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Tropical Depression Nine Forecast Discussion


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724 
WTNT42 KNHC 072044
TCDAT2

Tropical Depression Nine Discussion Number   1
NWS National Hurricane Center Miami FL       AL092018
500 PM AST Fri Sep 07 2018

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