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Tropical Storm Henri Forecast Discussion Number 21
2021-08-21 05:00:19| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Aug 20 2021 000 WTNT43 KNHC 210300 TCDAT3 Tropical Storm Henri Discussion Number 21 NWS National Hurricane Center Miami FL AL082021 1100 PM EDT Fri Aug 20 2021 Satellite imagery shows that Henri is becoming better organized this evening, with the low-level center becoming more embedded in the convective overcast and an increase in convective banding. There has also been an increase in the anticyclonic outflow. However, reports from Air Force Reserve and NOAA Hurricane Hunter aircraft show that this has not yet resulted in strengthening, as the maximum winds remain about 60 kt to the southeast of the elongated center and the central pressure is in the 994-996 mb range. Henri has turned northward, and the initial motion is now 010/8. A deep-layer mid-latitude trough over the Appalachians and the Ohio Valley will cut off into a closed low during the next 12-24 h, while a ridge builds northward to the east and northeast of Henri. This evolution should cause the storm to move north-northeastward for 12-24 h, followed by a turn toward the north-northwest from 24-48 h. This motion should bring the center of Henri over the mid-Atlantic states or southern New England between 36-48 h. After 48 h, the cyclone should get caught up in the southern edge of the westerlies and turn generally eastward across southern New England and the Gulf of Maine. There has been little change in the direction of the forecast guidance since the last advisory, but the guidance is faster on this cycle through 48 h. Thus, the new track forecast, which lies close to the consensus models, is faster than the previous forecast through the 48 h point. A combination of decreasing shear, improved organization, and upper-level divergence associated with the trough to the west should allow Henri to strengthen for the next 24 h or so, and the new intensity forecast calls for a peak intensity of 75 kt. After 24 h, the center should move over cooler water, and weakening should start before landfall in the northeastern United States. However, the cyclone is still expected to be at or near hurricane intensity at landfall. After landfall, Henri should weaken quickly and become post-tropical by the 72 h time. Dissipation is forecast between 96-120 h. The new intensity forecast follows the overall trend of the intensity guidance. Users are reminded to not focus on the exact forecast of the center of Henri since impacts will extend far from the center. Key Messages: 1. Dangerous storm surge inundation is expected to begin late Saturday night 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 Saturday night 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 Saturday night or Sunday in portions of Long Island and Connecticut, where a Hurricane Warning has been issued. Hurricane conditions are possible late Saturday night or Sunday across portions of Rhode Island and southeastern Massachusetts. 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 and New England Sunday into Monday. 4. Swells from Henri will continue to affect much of the east coast of the U.S. through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 32.3N 73.5W 60 KT 70 MPH 12H 21/1200Z 34.3N 72.8W 65 KT 75 MPH 24H 22/0000Z 37.7N 72.1W 75 KT 85 MPH 36H 22/1200Z 40.2N 72.6W 70 KT 80 MPH 48H 23/0000Z 41.4N 73.4W 50 KT 60 MPH...INLAND 60H 23/1200Z 42.2N 73.2W 35 KT 40 MPH...INLAND 72H 24/0000Z 42.7N 72.3W 30 KT 35 MPH...POST-TROP/INLAND 96H 25/0000Z 43.5N 67.0W 25 KT 30 MPH...POST-TROPICAL 120H 26/0000Z...DISSIPATED $$ Forecaster Beven
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