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TROPICAL STORM IVETTE DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102016
200 AM PDT FRI AUG 05 2016

There has been little change in the convective organization of
Ivette overnight.  The low-level center remains exposed to the
west and northwest of a loosely curved band of thunderstorms, due
to westerly to northwesterly shear.  Subjective and objective
Dvorak T-numbers are all near T3.0, which yields an initial
wind speed of 45 kt.  Although the shear is not very strong, it
appears the small size of the cyclone and perhaps some nearby dry
mid-level air in combination with the shear have prevented
intensification during the past day.  The GFS-based SHIPS guidance
indicates that the shear will decrease during the next 24 hours or
so, but the ECMWF model shows a continuation of some upper-level
westerlies over Ivette.  Because of these differences in the
expected upper-level winds, the NHC intensity forecast is more
uncertain than normal.  The updated intensity forecast calls for
some slight strengthening during the next 36 hours, but it is lower
than the previous advisory, and it is closest to the IVCN intensity
consensus.  After 48 h, increasing southwesterly shear and cooler
SSTs should cause a fairly rapid spin down of Ivette, and the
cyclone is likely to become a remnant low in 4 to 5 days.

The tropical storm is moving westward or 275/12 kt.  Ivette should
turn west-northwestward in 12 to 24 hours as a deepening mid- to
upper-level trough to the north of the Hawaiian Islands weakens the
western portion of the subtropical ridge.  After day 3, Ivette is
forecast to turn back westward after it weakens and is steered by
the low-level easterly trades.  There remains high confidence in the
track forecast since the dynamical models continue to be in good
agreement.

FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 14.9N 129.7W   45 KT  50 MPH
 12H  05/1800Z 15.2N 131.2W   45 KT  50 MPH
 24H  06/0600Z 15.8N 133.1W   50 KT  60 MPH
 36H  06/1800Z 16.4N 134.8W   55 KT  65 MPH
 48H  07/0600Z 17.2N 136.5W   55 KT  65 MPH
 72H  08/0600Z 18.5N 139.5W   40 KT  45 MPH
 96H  09/0600Z 19.0N 142.7W   30 KT  35 MPH
120H  10/0600Z 18.8N 146.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown

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