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| #1200085 (Received by flhurricane at: 5:00 PM 25.Sep.2024) TCDAT4 Hurricane Helene Discussion Number 10 NWS National Hurricane Center Miami FL AL092024 400 PM CDT Wed Sep 25 2024 A ragged eye is becoming apparent in visible satellite imagery and has also been observed in recent radar data from Cancun and western Cuba. Based on the improved structure, the initial intensity is set at 75 kt, which is at the high end of the satellite intensity estimates. This is also supported by the earlier Air Force Reserve reconnaissance mission, which measured a peak 700-mb flight-level wind of 81 kt. Helene has turned northward (355/9 kt) and is expected to accelerate toward the north or north-northeast during the next 24-36 hours as it moves across the Gulf of Mexico and crosses the Florida Big Bend coast Thursday evening. After landfall, the system is forecast to interact with a deep-layer trough to the west and turn northwestward with a decrease in speed over the Tennessee Valley. The environment appears primed for significant strengthening while Helene moves across the Gulf of Mexico. The forecast track more or less runs along the axis of the Loop Current during the next 24 hours, where ocean temperatures are about 30 degrees Celsius. In addition, Helene will be moving through an environment of low vertical shear and strong upper-level divergence. Some of the Rapid Intensification (RI) indices, particular DTOPS, respond to this environment by indicating at least a 90 percent chance of a 35-kt increase in intensity over the next 24 hours. The NHC intensity forecast now shows an intensity of 115 kt (Category 4) at 24 hours, which is mirrored by several of the regional hurricane models and the SHIPS guidance. It should be noted that additional strengthening is possible beyond 24 hours before Helene makes landfall Thursday evening. Helene is forecast to be a large major hurricane when it reaches the Big Bend coast of Florida. As a result, storm surge, wind, and rainfall impacts will extend well away from the center and 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. A higher-than-normal gust factor has been 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 late Thursday. Preparations to protect life and property should be completed by early Thursday before tropical storm conditions arrive. Damaging and life-threatening hurricane-force winds, especially in gusts, will penetrate well inland over portions of northern Florida and southern Georgia late Thursday and Thursday night 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 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 minor to moderate river flooding is likely, and isolated major river flooding is possible. 4. Hurricane and tropical storm conditions are expected over northeastern portions of the Yucatan Peninsula of Mexico this evening where Tropical Storm and Hurricane Warnings are in effect. Tropical storm conditions are occurring over portions of western Cuba within the Tropical Storm Warning area, and hurricane conditions are possible this evening within the Hurricane Watch area. Helene will bring heavy rain to portions of the western Caribbean with potentially significant flooding across western Cuba and the northeastern Yucatan Peninsula into early Thursday. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 22.5N 86.6W 75 KT 85 MPH 12H 26/0600Z 24.1N 86.2W 95 KT 110 MPH 24H 26/1800Z 27.4N 85.2W 115 KT 130 MPH 36H 27/0600Z 32.1N 84.6W 70 KT 80 MPH...INLAND 48H 27/1800Z 36.1N 86.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 60H 28/0600Z 37.1N 88.1W 25 KT 30 MPH...POST-TROP/EXTRATROP 72H 28/1800Z 36.8N 88.7W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 29/1800Z 37.0N 88.0W 15 KT 15 MPH...POST-TROP/EXTRATROP 120H 30/1800Z...DISSIPATED $$ Forecaster Berg |
