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TROPICAL STORM BLAS DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP032016
900 AM MDT SUN JUL 03 2016

Satellite imagery indicates a marked increase in organization of the
Blas' cloud pattern overnight, suggesting that the cyclone is
quickly intensifying.  The center is located underneath a ball of
deep convection, the latter which appears to be a formative central
dense overcast.  The large-envelope cyclone also has a lengthening
band that consists of very cold-topped convection in the shape of a
figure six. Satellite classifications are T3.0/45 kt and T3.5/55 kt
from SAB and TAFB at 1200 UTC, respectively.  The initial intensity
is raised to 50 kt, based on a blend of the two intensity estimates.

The initial motion estimate is 285/11.  Blas is forecast to move
along the southern periphery of a deep-layer subtropical ridge
centered over northern Mexico throughout the forecast period, which
should keep the cyclone on a general west-northwesterly course.  The
model guidance is in very good agreement through 72 hours, but
diverges after that time.  The GFS and its ensemble mean lie near
the previous forecast and is on the northern side of the guidance
envelope, while the ECMWF and its ensemble mean are much farther
south.  The differences between the two models appear related to
subtle variations in the strength and position of the subtropical
ridge forecast after day 3.  The NHC track forecast is adjusted a
bit south of the previous one, on the southern side of the guidance
envelope through 72 hours and near the multi-model consensus after
that time.

There does not appear to be anything obvious on the large-scale to
impede intensification over the next few days, except that the
cyclone will be very gradually departing the warmest waters over the
basin.  The light-easterly-shear, moist environment and warm waters
should allow Blas to strengthen into a major hurricane as indicated
in about 48 hours.  The official NHC forecast through that time is
heavily weighted toward the statistical guidance which is performing
well, considering the current developmental trend.  By 96 hours,
even though the shear is forecast to remain low, the cyclone should
be moving over steadily cooler waters and entering a drier and more
stable environment.  This should foster a weakening trend, though
the weakening will likely occur only gradually.

FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 11.6N 110.3W   50 KT  60 MPH
 12H  04/0000Z 12.1N 112.0W   60 KT  70 MPH
 24H  04/1200Z 12.6N 114.1W   75 KT  85 MPH
 36H  05/0000Z 13.1N 116.4W   90 KT 105 MPH
 48H  05/1200Z 13.6N 118.7W  100 KT 115 MPH
 72H  06/1200Z 14.6N 123.3W  105 KT 120 MPH
 96H  07/1200Z 16.0N 127.7W   95 KT 110 MPH
120H  08/1200Z 17.3N 131.3W   85 KT 100 MPH

$$
Forecaster Kimberlain

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