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Hurricane Henri Forecast Discussion Number 23
2021-08-21 16:42:06| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sat Aug 21 2021 000 WTNT43 KNHC 211442 TCDAT3 Hurricane Henri Discussion Number 23 NWS National Hurricane Center Miami FL AL082021 1100 AM EDT Sat Aug 21 2021 The Air Force Reserve and NOAA Hurricane Hunters have been investigating Henri this morning and continue to provide very valuable data. The Air Force aircraft measured a peak flight-level wind of 82 kt at 700 mb, which easily supports hurricane strength, but the initial intensity is set at 65 kt as a blend of these data and somewhat lower SFMR winds. In addition, aircraft data indicate that the minimum pressure has fallen to 991 mb. The NOAA tail Doppler radar data indicate that the storm is becoming more vertically aligned and that a more symmetric eyewall appears to be forming. In addition, dropsonde data from the NOAA Gulfstream IV aircraft flying around Henri indicate that the 34- and 50-kt wind radii are a little larger than previously estimated in the southeastern quadrant. NOAA buoy 41001 located in the northeastern quadrant of the hurricane has recently reported 18 ft. seas. Henri is moving north-northeastward, or 020 degrees, at 12 kt. The steering pattern appears fairly well established now with a cut off low located over the central Appalachians and a ridge building to the east and northeast of Henri. This pattern should cause the storm to accelerate to the north or north-northeast today followed by a slight bend to the left on Sunday. The latest run of the GFS has shifted to the east, but overall the models are focused in on landfall being between central Long Island and Rhode Island on Sunday. However, users are reminded to not focus on the center itself, as impacts will extend well away from the center, especially to the east. The new NHC track forecast is a little to the east of the previous one and very near the best-performing models, the consensus aids. The environment looks favorable for Henri to continue to gain strength through tonight with low shear, upper-level divergence associated with the upper-level trough, and warm SSTs. In fact, the GFS and HWRF models show the minimum pressure dropping by 15 mb or more during that time period. By early Sunday, Henri is predicted to cross the north wall of the Gulf Stream and that should cause some weakening, but Henri is forecast to be at or near hurricane strength at landfall. Once the center moves inland over the northeast United States, rapid weakening is expected. Henri is forecast to become post-tropical in 48-60 hours and dissipate in 3 to 4 days. Key Messages: 1. Dangerous storm surge inundation is expected to begin late tonight or Sunday in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Warning has been issued. Dangerous storm surge is possible beginning late tonight or Sunday in western portions of Long Island and Connecticut in the Storm Surge Watch area. Residents in these areas should follow any advice given by local officials. 2. Hurricane conditions are expected to begin late tonight or Sunday in portions of Long Island, Connecticut, and Rhode Island, where a Hurricane Warning is in effect. Tropical storm conditions will begin in these areas tonight. 3. Heavy rainfall may lead to considerable flash, urban, and small stream flooding, along with the potential for widespread minor and isolated moderate river flooding, over portions of Long Island, New England, southeast New York and northern New Jersey. 4. Swells from Henri will continue to affect much of the east coast of the U.S. during the next day or two. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 34.4N 72.5W 65 KT 75 MPH 12H 22/0000Z 36.9N 71.9W 75 KT 85 MPH 24H 22/1200Z 39.7N 71.9W 70 KT 80 MPH 36H 23/0000Z 41.3N 72.6W 60 KT 70 MPH...INLAND 48H 23/1200Z 42.4N 72.9W 35 KT 40 MPH...INLAND 60H 24/0000Z 43.1N 71.9W 25 KT 30 MPH...POST-TROP/INLAND 72H 24/1200Z 43.8N 69.2W 25 KT 30 MPH...POST-TROP/INLAND 96H 25/1200Z...DISSIPATED $$ Forecaster Cangialosi
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