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| #1150557 (Received by flhurricane at: 4:50 AM 31.Aug.2023) TCDAT5 Tropical Storm Idalia Discussion Number 19 NWS National Hurricane Center Miami FL AL102023 500 AM EDT Thu Aug 31 2023 Surface observations from around 0600 UTC showed that the center of Idalia moved offshore of the coast of northeastern South Carolina. Strong southwesterly vertical wind shear has displaced the deep convective bands and heavy rainfall well north and northeast of the center over eastern North Carolina and the adjacent Atlantic. A partial ASCAT-B overpass over the southeastern portion of the circulation revealed winds of 40-45 kt and given that instrument`s typical undersampling, the initial wind speed is maintained at 50 kt for this advisory. Idalia has turned east-northeastward between a mid-level anticyclone over the Bahamas and a mid-tropospheric trough moving eastward over the northeastern United States. The anticyclone is forecast to retrograde over Florida during the next couple of days, causing Idalia to turn east-southeastward tonight and Friday. After that time, steering currents are predicted to weaken and the cyclone is expected to move very slowly to the southwest of Bermuda during the weekend. By early next week, another mid-latitude trough moving off the northeast U.S. coast should cause Idalia to begin moving northeastward, however there is still significant uncertainty in the details of the track forecast later in the period. Little change in strength is predicted today, but strong upper-level winds and drier mid-level air are likely to cause some gradual weakening by the weekend. Simulated satellite imagery from the GFS and ECMWF models suggest that the system could lose organized deep convection as soon as tonight, and Idalia could degenerate into a post-tropical cyclone in a day or so. However, the ECMWF does show a return of deep convection over the weekend so the official forecast continues to retain the system as a tropical storm throughout the foreast period. KEY MESSAGES: 1. Areas of flash, urban, and moderate river flooding, with considerable impacts, will continue across coastal North Carolina through today. 2. Coastal flooding is expected within the Storm Surge Watch area in North Carolina today. Residents in these areas should follow any advice given by local officials. 3. Tropical storm conditions are expected in northeastern South Carolina and portions of eastern North Carolina today. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 33.6N 78.0W 50 KT 60 MPH 12H 31/1800Z 34.0N 75.1W 50 KT 60 MPH 24H 01/0600Z 33.5N 71.7W 45 KT 50 MPH 36H 01/1800Z 32.4N 69.1W 45 KT 50 MPH 48H 02/0600Z 31.5N 68.0W 40 KT 45 MPH 60H 02/1800Z 31.2N 67.5W 40 KT 45 MPH 72H 03/0600Z 31.4N 66.6W 40 KT 45 MPH 96H 04/0600Z 33.1N 63.8W 40 KT 45 MPH 120H 05/0600Z 35.6N 61.4W 45 KT 50 MPH $$ Forecaster Brown |
