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Tropical Depression Nine Forecast Discussion Number 1
2018-09-07 22:58:58| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Sep 07 2018 888 WTNT44 KNHC 072058 CCA TCDAT4 Tropical Depression Nine Discussion Number 1...Corrected NWS National Hurricane Center Miami FL AL092018 500 PM AST Fri Sep 07 2018 Corrected bin number from 2 to 4 Satellite images indicate that the low pressure system over the eastern tropical Atlantic has developed a well-defined center and sufficient deep convection to be classified a tropical depression, the ninth one of the 2018 Atlantic hurricane season and second one of the day. The initial intensity is set to 30 kt based on a 2.0 Dvorak classification from TAFB and earlier ASCAT data. The depression has not moved much today, and it has even wobbled a bit to the east recently. This slow motion is a result of very weak steering with broad troughing to the north and Tropical Depression Eight to its east. Little motion is expected through tonight, but a westward motion with a gradual increase in forward speed is forecast thereafter as a subtropical ridge builds to the north of the cyclone. The NHC track forecast lies closest to the HCCA guidance and takes the system toward the Lesser Antilles by the end of the forecast period. The depression is experiencing some influences of easterly shear, which is why the center is currently on the eastern edge of the convection. Little change in intensity is expected during the next 12 to 24 hours since the cyclone is still in the developing stage and because moderate shear is expected to continue. However, the shear is expected to decrease to less than 10 kt in about 24 hours. These more favorable winds aloft combined with relatively warm waters and a fairly moist airmass should allow for steady strengthening beginning later in the weekend. There is a large spread in the intensity guidance, with the HWRF showing the system becoming a major hurricane and HMON showing almost no strengthening. The NHC intensity forecast lies a little below consensus models since it appears that it will take some time for the system to strengthen. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 13.6N 34.9W 30 KT 35 MPH 12H 08/0600Z 13.9N 35.2W 30 KT 35 MPH 24H 08/1800Z 14.0N 36.2W 30 KT 35 MPH 36H 09/0600Z 14.0N 37.6W 40 KT 45 MPH 48H 09/1800Z 14.0N 39.3W 50 KT 60 MPH 72H 10/1800Z 14.0N 44.0W 60 KT 70 MPH 96H 11/1800Z 14.1N 48.9W 70 KT 80 MPH 120H 12/1800Z 14.5N 54.5W 75 KT 85 MPH $$ Forecaster Cangialosi
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