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Tropical Depression SIX Forecast Discussion Number 1
2016-08-17 04:48:08| National Hurricane Center (Atlantic)
Issued at 1100 PM AST TUE AUG 16 2016 000 WTNT41 KNHC 170248 TCDAT1 TROPICAL DEPRESSION SIX DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST TUE AUG 16 2016 Convective activity associated with the tropical wave and associated low pressure area over the tropical Atlantic has become more concentrated and better organized this evening, and a recent ASCAT overpass indicates that the circulation has become better defined. Based on these data, this system has been designated a tropical depression, and advisories are being initiated at this time. The initial wind speed of 30 kt is supported by the scatterometer data. Some northeasterly shear is affecting the depression, with the center located near the northeastern edge of the primary convective mass. The shear is forecast to decrease tonight and remain low during the next couple of days which favors strengthening. However, dry mid-level air is lurking just to the north of the depression, and intrusions of this unfavorable airmass could arrest development. The NHC forecast shows gradual strengthening during the next couple of days, but it is on the lower side of the guidance, closest to the LGEM and intensity consensus. Later in the forecast period, increasing southwesterly shear being produced by a mid- to upper-level trough over the central Atlantic is likely to weaken the tropical cyclone. The initial motion estimate is a somewhat uncertain 310/12 kt. The depression is forecast to move generally northwestward into a weakness in the subtropical ridge over the central Atlantic. The track guidance is in relatively good agreement through 48 hours, but there is a large spread between the GFS-based guidance and the ECMWF later in the period. The ECMWF and the majority of its ensemble members depict a much weaker and shallower cyclone that turns west-northwestward in the low-level flow after 48 hours. On the other hand, the GFS, GFS ensemble mean, GFDL, and HWRF take a stronger cyclone more poleward. For now, the NHC track is between these two distinct solutions, and is located just south of the multi-model consensus at days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 12.6N 34.1W 30 KT 35 MPH 12H 17/1200Z 13.7N 35.6W 35 KT 40 MPH 24H 18/0000Z 15.2N 37.2W 40 KT 45 MPH 36H 18/1200Z 16.8N 38.8W 45 KT 50 MPH 48H 19/0000Z 18.1N 40.2W 50 KT 60 MPH 72H 20/0000Z 20.0N 43.2W 50 KT 60 MPH 96H 21/0000Z 22.5N 46.5W 45 KT 50 MPH 120H 22/0000Z 25.0N 50.0W 40 KT 45 MPH $$ Forecaster Brown
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