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Tropical Depression TEN Forecast Discussion Number 1
2015-09-18 16:32:27| National Hurricane Center (Atlantic)
Issued at 1100 AM AST FRI SEP 18 2015 000 WTNT45 KNHC 181432 TCDAT5 TROPICAL DEPRESSION TEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 1100 AM AST FRI SEP 18 2015 Satellite data indicate that the area of low pressure over the tropical eastern Atlantic has acquired sufficient organization to be classified as a tropical depression. The low-level center appears embedded beneath a relatively small cluster of deep convection, but convective banding is also increasing to the west and north. The initial intensity is set at 25 kt based on Dvorak estimates from TAFB and SAB and recent ASCAT data. The depression is located near the southwestern edge of a mid-level anticyclone, giving the cyclone an initial motion of 285/8 kt. The anticyclone is expected to move westward in tandem with the depression over the next couple of days, keeping it on a general west-northwestward track for much of the forecast period. By days 4 and 5, however, there is significant uncertainty in the track forecast. The GFS and GFDL show the cyclone feeling the influence of an amplifying deep-layer trough over the eastern Atlantic, which turns the depression northward. The ECMWF and UKMET, on the other hand, keep the ridge as the dominant influence and continue a west-northwestward motion. Due to the large spread in the guidance, the official forecast shows the cyclone slowing down considerably by days 4 and 5, and is a little west of the model consensus aids at those times. The environment looks conducive for at least gradual strengthening during the forecast period. Sea surface temperatures are warm, vertical shear should remain generally low, and environmental moisture patterns appear favorable for at least the next two days. Beyond 48 hours, most of the global models show the cyclone threading the needle beneath a narrow upper-level ridge, with mid-level dry air possibly getting into the western part of the cyclone's circulation. This pattern makes the intensity forecast complicated because hostile upper-level winds won't be too far away, and the ultimate strength of the cyclone will depend heavily on its eventual track. For now, the NHC official forecast shows only gradual strengthening through day 4, more or less in line with the SHIPS and LGEM guidance. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 13.1N 36.7W 25 KT 30 MPH 12H 19/0000Z 13.4N 37.6W 30 KT 35 MPH 24H 19/1200Z 14.2N 39.0W 30 KT 35 MPH 36H 20/0000Z 15.2N 40.8W 35 KT 40 MPH 48H 20/1200Z 16.4N 43.0W 40 KT 45 MPH 72H 21/1200Z 18.3N 46.4W 45 KT 50 MPH 96H 22/1200Z 19.5N 48.0W 50 KT 60 MPH 120H 23/1200Z 20.0N 49.0W 50 KT 60 MPH $$ Forecaster Berg
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