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Tropical Storm Henri Forecast Discussion Number 12
2021-08-18 22:49:34| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Aug 18 2021 356 WTNT43 KNHC 182049 TCDAT3 Tropical Storm Henri Discussion Number 12 NWS National Hurricane Center Miami FL AL082021 500 PM AST Wed Aug 18 2021 Henri appears a little better organized this afternoon. The storm still has a central dense overcast pattern and there have been hints of an eye evident in visible satellite images. Microwave images continue to show a mid-level eye feature, but the storm does not appear quite as well organized in the low-levels, and the vortex is still titled southward with height. The latest Dvorak estimates range from 55 to 67 kt, and based on that data the initial intensity is nudged up to 60 kt, just below hurricane strength. Henri is moving just south of due west at a slightly faster pace now, 265/8 kt. The storm is expected to continue westward for another 36 hours or so as it moves in the flow on the south side of a mid-level ridge. A gradual turn to the north is forecast to begin on Friday when a cutoff low forms over the Ohio Valley and the northeastern U.S. This general northward motion should continue through the weekend as another ridge builds to the east of Henri over the northwestern Atlantic. The models continue their westward shift, and the NHC track forecast has again been adjusted in that direction and no longer shows a northeastward motion out to sea. In particular, the westward adjustment at day 5 was a sizable 150 miles, and even with this shift the NHC forecast is still a little to the east of some of the consensus aids. 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 forecast, users should be prepared for additional adjustments to the NHC track prediction 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, which is the reason the vortex is currently titled. The shear should persist for another day or so, and little change in strength seems likely during that time period. However, strengthening is expected on Friday and Saturday as the shear decreases while the storm remains over the Gulf Stream. Some weakening seems likely at days 4 and 5 when the storm is expected to be over cooler waters. The NHC intensity forecast lies roughly near the middle of the guidance envelope and only minor changes were made to the previous prediction. Key Messages: 1. The forecast track of Henri has shifted toward the northeast coast of the U.S. this weekend and early next week, increasing the risk of direct storm surge, wind, and rain impacts in portions of the northeastern U.S. and Atlantic Canada during that time. Interests in these areas should closely follow the progress of Henri and check for updates to the forecast. 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 18/2100Z 29.9N 67.6W 60 KT 70 MPH 12H 19/0600Z 29.8N 69.0W 60 KT 70 MPH 24H 19/1800Z 29.8N 70.7W 60 KT 70 MPH 36H 20/0600Z 30.1N 72.3W 65 KT 75 MPH 48H 20/1800Z 31.0N 73.2W 70 KT 80 MPH 60H 21/0600Z 32.7N 72.7W 75 KT 85 MPH 72H 21/1800Z 35.2N 71.7W 80 KT 90 MPH 96H 22/1800Z 39.3N 70.0W 70 KT 80 MPH 120H 23/1800Z 41.4N 69.8W 60 KT 70 MPH $$ Forecaster Cangialosi
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