ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST THU SEP 15 2016 Visible satellite images indicate that the depression has a rather impressive low-level circulation, although all the deep convection is far removed from the center due to southwesterly shear. Given such a well-defined circulation, the depression could have become a tropical storm overnight. The initial wind speed, however, remains 30 kt using a blend of the TAFB/SAB estimates with any of the more reliable ASCAT passes unfortunately missing the center during the past 18 hours. An upper-level trough to the northwest of the cyclone is expected to cause an increase in shear during the next day or so, which will likely cause the cyclone to weaken. Beyond 48 hours, most of the models show the shear relaxing, with an upper-level high taking the place of the trough, and the cyclone is forecast to move over warmer waters. This will probably promote a restrengthening trend, although guidance is in poor agreement on how much the winds could increase. Thus, the official forecast is reduced a little bit for Friday/Saturday due to the shear, then is the same as the previous one, showing a slow restrengthening early next week. It is also possible the cyclone will degenerate into a remnant low for a while due to the shear, although this isn't the likeliest scenario. The depression is moving westward at about 11 kt, and this general motion should continue for a day or so while it moves around the Atlantic subtropical ridge. This ridge is forecast by much of the guidance to strengthen and build westward, which would force the depression to the west-southwest over the weekend. Early next week, the cyclone could begin to gain some latitude as it reaches the southwestern periphery of the ridge. Guidance is in good agreement on this scenario, except for the GFDL which appears to be a northward outlier. The official forecast track is very close to a blend of the other models in the TVCN consensus minus the GFDL, and is basically an update of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 17.7N 30.4W 30 KT 35 MPH 12H 16/0000Z 17.8N 32.2W 30 KT 35 MPH 24H 16/1200Z 17.9N 34.8W 30 KT 35 MPH 36H 17/0000Z 17.7N 37.4W 25 KT 30 MPH 48H 17/1200Z 17.4N 40.1W 25 KT 30 MPH 72H 18/1200Z 16.5N 45.2W 30 KT 35 MPH 96H 19/1200Z 16.7N 50.3W 35 KT 40 MPH 120H 20/1200Z 17.5N 55.0W 40 KT 45 MPH $$ Forecaster Blake NNNN
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Page last modified: Saturday, 31-Dec-2016 12:09:36 UTC