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Tropical Storm Henri Forecast Discussion Number 15
2021-08-19 16:35:47| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Thu Aug 19 2021 000 WTNT43 KNHC 191435 TCDAT3 Tropical Storm Henri Discussion Number 15 NWS National Hurricane Center Miami FL AL082021 1100 AM EDT Thu Aug 19 2021 Henri is not as well organized as it was yesterday. Microwave images show that the vortex is titled to the south with height due to about 25 kt of north-northeasterly wind shear. The system is still producing a fair amount of deep convection, however, and the cloud pattern resembles a central dense overcast with banding features limited to the south side of the circulation. The Dvorak estimates continue to range from 55 kt to 65 kt, and therefore, the initial intensity is again held at 60 kt. The Air Force Reserve Hurricane Hunters will be investigating Henri later today, and the data the aircraft collects will be very helpful in assessing the storm's structure and strength. The tropical storm is moving just south of due west at 9 kt. Henri is expected to move generally westward through tonight as the storm remains on the south side of a mid-level ridge. On Friday, however, a trough is expected to cut off over the Ohio Valley and mid-Atlantic region of the U.S. while a ridge amplifies to the east of Henri over the western Atlantic. A combination of these features should cause Henri to turn northward on Friday and accelerate in that direction over the weekend. By early next week, the ridge is expected to weaken, which should cause Henri to turn more toward the east. The models are in much better agreement than they were yesterday and their solutions are clustering around southern New England on Sunday and Monday. The NHC track forecast is just a tad to the left of the previous one and lies near the typically best-performing models, the various consensus aids. In addition to the Air Force aircraft that flies through the storm, the NOAA Gulfstream IV jet will also be flying around Henri later today to help assess the environmental conditions and gather data for the numerical models. It is hoped that these data will help the models more accurately predict the future track of the storm. The current north-northeasterly shear over Henri is forecast to continue for about another day, and given the degraded structure of the system it seems unlikely that the storm will strengthen during that time period. However, the shear is expected to decrease on Friday and it will remain quite low through the weekend. Therefore, strengthening to a hurricane is expected during that time period. Once Henri crosses the north wall of the Gulf Stream in a few days, steady weakening is predicted. The NHC intensity forecast is just an update of the previous one and lies near the middle of the guidance envelope. It should be noted that as Henri gains latitude and moves near New England, the wind field is expected to expand. Therefore, users are reminded to not focus on the exact forecast points as impacts will extend far from the center. Key Messages: 1. Henri is forecast to be near the northeast coast of the U.S. on Sunday and Monday, and the risks of storm surge, wind, and rain impacts in portions of southern New England and eastern Long Island are increasing. Watches will likely be required for portions of this area on Friday. 2. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 29.5N 70.5W 60 KT 70 MPH 12H 20/0000Z 29.7N 71.9W 60 KT 70 MPH 24H 20/1200Z 30.4N 72.9W 60 KT 70 MPH 36H 21/0000Z 31.9N 72.9W 65 KT 75 MPH 48H 21/1200Z 34.4N 72.0W 75 KT 85 MPH 60H 22/0000Z 37.3N 70.7W 80 KT 90 MPH 72H 22/1200Z 39.6N 70.0W 75 KT 85 MPH 96H 23/1200Z 41.6N 69.7W 55 KT 65 MPH 120H 24/1200Z 42.3N 67.0W 45 KT 50 MPH $$ Forecaster Cangialosi
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