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| #1057462 (Received by flhurricane at: 11:18 PM 17.Aug.2021) TCDAT3 Tropical Storm Henri Discussion Number 9 NWS National Hurricane Center Miami FL AL082021 1100 PM AST Tue Aug 17 2021 Henri`s appearance on satellite imagery has remained more or less steady-state, featuring a small CDO with additional convective banding along the eastern side of the circulation. However, the earlier mid-level eye feature that was trying to develop on radar from Bermuda has recently become more ill-defined, possibly due to some dry-air being entrained into the inner-core of the storm. The latest Dvorak subjective estimates from SAB and TAFB were T3.0/45 kt and T3.5/55 kt, respectively. In addition, a 2336 UTC ASCAT-A pass had lower peak wind retrievals than what was found earlier today, but this instrument may not be quite able to sample the relatively small tropical cyclone core observed on radar. For now, the initial intensity will be held at 55 kt, though this estimate could be a bit generous given the recent scatterometer data. Henri has begun a more pronounced motion to the west-southwest, and the latest initial motion is estimated at 255/08 kt. An amplified mid- to upper-tropospheric ridge located northwest of Henri is expected to keep the storm on a west-southwestward or westward heading in the short term. However this ridge will begin to gradually erode as an mid- to upper-level trough propagates eastward to the Eastern United States. This should allow Henri to start gaining latitude by 48 hours, turning toward the northwest, north, and then northeast as the mid-level ridging redevelops southeast of the cyclone. There remains a large amount of spread in the guidance, with the stronger regional hurricane models on the left side, while the weaker global models remain more on the right side of the guidance envelope. In general though, there was another westward shift in the guidance suite, so the latest NHC forecast track was adjusted again in that direction, and is in closest agreement to the HCCA guidance aid. The intensity forecast in the short-term is tricky. Last night and this morning, Henri`s deep convection was been able to propagate into its up-shear quadrant, in spite of light to moderate northwesterly shear importing fairly dry mid-latitude air from the north. Consequently, the storm has been able to intensify and become more axis-symmetrical. Over the past few hours, however, the convection to the northwest of the center has eroded once again on Bermuda radar, likely due to dry air entrainment by the aforementioned vertical wind shear. On the other hand, the tropical cyclone is currently over sea-surface temperatures above 29 C, which will likely allow for significant boundary layer recovery of dry mid-level air that is able to get into the inner core. Thus, even as northerly vertical wind shear increases over the next 24 hours, Henri is expected to maintain its intensity. After 60 hours, this northerly shear is expected to subside, and Henri will have an opportunity to intensify towards the end of the forecast. The latest NHC intensity forecast is quite similar to the previous one for the first 60 hours, but is a little stronger in the latter time periods, blending the reliable HCCA guidance with the more aggressive regional hurricane models (HWRF, COAMPS-TC). FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 30.0N 65.1W 55 KT 65 MPH 12H 18/1200Z 29.9N 66.0W 60 KT 70 MPH 24H 19/0000Z 29.8N 67.7W 60 KT 70 MPH 36H 19/1200Z 29.8N 69.5W 60 KT 70 MPH 48H 20/0000Z 30.1N 71.1W 60 KT 70 MPH 60H 20/1200Z 30.9N 72.0W 60 KT 70 MPH 72H 21/0000Z 32.0N 71.9W 70 KT 80 MPH 96H 22/0000Z 36.6N 69.4W 80 KT 90 MPH 120H 23/0000Z 40.2N 65.0W 80 KT 90 MPH $$ Forecaster Papin/Brown |
