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Tropical Depression NINE


Tropical Depression Nine Discussion Number   3
NWS National Hurricane Center Miami FL       AL092018
500 AM AST Sat Sep 08 2018

The depression continues to be affected by moderate to strong east
to southeasterly vertical wind shear, which has resulted in the
bulk of the deep convection being displaced to the west of the
low-level center. The initial intensity has been held at 30 kt
based on Dvorak satellite intensity estimate of T2.0/30 kt from
both TAFB and SAB.

The depression has been meandering in the same general area for the
past 12-18 h due to being caught in a weakness in the subtropical
ridge. However, recent microwave satellite data suggest that the
cyclone is now moving slowly northwestward. A turn toward the west
is expected to occur later today as a shortwave trough to the north
that has weakened the ridge lifts out, allowing the ridge to fill
back in and build westward to the north of the Lesser Antilles. The
latest NHC model guidance suite remains tightly packed, and the
official forecast track lies down the middle of the envelope near a
blend of the consensus aids TCVA, HCCA, FSSE.

Although the wind shear is forecast to gradually weaken and become
less than 5 kt by 36-48 h, which would favor rapid strengthening,
the airmass that the cyclone is embedded is fairly dry. Since
mid-level humidity values are forecast to decrease from the current
60-percent range down to around 50 percent by 48 hours and beyond,
only modest strengthening is expected during the next 4 days. By day
5, vertical wind shear from the southwest is forecast to increase to
20-25 kt, serving to cap the intensification process. The NHC
intensity forecast is based on a blend of the IVCN and the HCCA
consensus models, and continues to remain below the stronger HWRF
model at days 4 and 5, which makes the cyclone a major hurricane in
78 h.


INIT  08/0900Z 14.3N  35.4W   30 KT  35 MPH
 12H  08/1800Z 14.4N  36.1W   35 KT  40 MPH
 24H  09/0600Z 14.5N  37.5W   40 KT  45 MPH
 36H  09/1800Z 14.7N  39.5W   45 KT  50 MPH
 48H  10/0600Z 14.6N  42.0W   55 KT  65 MPH
 72H  11/0600Z 14.5N  47.3W   75 KT  85 MPH
 96H  12/0600Z 14.6N  52.7W   80 KT  90 MPH
120H  13/0600Z 14.9N  57.2W   80 KT  90 MPH

Forecaster Stewart