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Tropical Depression EIGHT


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.


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