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| #1200153 (Received by flhurricane at: 11:06 PM 25.Sep.2024) TCDAT4 Hurricane Helene Discussion Number 11 NWS National Hurricane Center Miami FL AL092024 1000 PM CDT Wed Sep 25 2024 Satellite images show that Helene has a well-organized appearance, with numerous convective banding features. A ragged-looking eye feature is also apparent. However, reports from both Air Force and a NOAA Hurricane Hunter aircraft investigating the system suggest that the it lacks a well-defined inner core with a somewhat broad maximum wind field for now. The central pressure has dropped a little to around 972 mb. Given the slowly falling central pressure, the intensity is maintained at 75 kt for this advisory. Helene's structure and intensity will continue to be closely monitored by Hurricane Hunter aircraft tonight and Thursday. The hurricane continues moving northward with an estimated initial motion of 360/08 kt. For the next couple of days, the steering scenario for this system remains basically unchanged from the earlier advisory. The flow between a mid-tropospheric trough over the east-central United States and a ridge over the western Atlantic should result in Helene accelerating northward to north-northeastward during the next 24 to 36 hours. This motion will bring the center of Helene to the northeastern Gulf of Mexico coast in about 24 hours. The official track forecast through landfall is very similar to the previous NHC prediction and remains close to the corrected consensus guidance. After landfall, the trough to the northwest of the tropical cyclone becomes a cutoff low, and Helene should turn leftward as it rotates around the low. In 3-4 days, the system should become a shallow extratropical cyclone within weaker steering currents. Helene should be in an atmospheric and oceanic environment over the eastern Gulf of Mexico that will be very conducive for strengthening. The system is expected to traverse the Loop Current, which has especially high oceanic heat content. This, along with fairly low vertical wind shear and a moist mid- to lower- tropospheric air mass, should likely result in rapid intensification before landfall. The official forecast continues to call for the hurricane to reach category 4 status tomorrow. It should be noted that the HAFS-A and HAFS-B regional hurricane models show even more intensification than indicated here. 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 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 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 numerous 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 and isolated major river flooding are likely. 4. Tropical storm conditions are expected over portions of western Cuba within the Tropical Storm Warning area. Hurricane 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 26/0300Z 23.1N 86.6W 75 KT 85 MPH 12H 26/1200Z 25.4N 86.1W 95 KT 110 MPH 24H 27/0000Z 29.5N 84.5W 115 KT 130 MPH 36H 27/1200Z 34.3N 84.7W 50 KT 60 MPH...INLAND 48H 28/0000Z 36.7N 87.1W 30 KT 35 MPH...POST-TROP/EXTRATROP 60H 28/1200Z 36.8N 88.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 72H 29/0000Z 36.7N 87.0W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 30/0000Z 36.7N 84.9W 15 KT 15 MPH...POST-TROP/EXTRATROP 120H 01/0000Z...DISSIPATED $$ Forecaster Pasch |
