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Tropical Storm Isaias Forecast Discussion Number 25
2020-08-03 10:56:48| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Mon Aug 03 2020 000 WTNT44 KNHC 030856 TCDAT4 Tropical Storm Isaias Discussion Number 25 NWS National Hurricane Center Miami FL AL092020 500 AM EDT Mon Aug 03 2020 Isaias continues to produce an area of vigorous convection near and to the northeast of its low-level center. Overnight radar data from Melbourne and Jacksonville have shown a transient mid-level eye feature that is located northeast of the low-level center. The earlier Air Force Reserve Hurricane Hunter aircraft flew near that feature before departing the storm and found 700-mb flight-level winds of 71 kt, with the highest SFMR winds still around 60 kt, which is the basis for the initial wind speed for this advisory. An Air Force Reserve and NOAA Hurricane Hunter aircraft will be investigating Isaias within the next several hours. The vertical wind shear that has been plaguing Isaias is forecast to abate slightly today as the storm turns north-northeastward. All of the intensity models shows some slight strengthening during the next 12 hours, and the global models also indicate some deepening. As a result, the updated NHC intensity forecast calls for Isaias to regain hurricane status before the system moves over the coast of the Carolinas. The new intensity forecast has necessitated the issuance of a hurricane warning for a portion of the coasts of northern South Carolina and southern North Carolina. After landfall, Isaias is forecast to gradually weaken, but given the fast forward motion of the storm, strong winds are expected to spread northward along the coast of the Mid-Atlantic and Northeast United States. The cyclone is forecast to be absorbed by a larger extratropical low over Canada in 3-4 days. Isaias is moving northward or 355/8 kt. The track forecast reasoning remains the same as before. The tropical storm is expected to accelerate north-northeastward to northeastward ahead of a large mid-level trough over the eastern United States during the next couple of days. The dynamical models are in good agreement except for some slight differences in the forward speed of Isaias. The NHC track forecast is near the multi-model consensus aids, which have once again trended slightly faster. Key Messages: 1. There is the danger of life-threatening storm surge inundation along portions of the immediate coastline and adjacent waterways of northeastern South Carolina and southern North Carolina. 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. Isaias is forecast to regain hurricane strength before it reaches the coast of northeastern South Carolina and southern North Carolina, and hurricane conditions are expected in the Hurricane Warning by this evening. Preparations should be rushed to completion. 3. Tropical storm conditions are expected to spread northward within the Tropical Storm Warning area from Florida to portions of southern New England through Tuesday afternoon. Tropical storm conditions are possible across other portions of New England within the Tropical Storm Watch area by early Wednesday. Additional watches or warnings may be required later today. 4. Heavy rainfall will result in flash and urban flooding, some of which may be significant in the eastern Carolinas and the mid-Atlantic, 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. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 29.7N 79.9W 60 KT 70 MPH 12H 03/1800Z 31.3N 79.6W 65 KT 75 MPH 24H 04/0600Z 34.8N 78.1W 60 KT 70 MPH...INLAND 36H 04/1800Z 39.4N 75.2W 55 KT 65 MPH...INLAND 48H 05/0600Z 44.4N 71.5W 35 KT 40 MPH...INLAND 60H 05/1800Z 48.6N 68.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 06/0600Z 52.0N 65.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 07/0600Z...DISSIPATED $$ Forecaster Brown/Berg
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