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| #1200280 (Received by flhurricane at: 10:57 AM 26.Sep.2024) TCDAT4 Hurricane Helene Discussion Number 13 NWS National Hurricane Center Miami FL AL092024 1000 AM CDT Thu Sep 26 2024 Helene is gaining strength as it approaches the Florida Big Bend. A large eye has become apparent in satellite images, and that feature has been gradually clearing out over the past few hours. Convective banding is wrapping around the eye, and recent microwave images and reports from the NOAA and Air Force Hurricane Hunter aircraft indicate than an eyewall is almost completely closed. The minimum pressure has been dropping steadily to near 960 mb, and based on the aircraft flight-level wind data, the initial intensity is estimated to have increased to 90 kt. There have been several reports of tropical-storm-force winds occurring in portions of South Florida and the Florida Keys during the past few hours. The large hurricane is picking up speed and has turned slightly to the north-northeast. The latest initial motion is 025/12 kt. A notably faster north-northeastward motion is expected through landfall, which is expected to occur in the Florida Big Bend region this evening. After Helene moves inland, it is forecast to track over Georgia and then slow down or stall over the Tennessee Valley when it merges with a mid- to upper-level low pressure system. Only minor changes were made to the previous NHC track forecast. Significant intensification is expected until Helene reaches the coast since the overall atmospheric and oceanic conditions will remain conducive. The amount of strengthening will likely depend on how much the inner core can contract and consolidate. The HWRF and HMON models show significant strengthening to category 4 status, while most of the other models are a little lower. The main message is that Helene will likely make landfall as a large major hurricane in the Florida Big Bend this evening, and all preparations in the hurricane warning area should be rushed to completion. It should also be re-emphasized that Helene is a very large hurricane. In fact, comparing the system with previous hurricanes in the Gulf of Mexico over the past couple of decades, Helene is at the upper bound in terms of size. As a result, storm surge, wind, and rainfall impacts will extend far away from the center and well outside the forecast cone, particularly on the east side. In addition, the fast forward speed when Helene moves inland will result in a far inland penetration of strong winds over parts of the southeastern United States, including strong gusts over higher terrain of the southern Appalachians. Accordingly, a higher-than-normal gust factor is indicated in the official forecast while Helene is inland. KEY MESSAGES: 1. A catastrophic and deadly storm surge is likely along portions of the Florida Big Bend coast, where inundation could reach as high as 20 feet above ground level, along with destructive waves. There is also a danger of life-threatening storm surge along the remainder of the west coast of the Florida Peninsula. Residents in those areas should follow advice given by local officials and evacuate if told to do so. 2. Potentially catastrophic hurricane-force winds are expected within the eyewall of Helene when it makes landfall in the Florida Big Bend region this evening. Preparations to protect life and property should be rushed to completion. Damaging and life-threatening hurricane-force winds, especially in gusts, will penetrate well inland over portions of northern Florida and southern Georgia later today and tonight where Hurricane Warnings are in effect. Strong wind gusts are also likely farther north across portions of northern Georgia and the Carolinas, particularly over the higher terrain of the southern Appalachians. 3. Catastrophic and life-threatening flash and urban flooding, including numerous significant landslides, is expected across portions of the southern Appalachians through Friday. Considerable to locally catastrophic flash and urban flooding is likely for northwestern and northern Florida and the Southeast through Friday. Widespread significant river flooding and isolated major river flooding are likely. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 25.5N 85.5W 90 KT 105 MPH 12H 27/0000Z 28.8N 84.3W 105 KT 120 MPH 24H 27/1200Z 33.9N 84.5W 55 KT 65 MPH...INLAND 36H 28/0000Z 36.4N 86.6W 30 KT 35 MPH...POST-TROP/EXTRATROP 48H 28/1200Z 36.5N 87.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 60H 29/0000Z 36.3N 87.6W 20 KT 25 MPH...POST-TROP/EXTRATROP 72H 29/1200Z 36.2N 87.2W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 30/1200Z...DISSIPATED $$ Forecaster Cangialosi |
