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TROPICAL STORM IVETTE DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102016
800 AM PDT WED AUG 03 2016

Ivette's convective pattern is gradually improving, with a band
lying to the west of a central cluster of deep convection.
However, recent microwave data still shows the low-level center
displaced to the northeast of the deepest convection due to some
shear.  Dvorak intensity estimates are T3.0/45 kt from SAB and
T2.5/35 kt from TAFB; the initial intensity is therefore raised to
40 kt.

Sea surface temperatures are expected to be 27-28C for the next
96 hours, while the vertical shear affecting the cyclone is
forecast to gradually diminish over the next couple of days.  These
conditions would seem to support steady or even fast strengthening.
Surprisingly, the SHIPS, LGEM, GFDL, and HWRF models only intensify
Ivette to near the hurricane threshold.  Given the seemingly
favorable environment, the NHC official forecast is above all of the
main intensity models, with the exception of COAMPS-TC, and it does
not deviate from the peak intensity indicated in the previous
advisory.  Slightly lower SSTs and increasing shear are likely to
cause some weakening by days 4 and 5.

A strong subtropical ridge extending westward from northern Mexico
is causing Ivette to move quickly west-northwestward at 285/15 kt.
The ridge is expected to remain entrenched north of Ivette for the
next three days, putting the cyclone on a westward heading but with
a gradually decreasing forward speed.  By days 4 and 5, Ivette
could gain a little more latitude due to a break in the ridge that
will develop northeast of the Hawaiian Islands.  There is high
confidence in the future track of Ivette due to a tightly clustered
model envelope, and the NHC track forecast is mainly an update of
the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 14.6N 120.4W   40 KT  45 MPH
 12H  04/0000Z 15.0N 122.7W   45 KT  50 MPH
 24H  04/1200Z 15.2N 125.6W   55 KT  65 MPH
 36H  05/0000Z 15.4N 128.3W   65 KT  75 MPH
 48H  05/1200Z 15.6N 130.8W   70 KT  80 MPH
 72H  06/1200Z 16.5N 135.1W   80 KT  90 MPH
 96H  07/1200Z 18.0N 138.5W   75 KT  85 MPH
120H  08/1200Z 19.0N 141.5W   65 KT  75 MPH

$$
Forecaster Berg

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