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Tropical Storm Henri Forecast Discussion Number 7
2021-08-17 16:35:30| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Aug 17 2021 000 WTNT43 KNHC 171435 TCDAT3 Tropical Storm Henri Discussion Number 7 NWS National Hurricane Center Miami FL AL082021 1100 AM AST Tue Aug 17 2021 Henri remains a sheared tropical storm. Geostationary satellite images and microwave data show a relatively large area of deep convection (~200 miles across), but the center of the storm is located near the western edge of the thunderstorms due to ongoing northwesterly vertical wind shear. The latest Dvorak estimates have been steady at 3.0/45 kt from TAFB and SAB, and based on that data, the initial intensity is held at 45 kt. The center of Henri is located roughly 130 miles south-southeast of Bermuda currently, and this will likely be as close as the storm gets to the island. The tropical storm is gradually turning to the west, as expected, and the initial motion is estimated to be 255/5 kt. A subtropical ridge over the western Atlantic is building eastward to the north of Henri, and this feature should steer the storm westward at a slightly faster pace during the next two or three days. After that time, the ridge is expected to weaken and shift farther east as a cut off low or negatively-tilted trough develops over the northeast U.S. This change in the steering pattern should cause Henri to turn northeastward between Bermuda and the east coast of the U.S in the 72-120 h period. The NHC track forecast is a little faster than the previous one in the short term and farther west than the previous one from days 3-5, trending toward the latest consensus models. The northwesterly shear currently affecting Henri is expected to subside later today, and that should allow the storm to gain strength during the next 12-24 hours. However, a round of moderate northerly shear is expected to setup over Henri during the 24-96 hour period. Although this shear would typically cause some weakening, the combination of warm SSTs and increasing mid-level moisture could offset the negative influences of the shear. Therefore, no change in strength is predicted beyond the 24 h period. Some of the models suggest that the shear could lessen again this weekend, so although not explicitly forecast, some strengthening is possible then. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 30.4N 64.3W 45 KT 50 MPH 12H 18/0000Z 30.4N 65.1W 50 KT 60 MPH 24H 18/1200Z 30.3N 66.5W 55 KT 65 MPH 36H 19/0000Z 30.3N 68.2W 55 KT 65 MPH 48H 19/1200Z 30.4N 69.7W 55 KT 65 MPH 60H 20/0000Z 30.7N 70.6W 55 KT 65 MPH 72H 20/1200Z 31.6N 71.3W 55 KT 65 MPH 96H 21/1200Z 34.1N 69.6W 55 KT 65 MPH 120H 22/1200Z 37.4N 66.0W 55 KT 65 MPH $$ Forecaster Cangialosi
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