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Tropical Depression Sixteen Forecast Discussion Number 1
2021-09-19 04:31:48| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 18 2021 000 WTNT41 KNHC 190231 TCDAT1 Tropical Depression Sixteen Discussion Number 1 NWS National Hurricane Center Miami FL AL162021 1100 PM AST Sat Sep 18 2021 Satellite images and surface observations indicate that the area of low pressure that NHC has been monitoring to the east of the northern Leeward Islands now has a well-defined center and sufficiently organized deep convection to be classified a tropical depression. The depression has a small area of deep convection near its center and curved bands on its north and east sides. The initial intensity is estimated to be 30 kt, but this is a little below the latest Dvorak classifications and could be conservative. The depression is moving west-northwestward at 12 kt. The cyclone should continue west-northwestward at about the same pace during the next few days as it moves in the flow on the southwest side of a mid-level ridge. After that time, the ridge is expected to break down and the steering currents are forecast to become weak. Not surprisingly, the spread in the models increases around that time, but most of the solutions show a slow turn toward the north toward broad troughing associated with Post-Tropical Cyclone Odette. The GFS is on the southern side of the guidance envelope and the ECMWF on the northern side. The NHC track forecast lies between those models near the consensus aids. Some strengthening seems possible during the next 12 to 24 hours and the system is expected to become a tropical storm during that time frame. However, an increase in southerly and then southwesterly vertical wind shear should cause the system to level off in strength from 24 hours through the end of the forecast period. The models are in fairly good agreement on this overall scenario, and the NHC intensity forecast is in line with the majority of the guidance. Based on the track, intensity, and wind radii forecast, no tropical storm watches or warnings are required for the northern Leeward Islands, Virgin Islands or Puerto Rico. However, interests there should monitor the progress of the system as locally heavy rain is possible on Monday and Tuesday when it is expected to pass to the north of the area. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 16.4N 53.1W 30 KT 35 MPH 12H 19/1200Z 17.3N 54.8W 35 KT 40 MPH 24H 20/0000Z 18.5N 57.3W 40 KT 45 MPH 36H 20/1200Z 19.4N 59.8W 40 KT 45 MPH 48H 21/0000Z 20.3N 61.9W 35 KT 40 MPH 60H 21/1200Z 21.3N 64.1W 35 KT 40 MPH 72H 22/0000Z 22.3N 65.5W 35 KT 40 MPH 96H 23/0000Z 24.4N 66.5W 35 KT 40 MPH 120H 24/0000Z 26.3N 66.2W 35 KT 40 MPH $$ Forecaster Cangialosi
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