter found that Isaias has become a hurricane. Maximum flight-level winds so far were 87 kt at 850 mb, with believable SFMR values of at least 65 kt. A blend of these values gives an initial wind speed of 70 kt. Some further strengthening is likely over the next 24 hours before increasing southwesterly shear could weaken the system. The intensity forecast is modified upward from 5-10 kt through 48 hours and unchanged after that time. There are no changes to the previous track forecast. Key Messages: 1. Isaias will produce heavy rains and potentially life-threatening flash flooding and mudslides across the Dominican Republic, northern Haiti, Turks and Caicos, and the Bahamas. 2. Hurricane conditions and dangerous storm surge are expected in portions of the southeastern Bahamas overnight, central and northwestern Bahamas late Friday and Saturday, and Hurricane Warnings are in effect for these areas. Preparations to protect life and property should be rushed to completion. 3. Tropical storm conditions are possible along portions of the Florida east coast beginning Saturday, and a Tropical Storm Watch is in effect. While storm surge watches are not currently needed for this area, they may be required on Friday if the forecast track shifts closer to the coast. Heavy rains associated with Isaias may begin to affect South Florida and east-Central Florida beginning late Friday night, potentially resulting in isolated flash and urban flooding, especially in low-lying and poorly drained areas. 4. There is a risk of impacts from winds, heavy rainfall, and storm surge late this weekend from the northeastern Florida coast and spreading northward along the remainder of the U.S. east coast through early next week. The details of the track and intensity forecast remain uncertain, and it is too soon to determine the magnitude and location of these potential impacts, but interests along the entire U.S. east coast should monitor the progress of Isaias and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 31/0400Z 20.4N 72.2W 70 KT 80 MPH 12H 31/1200Z 21.6N 73.9W 70 KT 80 MPH 24H 01/0000Z 23.5N 76.1W 75 KT 85 MPH 36H 01/1200Z 25.2N 77.8W 75 KT 85 MPH 48H 02/0000Z 26.7N 79.0W 70 KT 80 MPH 60H 02/1200Z 28.3N 79.6W 65 KT 75 MPH 72H 03/0000Z 30.0N 79.5W 65 KT 75 MPH 96H 04/0000Z 34.6N 76.8W 65 KT 75 MPH 120H 05/0000Z 42.0N 69.0W 60 KT 70 MPH $$ Forecaster Blake |