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| #1010370 (Received by flhurricane at: 10:39 PM 30.Jul.2020) TCDAT4 Tropical Storm Isaias Discussion Number 11 NWS National Hurricane Center Miami FL AL092020 1100 PM EDT Thu Jul 30 2020 Isaias is beginning to form a small Central Dense Overcast, but much of the deep convection is situated over the eastern portion of the circulation. Water vapor imagery suggests that upper-level outflow is modest to the northwest of the cyclone. The southern portion of the system is still interacting with Hispaniola at this time. Dvorak intensity estimates are 45 kt from SAB and 55 kt from TAFB so the current maximum wind speed is 50 kt for this advisory. An Air Force Hurricane Hunter aircraft is headed for Isaias and should soon provide a more precise intensity estimate. Although southwesterly shear may limit strengthening of the system during the next couple of days, the environment should still be conducive enough for Isaias to become a hurricane in 24 to 36 hours. The official intensity forecast is similar to the previous one and a little above the model consensus. The initial motion is a somewhat uncertain 305/16 kt. There are no basic changes to the track forecast or reasoning from the previous advisory. Isaias should continue to move generally northwestward on the southern and southwestern side of a subtropical high pressure area for the next day or so. Then, as an approaching mid-tropospheric trough erodes the high, a gradual turn toward the north-northwest and north should occur. In 3 to 5 days, the trough should cause Isaias to turn toward the north-northeast and northeast and accelerate. The official track forecast is close to the previous one and follows the latest simple and corrected dynamical model consensus tracks. 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 or tropical storm conditions and dangerous storm surge are expected in portions of the northwestern and central Bahamas late Friday and Saturday, and Hurricane and Tropical Storm Warnings, respectively, are in effect for these areas. Preparations to protect life and property should be rushed to completion. Tropical storm conditions will continue to spread across portions of the Dominican Republic, Haiti, the Turks and Caicos and the southeastern Bahamas tonight through Friday, and Tropical Storm Warnings are in effect for these areas. 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 31/0300Z 20.5N 71.9W 50 KT 60 MPH 12H 31/1200Z 21.6N 73.9W 55 KT 65 MPH 24H 01/0000Z 23.5N 76.1W 60 KT 70 MPH 36H 01/1200Z 25.2N 77.8W 65 KT 75 MPH 48H 02/0000Z 26.7N 79.0W 65 KT 75 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 Pasch |
