368 WTNT45 KNHC 301500 TCDAT5 Hurricane Idalia Discussion Number 16...Retransmitted NWS National Hurricane Center Miami FL AL102023 1100 AM EDT Wed Aug 30 2023 Although Idalia reached category 4 intensity early this morning over the far northeastern Gulf of Mexico, Air Force Reserve Hurricane Hunter data just before landfall indicated that the peak winds had started to decrease and the minimum pressure had begun to rise. This was likely due to an eyewall replacement cycle (which was shown by radar data) and an increase in shear over the hurricane. Idalia made landfall near Keaton Beach, Florida, as a category 3 hurricane around 1145 UTC, and it has been weakening quickly since then over northern Florida. WSR-88D Doppler velocities suggest that the maximum winds are now down to about 80 kt. Idalia is moving toward the north-northeast, or 030/17 kt. The hurricane is located between a subtropical ridging near the Greater Antilles and a deep-layer trough over the eastern United States. This pattern is expected to cause Idalia to turn toward the northeast and then east during the next 36 hours, and the track guidance is very good agreement on the center moving near the coasts of Georgia, South Carolina, and North Carolina through Thursday. Model spread increases beyond 36 hours, although there is not as much uncertainty as yesterday. None of the models shows the circulation curving back toward the U.S. anymore, but the guidance is suggestive that Idalia will likely slow down as it approaches Bermuda on days 3 through 5. During that period, the NHC track forecast is a blend of the previous forecast with the current HCCA and TVCX consensus aids. Relatively fast weakening is anticipated through the rest of the day. The intensity guidance is hovering right around the hurricane threshold at 12 hours, and the official forecast therefore conservatively shows a 65-kt hurricane near the Georgia/South Carolina border this evening. Idalia should become a tropical storm by tonight while moving near the coast of South Carolina. The intensity forecast is a little bit above the guidance at 24 and 36 hours to account for the possibility of a band of strong winds developing on the back side of Idalia near eastern North Carolina, associated with a nearby frontal boundary. Beyond 36 hours, the guidance suggests that Idalia's intensity is likely to hover between 45-50 kt through the end of the forecast period. KEY MESSAGES: 1. Significant impacts from storm surge will continue along the Gulf coast of Florida within the Storm Surge Warning through this evening. Dangerous storm surge is also expected along the southeastern U.S. coast within the Storm Surge Warning area tonight and Thursday. Residents in these areas should follow any advice given by local officials. 2. Damaging hurricane-force winds will occur where the core of Idalia moves across southern Georgia and southern South Carolina within the hurricane warning area through this evening. Residents in these areas should be prepared for long-duration power outages. Strong winds are also expected to spread northeastward across South Carolina and North Carolina through Thursday within the Tropical Storm Warning area. 3. Areas of flash, urban, and moderate river flooding, with considerable impacts, are expected from portions of North Florida through central Georgia and South Carolina, through eastern North Carolina into Thursday. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 30.6N 83.2W 80 KT 90 MPH...INLAND 12H 31/0000Z 32.4N 81.1W 65 KT 75 MPH...INLAND 24H 31/1200Z 33.8N 77.6W 55 KT 65 MPH...OVER WATER 36H 01/0000Z 33.9N 74.0W 50 KT 60 MPH 48H 01/1200Z 33.2N 71.1W 45 KT 50 MPH 60H 02/0000Z 32.4N 69.1W 45 KT 50 MPH 72H 02/1200Z 31.9N 68.0W 50 KT 60 MPH 96H 03/1200Z 31.4N 66.3W 50 KT 60 MPH 120H 04/1200Z 32.5N 63.3W 50 KT 60 MPH $$ Forecaster Berg