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TROPICAL STORM GASTON DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016
500 PM AST TUE AUG 23 2016

The cloud pattern of Gaston has not changed much during the past
several hours, although perhaps the convection has become more
symmetric.  Satellite classifications are about the same as before,
so the initial wind speed remains 55 kt.  Gaston has about 24-36
hours to intensify before southwesterly vertical wind shear
associated with a mid-tropospheric trough is forecast to increase.
This shear should result in some weakening of the cyclone in the
2 or 3 day time frame. Thereafter, Gaston moves away from the
trough, and since the cyclone should be over warm waters near 29C,
some restrengthing is likely.  Considering the complexity of the
scenario, the guidance is in relatively good agreement on this
pattern.  The official forecast follows the trend of the previous
forecast and the intensity consensus.

The initial motion estimate is 290/16.  Gaston should gradually turn
northwestward during the next couple of days as it moves around the
subtropical ridge.  Guidance is in very good agreement on the
forecast during that time, and little change is made to the
previous NHC track in the shorter term.  Beyond 3 days, a break in
the subtropical ridge is forecast, although the models are not in
great agreement on exactly what longitude Gaston reaches before its
likely recurvature.  Overall, the model guidance has shifted a bit
westward, and the latest NHC track forecast is shifted in that
direction.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 14.2N  35.8W   55 KT  65 MPH
 12H  24/0600Z 15.2N  38.1W   65 KT  75 MPH
 24H  24/1800Z 16.8N  40.7W   75 KT  85 MPH
 36H  25/0600Z 18.7N  43.2W   80 KT  90 MPH
 48H  25/1800Z 20.8N  45.4W   80 KT  90 MPH
 72H  26/1800Z 25.5N  49.6W   70 KT  80 MPH
 96H  27/1800Z 28.5N  53.5W   75 KT  85 MPH
120H  28/1800Z 31.0N  54.5W   85 KT 100 MPH

$$
Forecaster Blake

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