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| #1192583 (Received by flhurricane at: 4:48 AM 07.Aug.2024) TCDAT4 Tropical Storm Debby Discussion Number 20 NWS National Hurricane Center Miami FL AL042024 500 AM EDT Wed Aug 07 2024 Debby's circulation consists of a nearly 60 nm wide convection-free region near the center, which is drifting eastward off the coast of South Carolina. Moderate to deep convection is organized in broken bands well away from the center, with the strongest band currently feeding into eastern North Carolina. The storm appears to have strengthened slightly now that a greater proportion of the circulation is back over water, and the initial intensity is set at 40 kt based on a 0143 UTC ASCAT-B pass. The longer-term motion is slowly eastward, or 085/4 kt. Although Debby is expected to maintain a slow motion for the next 24 hours or so, a mid-level ridge over the western and central Atlantic should cause the storm to turn northward today, with the center reaching the coast of South Carolina by tonight. Debby should then accelerate toward the north and northeast beginning on Thursday over the eastern United States and eastern Canada, ahead of a deep-layer trough moving across the Upper Midwest and Great Lakes region. No changes were required to the new NHC track forecast, which lies on top of the previous forecast and down the middle of the guidance envelope. Debby's structure does not argue for any type of significant strengthening, but warm ocean waters of 29 degrees Celsius and low shear could allow the wind field to strengthen a bit over the next 24 hours while the circulation remains over water. A peak intensity of 45 kt is shown at 12 and 24 hours, which is generally in line with the bulk of the intensity guidance. Weakening is forecast to begin by 36 hours once the center moves inland, and global model fields and phase-space diagrams indicate that Debby is likely to be absorbed by a front and become extratropical by 60 hours over the Mid-Atlantic region of the United States. Key Messages: 1. Heavy rainfall across portions of eastern South Carolina and southeast North Carolina is expected to persist through Thursday which would broaden areas of considerable flooding. Expected heavy rainfall will likely result in considerable flooding impacts from the Piedmont of the Carolinas, portions of the Mid-Atlantic States, and Vermont through Saturday morning. 2. Tropical storm conditions will spread northward along the southeast U.S. coast from South Carolina to North Carolina through Thursday. Tropical storm warnings and watches are in effect for portions of that area. 3. A dangerous storm surge is possible along the coast of South Carolina and southeastern North Carolina from South Santee River to Cape Fear. Residents in that area should follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 31.9N 79.5W 40 KT 45 MPH 12H 07/1800Z 32.3N 79.3W 45 KT 50 MPH 24H 08/0600Z 32.9N 79.5W 45 KT 50 MPH 36H 08/1800Z 34.1N 79.8W 35 KT 40 MPH...INLAND 48H 09/0600Z 36.0N 79.7W 30 KT 35 MPH...INLAND 60H 09/1800Z 39.2N 77.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 10/0600Z 43.8N 73.9W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 11/0600Z 50.8N 62.1W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 12/0600Z 53.9N 53.5W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg |
