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| #1199889 (Received by flhurricane at: 5:00 PM 24.Sep.2024) TCDAT4 Tropical Storm Helene Discussion Number 6 NWS National Hurricane Center Miami FL AL092024 500 PM EDT Tue Sep 24 2024 Deep convection is gradually filling in within Helene's circulation, and the well-defined center that formed earlier this morning is now obscured by cloudiness and showers. Data from NOAA buoy indicate that the central pressure has fallen to 995 mb, and the initial intensity is therefore estimated to be 45 kt. NOAA and the Air Force Reserve Hurricane Hunters will be investigating Helene this evening to provide more information about the storm's intensity and structure. With the center formation this morning, Helene has taken a short-term jog to the west-northwest (300/10 kt). The storm is expected to turn northwestward by tonight and then northward on Wednesday as high pressure over Florida shifts eastward, and a deep-layer trough digs southward over the Lower Mississippi Valley. The NHC track forecast has been shifted westward during the first 24 hours to account for the recent motion, and Helene's center could get very close to the northeastern coast of the Yucatan Peninsula Wednesday morning. After that time, however, the NHC track forecast is relatively unchanged from the previous prediction, except for being a little bit slower based on the latest guidance. Helene is expected to accelerate while it moves northward across the eastern Gulf of Mexico and approaches the Florida Gulf coast. Warm sea surface temperatures, decreasing shear, and strong upper-level divergence are likely to foster Helene's strengthening while it moves across the northwestern Caribbean Sea and eastern Gulf of Mexico. The statistical-dynamical SHIPS/LGEM models, as well as the regional hurricane models, continue to show Helene reaching major hurricane intensity while over the eastern Gulf of Mexico, and that continues to be shown in the NHC forecast. Helene could maintain that level of intensity until it reaches the Gulf coast of Florida. Of equal importance to the forecast intensity is Helene's forecast size. Helene's forecast radii are at the 90th percentile of major hurricane size at similar latitudes, and therefore storm surge, wind, and rainfall impacts will likely extend well away from the center and outside the forecast cone, particularly on the east side. In addition, the fast forward speed while it crosses the coast will likely result in farther inland penetration of strong winds over parts of the southeastern United States after landfall. KEY MESSAGES: 1. Helene is forecast to intensify and be near hurricane strength when it passes near the northeastern coast of the Yucatan Peninsula on Wednesday, where a Hurricane Warning is in effect. 2. Helene is expected to rapidly intensify and grow in size over the eastern Gulf of Mexico. There is a danger of life-threatening storm surge along the entire west coast of the Florida Peninsula and Florida Big Bend. The highest inundation levels are expected along the coast of the Florida Big Bend. Residents in those areas should follow advice given by local officials and evacuate if told to do so. 3. Damaging hurricane-force winds are expected along portions of coast of the Florida Big Bend, where a Hurricane Warning is now in effect. Preparations to protect life and property should be complete by early Thursday since tropical storm conditions are expected to begin within this area on Thursday. 4. Helene will bring heavy rain to portions of the western Caribbean with potentially significant flooding and mudslides across western Cuba. Considerable flash and urban flooding is expected across portions of Florida, the Southeast, southern Appalachians, and the Tennessee Valley Wednesday through Friday. This includes the risk of landslides across the southern Appalachians. Widespread minor to moderate river flooding is likely, and isolated major river flooding is possible. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 19.7N 84.7W 45 KT 50 MPH 12H 25/0600Z 20.4N 86.0W 55 KT 65 MPH 24H 25/1800Z 21.7N 86.6W 65 KT 75 MPH 36H 26/0600Z 23.7N 86.1W 80 KT 90 MPH 48H 26/1800Z 27.0N 84.9W 100 KT 115 MPH 60H 27/0600Z 31.5N 84.0W 60 KT 70 MPH...INLAND 72H 27/1800Z 35.5N 84.8W 30 KT 35 MPH...INLAND 96H 28/1800Z 38.2N 89.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 29/1800Z...DISSIPATED $$ Forecaster Berg |
