000
WTNT42 KNHC 231435
TCDAT2

TROPICAL STORM GASTON DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016
1100 AM AST TUE AUG 23 2016

Gaston continues to intensify.  The cyclone's cloud pattern has been
gradually transitioning from a curved-band pattern to a central
dense overcast (CDO).  Within the formative CDO, a ragged eye-type
feature has occasionally been evident during the last few hours.  A
satellite classification of T3.5 is used to increase in the initial
intensity estimate to 55 kt, in agreement with the latest UW-CIMSS
ADT values.

Only light vertical wind shear is forecast to affect Gaston during
the next 24 to 36 hours while the cyclone moves over marginally
warm waters and through a generally moist environment.  These
factors suggest that further intensification is likely during this
period of time.  By 48 hours, Gaston should encounter increasing
southwesterly to westerly flow at upper-levels associated with a
potent trough over the east-central Atlantic.  In the very least,
the forecast shear and a drier atmosphere associated with this
feature should result in an arrested development phase, if not
weakening.  Late in the forecast period, global models indicate a
reduction of the shear while Gaston is over warmer waters of 29 deg
C, which could allow for some re-strengthening.  Through 36 hours,
the NHC intensity forecast is a bit above the multi-model consensus
and closest to the FSU Superensemble output and the LGEM. After that
time, the forecast trends toward the multi-model consensus.

The initial motion estimate is 285/18.  Gaston is being steered
quickly toward the west-northwest around the western extension of
a mid-level subtropical ridge extending westward from North Africa.
The ridge's orientation begins to change as Gaston approaches a
significant break in the subtropical ridge in the central Atlantic,
which results in a northwestward heading and a reduction in
forward speed during the next few days.  A northward turn with an
even greater decrease in forward speed is expected by 120 hours
once Gaston enters the weakness over the central Atlantic.  The
latest NHC track forecast is largely similar to the previous one
and close to the model consensus aids.




FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 13.8N  34.6W   55 KT  65 MPH
 12H  24/0000Z 14.6N  36.9W   65 KT  75 MPH
 24H  24/1200Z 16.1N  39.9W   75 KT  85 MPH
 36H  25/0000Z 17.8N  42.4W   85 KT 100 MPH
 48H  25/1200Z 19.8N  44.6W   80 KT  90 MPH
 72H  26/1200Z 24.2N  48.9W   75 KT  85 MPH
 96H  27/1200Z 27.7N  52.5W   75 KT  85 MPH
120H  28/1200Z 30.7N  53.5W   80 KT  90 MPH

$$
Forecaster Kimberlain