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Tropical Storm Isaias Forecast Discussion Number 20
2020-08-02 04:56:57| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat Aug 01 2020 000 WTNT44 KNHC 020256 TCDAT4 Tropical Storm Isaias Discussion Number 20 NWS National Hurricane Center Miami FL AL092020 1100 PM EDT Sat Aug 01 2020 Deep convection has increased this evening in a cluster to the east and northeast of the aircraft-observed center position. Radar data suggests a mid-level center or vorticity maximum in that area, which is between Grand Bahama and Andros Island. Observations from the Air Force Hurricane Hunters indicate that Isaias has not restrengthened thus far, but there is still a small window of opportunity for it to regain hurricane intensity Sunday while passing over the Gulf Stream waters. Synoptic surveillance data from the NOAA Gulfstream-IV aircraft indicate that the upper-level west-southwesterly flow over Isais will begin to increase by late Sunday. The resulting increase in shear and interaction with land should cause weakening beyond 24 hours, and the official intensity forecast is near or above the intensity model consensus. Assuming that the aforementioned mid-level feature is not the dominant center of circulation, the aircraft fixes give a motion estimate of about 310/8 kt. Isais has been moving northwestward along the southwestern periphery of a mid-level high pressure area. An approaching trough near the Ohio Valley is expected to cause the tropical cyclone to turn northward within 48 hours. After that, Isaias should accelerate north-northeastward to northeastward ahead of the trough, and move near or over the east coast of the United States. The official track forecast remains close to both the simple and corrected dynamic model consensus tracks, TVCN and HCCA respectively. Key Messages: 1. Hurricane conditions and dangerous storm surge will continue in portions of the northwest Bahamas through Sunday morning. 2. Hurricane conditions are expected along portions of the Florida east coast on Sunday with tropical storm conditions expected to begin late tonight. Preparations to protect life and property should be rushed to completion. 3. Dangerous storm surge is possible along the Florida east coast from Jupiter Inlet to Ponte Vedra Beach where water rises of 2 to 4 feet above ground level are possible along the immediate coastline and adjacent waterways. Residents there should follow advice given by local emergency officials. 4. Isaias will produce heavy rains and potentially life-threatening flash flooding in the Bahamas, and flash and urban flooding, especially in low-lying and poorly drained areas, along the east coast of the United States. Minor river flooding and isolated moderate river flooding is possible across portions of the Carolinas and mid Atlantic early next week. 5. Tropical storm watches and warnings are in effect for portions of the United States East Coast from northeast Florida to South Carolina. Additional watches and warnings will likely be issued on Sunday as Isaias is expected to move northward near or over the southeast and mid-Atlantic coasts early next week. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 25.5N 79.1W 60 KT 70 MPH 12H 02/1200Z 26.6N 79.9W 65 KT 75 MPH 24H 03/0000Z 28.0N 80.5W 65 KT 75 MPH...ON COAST 36H 03/1200Z 29.7N 80.8W 60 KT 70 MPH 48H 04/0000Z 32.0N 80.0W 55 KT 65 MPH 60H 04/1200Z 35.3N 78.1W 50 KT 60 MPH...INLAND 72H 05/0000Z 39.7N 74.8W 40 KT 45 MPH...INLAND 96H 06/0000Z 47.0N 66.0W 35 KT 40 MPH...POST-TROP/INLAND 120H 07/0000Z 51.5N 57.5W 30 KT 35 MPH...POST-TROP/INLAND $$ Forecaster Pasch
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