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Tropical Storm Henri Forecast Discussion Number 4
2021-08-16 22:46:40| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Aug 16 2021 000 WTNT43 KNHC 162046 TCDAT3 Tropical Storm Henri Discussion Number 4 NWS National Hurricane Center Miami FL AL082021 500 PM AST Mon Aug 16 2021 Deep convection has persisted near and southeast of the center of the small tropical cyclone today, and subjective Dvorak intensity estimates were a consensus T2.5 (35 kt) at 1800 UTC. Objective estimates from ADT and SATCON also support tropical storm status, therefore the depression has been upgraded to a 35-kt tropical storm with this advisory. Henri (ahn-REE) becomes the eighth named storm of the 2021 Atlantic hurricane season. This is the fourth-earliest eighth storm on record with only 2020, 2005, and 1936 having the eighth-named storm form earlier in the season. Henri is located over warm waters, but is currently being affected by light to moderate northerly shear and dry mid-level air in the surrounding environment. Although these conditions are not overly conducive for strengthening, most of the intensity guidance supports gradual intensification over the next 24 to 48 hours. After that time, a significant increase in northeasterly upper-level winds is depicted by the global models over the system, which is likely to halt further strengthening. In fact, given the small size of Henri, it is likely to be more susceptible to the increase in shear, and it could weaken faster than indicated below. The HWRF remains more aggressive, but given the expected increase in shear, that solution still does not seem likely. The NHC intensity forecast is in best agreement with the LGEM model, and is slightly below the IVCN intensity consensus. The tropical storm is moving south-southwestward or 200/6 kt. Henri is forecast to move west-southwestward during the next 12-24 hours around the southeastern side of a mid-tropospheric high over the western Atlantic. After that time, Henri should turn westward as the ridge shifts eastward to the north of the tropical cyclone, and after 72 hours Henri is expected to approach the western extent of the ridge and should turn northward and then north-northeastward. The dynamical model guidance is in somewhat better agreement during the next 48-72 hours, but there remains some spread later in the period as to how sharp of northward turn occurs. The new NHC track forecast is similar to the previous advisory and lies near the center of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 31.0N 62.9W 35 KT 40 MPH 12H 17/0600Z 30.5N 63.4W 40 KT 45 MPH 24H 17/1800Z 30.3N 64.2W 45 KT 50 MPH 36H 18/0600Z 30.2N 65.4W 50 KT 60 MPH 48H 18/1800Z 30.2N 66.9W 50 KT 60 MPH 60H 19/0600Z 30.3N 68.5W 50 KT 60 MPH 72H 19/1800Z 30.5N 69.9W 45 KT 50 MPH 96H 20/1800Z 31.8N 70.2W 45 KT 50 MPH 120H 21/1800Z 34.2N 68.4W 45 KT 50 MPH $$ Forecaster Brown
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