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| #1057532 (Received by flhurricane at: 10:51 AM 18.Aug.2021) TCDAT3 Tropical Storm Henri Discussion Number 11 NWS National Hurricane Center Miami FL AL082021 1100 AM AST Wed Aug 18 2021 Deep convection has been increasing during the past several hours in association with Henri, and the cloud pattern mostly consists of a central dense overcast with some fragmented bands around it. The Dvorak estimates are steady at 3.5/55 kt from TAFB and SAB, and therefore, the initial intensity is held at that value. However, the latest automated Dvorak values from CIMSS at the University of Wisconsin are higher, so it is possible that Henri could be slightly stronger. An SSMIS pass from 1124 UTC showed some southward tilt of the vortex with height and revealed a small mid-level eye feature. Henri continues to move just south of due west at 7 kt. The storm is expected to move westward during the next day or so as it moves in the flow on the south or southeast side of a mid-level ridge. This ridge is expected to slide eastward by Friday as a mid- to upper-level low develops over the Ohio Valley and northeastern U.S. In response, Henri is expected to turn northward or north- northeastward on Friday and continue in that direction through the weekend. One complicating factor is that several of the models show a ridge building over the northwestern Atlantic and Atlantic Canada, which could cause the storm to stay on a more northward track closer to New England than currently forecast. The spread in the models for Henri`s future track is quite large, with some guidance as far west as Long Island and as far east as 62W longitude. Overall, the models continue to walk left each cycle, and the NHC track forecast has again been shifted in that direction. NOAA Gulfstream IV missions and special weather balloon soundings have been scheduled, and it is hoped that this additional data will help the models handle the evolving steering pattern. Given the uncertainty in the longer range track forecasts, users should be prepared for additional adjustments to the NHC track forecast in future forecast cycles. The storm is currently in an environment of about 15-20 kt of northerly wind shear according to the SHIPS model and analyses from CIMSS at the University of Wisconsin. Since the shear is expected to persist or become a little stronger during the next couple of days, little change in strength is predicted during that time period. After that time, the shear is expected to lessen and that should allow Henri to strengthen to a hurricane by the weekend. Some weakening is shown by the end of the period when Henri is forecast to be moving over cooler waters. The NHC intensity forecast is largely an update of the previous one and is just a little lower than the consensus aids. Key Messages: 1. Swells from Henri could 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. 2. Uncertainty in the track forecast for Henri this weekend and early next week is larger than usual, and there is some risk of direct impacts from Henri in portions of the northeastern U.S. and Atlantic Canada during that time. Interests in these areas should follow updates to the forecast through the next several days. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 30.0N 66.6W 55 KT 65 MPH 12H 19/0000Z 29.9N 67.9W 60 KT 70 MPH 24H 19/1200Z 29.8N 69.8W 60 KT 70 MPH 36H 20/0000Z 30.1N 71.4W 60 KT 70 MPH 48H 20/1200Z 30.7N 72.4W 60 KT 70 MPH 60H 21/0000Z 32.1N 72.5W 65 KT 75 MPH 72H 21/1200Z 34.2N 71.5W 75 KT 85 MPH 96H 22/1200Z 38.0N 69.6W 75 KT 85 MPH 120H 23/1200Z 41.0N 67.0W 65 KT 75 MPH $$ Forecaster Cangialosi |
