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Tropical Storm Henri Forecast Discussion Number 22
2021-08-21 10:53:53| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Sat Aug 21 2021 000 WTNT43 KNHC 210853 TCDAT3 Tropical Storm Henri Discussion Number 22 NWS National Hurricane Center Miami FL AL082021 500 AM EDT Sat Aug 21 2021 An earlier GMI satellite microwave image continued to indicate that Henri's low-level center was still located near the northwestern edge of the convective canopy. However, more recent geostationary satellite imagery shows that the convection is beginning to wrap around the northeastern and eastern portions of the circulation suggesting that the anticipated decrease in shear is occuring, and that Henri may be on the verge of strengthening. The latest subjective satellite intensity estimates from SAB and TAFB remained unchanged so the initial intensity remains 60 kt, in agreement with those estimates and the earlier aircraft data. The next reconnaissance aircraft mission should be in the storm around 1200 UTC this morning. Henri is moving north-northeastward or 015/10 kt. A mid- to upper-level low and associated trough over the Appalachians and Ohio Valley should steer Henri north-northeastward at a faster forward speed today. As Henri moves around the eastern portion of the upper-low, the storm is forecast to turn north-northwestward tonight. This motion will bring the center of Henri near or over portions of Long Island and Southern New England on Sunday and into the northeastern United States Sunday night. After that time, the cyclone should turn east-northeastward as it becomes caught in the mid-latitude westerlies. The latest dynamical model envelope continues to narrow for the first 24 to 36 hours of the forecast period and only small adjustments were needed to that portion of the track. After that time, the guidance has trended to taking Henri farther inland over the Northeastern United States, and the NHC forecast as been modified accordingly. Decreasing shear, upper-level divergence associated with the trough to Henri's west, and warm SSTs should allow the cyclone to strengthen during the next 12-18 hours. Although not explicitly shown in the intensity forecast, Henri could still peak around 75 kt later today or this evening. After that time, cooler waters are likely to cause a gradual reduction in intensity, however, Henri is forecast to be at or near hurricane strength at landfall. Once the center moves inland over the Northeast United States, a faster rate of filling is anticipated. The system is forecast to become post-tropical in about 60 hours, and it will likely dissipate around day 4, if not a little sooner. The updated intensity forecast is near the upper-end of the intensity guidance during the first 12-24 hours, and is close to the Decay-SHIPS model thereafter. 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 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 and Connecticut, where a Hurricane Warning has been issued. Hurricane conditions are possible late tonight or Sunday across portions of Rhode Island. 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. through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 33.1N 73.2W 60 KT 70 MPH 12H 21/1800Z 35.6N 72.3W 70 KT 80 MPH 24H 22/0600Z 38.8N 72.0W 70 KT 80 MPH 36H 22/1800Z 40.9N 72.7W 60 KT 70 MPH...INLAND 48H 23/0600Z 42.1N 73.6W 35 KT 40 MPH...INLAND 60H 23/1800Z 42.8N 73.3W 25 KT 30 MPH...POST-TROP/INLAND 72H 24/0600Z 43.3N 71.5W 25 KT 30 MPH...POST-TROP/INLAND 96H 25/0600Z 44.5N 62.5W 25 KT 30 MPH...POST-TROPICAL 120H 26/0600Z...DISSIPATED $$ Forecaster Brown
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