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413 WTNT43 KNHC 072046 TCDAT3 Tropical Depression Eight Discussion Number 2 NWS National Hurricane Center Miami FL AL082018 500 PM AST Fri Sep 07 2018 Satellite data and surface observations indicate that the low pressure system located just west of the coast of Africa has developed into a tropical depression. Conventional satellite imagery shows a well-defined convective band has formed near the center, and microwave satellite imagery has hinted at the formation of an inner ring of convection. The initial intensity of 30 kt and the central pressure of 1002 mb are based on surface observations from ships and the west coast of Africa. The depression currently has good cirrus outflow in all directions. The initial motion is 275/9. During the next 3-4 days, the cyclone should move generally west-northwestward with an increase in forward speed on the south side of the subtropical ridge over the eastern Atlantic. Near the end of the forecast period, a developing mid- to upper-level trough over the central Atlantic is expected to weaken the ridge and allow the cyclone to turn northwestward with a decrease in forward speed. There is some spread in the guidance late in the period, with the UKMET and the Canadian models showing an earlier turn than the other models. The new forecast track, which is similar to the previous track, is in best agreement with the TVCN and HCCA consensus models. The depression is in an environment of light to moderate easterly vertical shear and over sea surface temperatures of 27-28C. This should allow at least steady strengthening, and rapid strengthening is possible based on the hints of the inner core in microwave imagery. This portion of the intensity forecast has been increased to the upper edge of the intensity guidance, with the cyclone forecast to become a tropical storm in 12 h or less and a hurricane between 48-72 h. After 72 h, the system should be over sea surface temperatures near 26C and encountering southwesterly vertical shear due to the aforementioned trough. This should cause at least a gradual weakening. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 13.2N 18.6W 30 KT 35 MPH 12H 08/0600Z 13.5N 19.9W 35 KT 40 MPH 24H 08/1800Z 13.9N 21.9W 45 KT 50 MPH 36H 09/0600Z 14.4N 24.5W 55 KT 65 MPH 48H 09/1800Z 14.9N 27.5W 60 KT 70 MPH 72H 10/1800Z 16.5N 33.5W 70 KT 80 MPH 96H 11/1800Z 18.0N 38.5W 65 KT 75 MPH 120H 12/1800Z 20.5N 42.0W 60 KT 70 MPH $$ Forecaster Beven