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Tropical Storm Henri Forecast Discussion Number 6
2021-08-17 10:31:26| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Aug 17 2021 790 WTNT43 KNHC 170831 TCDAT3 Tropical Storm Henri Discussion Number 6 NWS National Hurricane Center Miami FL AL082021 500 AM AST Tue Aug 17 2021 Earlier this evening Henri was undergoing a sheared bursting pattern, with intermittent deep convection trying to develop near the center, but northwesterly shear would quickly diminish the convective coverage. However, over the past several hours the convection has become more persistent, and covers at least the southeastern portion of the low-level center. As such, the latest subjective Dvorak intensity estimates from TAFB and SAB are now both 3.0 (45 kt), and therefore 45 kt will be the initial advisory intensity. Henri is forecast to remain over warm waters and in an environment of light to moderate northerly shear for the next 24 h, so some strengthening is expected during that time. After 24 h, global models indicate that the shear magnitude will double, which should prevent any further strengthening and possibly weaken the cyclone. The latest NHC intensity forecast was adjusted a little higher than the previous due to both the increase in initial intensity, and slight increase in the model intensity guidance. This forecast closely follows the LGEM solution and is just a little lower than the IVCN consensus. The tropical storm continues to move slowly southwest, or 240/04 kt to the southeast of a mid-level ridge. This ridge is forecast to shift to the east over the next several days, which would result in the tropical storm making a gradual clockwise turn throughout much of the forecast period. Tonight, Henri is forecast to turn westward with a increase in forward motion and pass well south of Bermuda. In a few days, the cyclone should turn to the northwest then north, followed by a turn to the northeast around the western periphery of the ridge. There continues to be some spread in how far west Henri will go before it begins to turn to the north, and the latest guidance has made a slight shift to the left. The official NHC forecast is near the previous one through 48 h, then is a little left of it thereafter, yet still remains to the right of the bulk of the consensus guidance beyond 48 h. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 30.6N 63.7W 45 KT 50 MPH 12H 17/1800Z 30.4N 64.4W 50 KT 60 MPH 24H 18/0600Z 30.3N 65.7W 55 KT 65 MPH 36H 18/1800Z 30.2N 67.1W 55 KT 65 MPH 48H 19/0600Z 30.3N 68.6W 55 KT 65 MPH 60H 19/1800Z 30.8N 69.8W 55 KT 65 MPH 72H 20/0600Z 31.6N 70.6W 55 KT 65 MPH 96H 21/0600Z 34.0N 69.1W 55 KT 65 MPH 120H 22/0600Z 36.0N 66.0W 55 KT 65 MPH $$ Forecaster Latto
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