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Tropical Storm GABRIELLE


Tropical Storm Gabrielle Discussion Number   7
NWS National Hurricane Center Miami FL       AL082019
500 AM AST Thu Sep 05 2019

METEOSAT imagery and an earlier WindSat microwave overpass show
Gabielle's poorly defined center of circulation sheared well to the
south of the curved convective band features to north, indicative of
moderate southerly shear.  The initial intensity is held at a
generous 45 kt for this advisory, and is based on the subjective
T-numbers from TAFB and SAB.

Although Gabrielle could experience some intensity fluctuations
during the next 24 hours, the cyclone should remain in a
rather harsh environment during the next 36-48 hours, due to
south to southwesterly vertical shear, some dry air in the middle
portions of the atmosphere, and oceanic sea surface temperatures on
the order of 25-26C.  Afterward, gradual strengthening is forecast
as Gabrielle moves into a more favorable upper wind pattern and
warmer SSTs, and this is consistent with the IVCN multi-model
consensus and the Decay SHIPS.

After the adjustment to the south of the previous advisory based
on the ASCAT-A/B scatterometer passes and a recent SSMI/S image, the
initial motion is estimated to be northwestward, or 315/7 kt.  For
the next several days, Gabrielle is expected to move generally
northwestward toward a large weakness in the mid-Atlantic
subtropical ridge.  An increase in forward motion is expected as the
steering flow strengthens between a cut-off low to the west and high
pressure to the northeast.  Around days 4 and 5, the cyclone should
turn generally northward in response to an approaching
mid-tropospheric short wave trough.  An adjustment to the right of
the previous forecast was made, and the NHC forecast is based on a
blend of the various consensus models.


INIT  05/0900Z 21.9N  35.0W   45 KT  50 MPH
 12H  05/1800Z 22.7N  35.8W   45 KT  50 MPH
 24H  06/0600Z 24.2N  37.3W   45 KT  50 MPH
 36H  06/1800Z 26.1N  39.1W   45 KT  50 MPH
 48H  07/0600Z 28.0N  41.0W   45 KT  50 MPH
 72H  08/0600Z 31.6N  46.1W   55 KT  65 MPH
 96H  09/0600Z 35.8N  48.7W   60 KT  70 MPH
120H  10/0600Z 40.6N  44.7W   60 KT  70 MPH

Forecaster Roberts