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Tropical Depression Eight Forecast Discussion Number 2
2021-08-16 10:50:11| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Aug 16 2021 000 WTNT43 KNHC 160850 TCDAT3 Tropical Depression Eight Discussion Number 2 NWS National Hurricane Center Miami FL AL082021 500 AM AST Mon Aug 16 2021 Satellite imagery and radar data from Bermuda indicate that the tropical depression located about 100 nmi east of Bermuda has been moving southward and also remains a sheared tropical cyclone -- the ongoing saga of the Atlantic basin thus far this hurricane season. Convection has increased and developed closer to the center and a late-arriving ASCAT-C overpass indicated surface winds of 26-27 kt to the south of the well-defined circulation center. Based on those data, the slightly improved convective structure noted in both satellite and radar data, and satellite classifications of T2.0/30 kt, the initial intensity has been increased to 30 kt. The initial motion estimate is 195/04 kt. The small cyclone is starting to make the clockwise turn toward the south-southwest and eventually southwest that the global and regional models have been advertising the past couple of days. The latest NHC model guidance now shows less of a turn to the northwest after 72 hours, with the exception of the GFS, GFS-ensemble, and HMON models, which continue to take the cyclone northward and northeastward around Bermuda on day 4 and 5. The latest NHC track forecast is similar to the previous advisory track through 60 hours, and then widens the track slightly thereafter, but still shows a complete clockwise turn. This track scenario is to the right of the consensus models at all forecast periods, and is of low confidence on days 4 and 5. The vertical wind shear is forecast to remain at or below 10 kt for the next 36 hours or so, and that is most likely the time when the cyclone will strengthen. Thereafter, an increase in the shear to 20 kt or more is expected to cap the intensification process. The HWRF model turn the cyclone into a major hurricane by 72 hours, but this scenario is considered to be an extreme outlier given the amount of shear forecast to affect the system on days 3-5. So far this season, the HWRF model has been very shear resistant and has had a high intensity bias. The official intensity forecast closely follows a blend of the IVCN and HCCA consensus models through 60 hours, and then is below those models due to the high-bias contribution of the HWRF model. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 32.4N 62.9W 30 KT 35 MPH 12H 16/1800Z 31.6N 63.1W 35 KT 40 MPH 24H 17/0600Z 31.0N 63.7W 40 KT 45 MPH 36H 17/1800Z 30.7N 64.5W 45 KT 50 MPH 48H 18/0600Z 30.7N 65.5W 50 KT 60 MPH 60H 18/1800Z 30.8N 66.7W 55 KT 65 MPH 72H 19/0600Z 31.1N 68.0W 55 KT 65 MPH 96H 20/0600Z 32.0N 69.0W 55 KT 65 MPH 120H 21/0600Z 34.0N 68.5W 55 KT 65 MPH $$ Forecaster Stewart
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