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Tropical Depression ELEVEN Forecast Discussion Number 1
2015-09-28 04:40:02| National Hurricane Center (Atlantic)
Issued at 1100 PM AST SUN SEP 27 2015 000 WTNT41 KNHC 280239 TCDAT1 TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 1100 PM AST SUN SEP 27 2015 Late-afternoon visible satellite imagery indicates that the circulation of the low pressure area located midway between the Bahamas and Bermuda has become well defined. Since the low has already had persistent and organized deep convection, the system is being declared a tropical depression. A 2312 UTC SSMI/S overpass indicated that the center of the depression has become at least partially exposed to the northwest of a large convective mass due to moderate northwesterly shear. The initial wind speed is set to 30 kt, based on a T2.0/30 kt classification from TAFB. The depression is expected to be blasted by strong north-northwesterly or northerly winds associated with the tail of an upper-level trough over the central Atlantic beginning on Monday. In fact, global models show the shear being sufficiently strong enough to result in the cyclone either becoming a remnant low or dissipating within a few days. The intensity forecast is below the multi-model consensus through the forecast period, closest to the HWRF solution. A low- to mid- level ridge north and northeast of the cyclone is steering the lower half of the depression's circulation northwestward while increasing northwesterly winds aloft are opposing this motion. The net deep-layer mean flow is therefore providing for only a slow northwestward motion of 315/02 kt, a rather uncertain estimate considering the scatter of recent fixes. This synoptic pattern is expected to persist for the next couple of days, resulting in a the cyclone's drifting west-northwestward or northwestward. The low- to mid-level ridge is forecast to shift eastward in 2-3 days as a trough reaches the eastern seaboard of the United States, and the increasingly shallow system should turn northwestward and north-northwestward at a faster forward speed if it still exists. The track forecast is close to a blend of the GFS and ECMWF model solutions. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 27.5N 68.7W 30 KT 35 MPH 12H 28/1200Z 27.7N 69.4W 30 KT 35 MPH 24H 29/0000Z 27.9N 69.9W 30 KT 35 MPH 36H 29/1200Z 28.2N 70.4W 30 KT 35 MPH 48H 30/0000Z 28.8N 70.8W 30 KT 35 MPH 72H 01/0000Z 31.0N 71.6W 30 KT 35 MPH 96H 02/0000Z...DISSIPATED $$ Forecaster Kimberlain
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