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Tropical Storm Isaias Forecast Discussion Number 24
2020-08-03 04:43:45| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sun Aug 02 2020 000 WTNT44 KNHC 030243 TCDAT4 Tropical Storm Isaias Discussion Number 24 NWS National Hurricane Center Miami FL AL092020 1100 PM EDT Sun Aug 02 2020 Isais has not become better organized on satellite and radar imagery at this time. The cyclone continues to produce vigorous deep convection but this convection continues to be displaced to the northeast of the center, and convective banding features are ill-defined. Air Force Hurricane Hunter observations show that the central pressure has not fallen since earlier today, and flight-level and SFMR-observed surface wind measurements from the aircraft indicate that the intensity remains near 60 kt. Although Isais will be moving through an environment of fairly strong southwesterly shear during the next day or so, it will also be traversing the warm waters of the Gulf Stream with its high oceanic heat content. The latter factor could result in the system becoming a hurricane near landfall. The official forecast is close to the intensity consensus, which keeps Isaias just below hurricane strength. It should be emphasized that there is little difference between a strong tropical storm or a category 1 hurricane, in terms of impacts. After landfall, the interaction with land and strong shear should result in steady weakening. Based on the global models, the cyclone is likely to become an extratropical cyclone after it moves into Canada and dissipate over the north Atlantic shortly thereafter. The motion continues to be slightly west of due north or 345/8 kt. There has been no significant change to the track forecast reasoning. Over the next couple of days, Isaias is expected to accelerate north-northeastward on the east side of a large 500 mb trough over the eastern United States and then turn northeastward in 3 to 4 days as it moves through the mid-latitude westerlies. The official track forecast is very close to the previous one and similar to the latest corrected dynamical model consensus. This is between the GFS, which shows a slightly faster motion and the ECMWF, which is slightly slower. Key Messages: 1. There is the danger of life-threatening storm surge inundation of 2 to 4 feet above ground level from Edisto Beach South Carolina to Cape Fear North Carolina along the immediate coastline and adjacent waterways. Life-threatening storm surge is possible along the North Carolina coast from Cape Fear to Duck. Residents in these areas should follow advice given by local emergency officials. 2. Tropical storm conditions will spread northward within the Tropical Storm Warning area from Florida to Maryland through early Tuesday. Isaias is expected to be near hurricane strength when it reaches the coast of northern South Carolina and southern North Carolina Monday night, and strong tropical storm force winds are likely with hurricane conditions possible in the Hurricane Watch area. 3. Heavy rainfall from Isaias will continue to result in potentially life-threatening flash flooding in the Northwest Bahamas through tonight. Flash and urban flooding, some of which may be significant in the eastern Carolinas and the mid-Atlantic, is expected through midweek along and near the path of Isaias across the East Coast of the United States. Widespread minor to moderate river flooding is possible across portions of the Carolinas and the mid-Atlantic. 4. Tropical storm conditions are forecast to spread northward across the remainder of the U.S east coast on Tuesday and early Wednesday. A tropical storm watch is in effect through Long Island Sound and additional watches and warnings will likely be issued on Monday. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 28.5N 79.8W 60 KT 70 MPH 12H 03/1200Z 29.7N 80.0W 60 KT 70 MPH 24H 04/0000Z 32.2N 79.3W 60 KT 70 MPH 36H 04/1200Z 35.9N 77.3W 55 KT 65 MPH...INLAND 48H 05/0000Z 40.5N 74.0W 40 KT 45 MPH...INLAND 60H 05/1200Z 45.5N 70.0W 35 KT 40 MPH...INLAND 72H 06/0000Z 50.0N 65.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 07/0000Z 55.5N 56.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/0000Z...DISSIPATED $$ Forecaster Pasch
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