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Hurricane Isaias Forecast Discussion Number 17
2020-08-01 10:55:42| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Sat Aug 01 2020 000 WTNT44 KNHC 010855 TCDAT4 Hurricane Isaias Discussion Number 17 NWS National Hurricane Center Miami FL AL092020 500 AM EDT Sat Aug 01 2020 Isaias has a somewhat ragged appearance in satellite imagery this morning, likely due to the impact of westerly shear and dry air entrainment. The area of central convection has shrunk in size, although radar data from the Bahamas shows some banding near the center and occasional attempts to wrap up an eyewall. Also, a dry slot is now present in the eastern semicircle between the central convection and the outer banding. The last Hurricane Hunter mission indicated that the maximum winds had increased to near 75 kt, so that is maintained for this advisory. NOAA and Air Force Reserve Hurricane Hunter aircraft are scheduled to investigate the storm during the next several hours. The initial motion is now northwestward or 315/10 kt. The track forecast philosophy remains unchanged, as Isais should continue to move northwestward on the southwest side of a mid-level ridge today and begin to turn north-northwestward through a weakness in the ridge on Sunday. After that, the storm should recurve into the mid-latitude westerlies, with a turn toward the north-northeast and northeast with an increase in forward speed likely. The track guidance envelope has shifted a little to the east near the Florida coast and calls for a slower forward motion that the previous guidance. Thus, the new forecast track has been adjusted a little east of, and slower than, the previous track. The hurricane is currently undergoing about 25 kt of westerly vertical shear, and some mid-level dry air is present west of the center. This combination should prevent any more intensification, and, while Isaias is expected to remain a hurricane as it passes near the Florida coast, at least slight weakening should occur during this time. Current indications from the global models are that the storm will continue to experience strong shear as it recurves, and thus the intensity forecast follows the previous forecast in calling for weakening during this time. Key Messages: 1. Hurricane conditions and dangerous storm surge are expected in portions of the Bahamas through Saturday, and Hurricane Warnings are in effect. 2. Hurricane conditions are expected along portions of the Florida east coast late Saturday and Saturday night, and a Hurricane Warning is in effect. 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 in these areas should follow advice given by local emergency officials. 4. Isaias will produce heavy rains and potentially life-threatening flash and urban flooding, especially in low-lying and poorly drained areas, across South to east-Central Florida, and across the Carolinas to the mid Atlantic. Minor river flooding is possible across portions of the Carolinas and into Virginia early next week. 5. There is a risk of impacts from winds, heavy rainfall, and storm surge spreading along much of the the U.S. east coast through early next week, and interests there should monitor the progress of Isaias and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 23.9N 77.1W 75 KT 85 MPH 12H 01/1800Z 25.0N 78.2W 75 KT 85 MPH 24H 02/0600Z 26.3N 79.2W 70 KT 80 MPH 36H 02/1800Z 27.6N 79.9W 70 KT 80 MPH 48H 03/0600Z 29.1N 80.3W 65 KT 75 MPH 60H 03/1800Z 31.2N 79.8W 60 KT 70 MPH 72H 04/0600Z 34.0N 77.8W 60 KT 70 MPH 96H 05/0600Z 41.5N 71.4W 50 KT 60 MPH...INLAND 120H 06/0600Z 47.5N 61.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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