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TROPICAL STORM IVETTE DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102016
200 PM PDT FRI AUG 05 2016

Visible and microwave satellite imagery indicate that deep-layer
westerly shear continues to affect Ivette.  However, water vapor
imagery does show cirrus expanding westward, so the shear is most
likely confined to the layer below the outflow level.  Nonetheless,
Dvorak intensity estimates from TAFB and SAB are T3.0/45 kt and
T3.5/55 kt, respectively, and the UW-CIMSS ADT is up to T5.3/53 kt.
Based on these data, the initial intensity is raised to 50 kt.

The initial motion is 280/11 kt.  Ivette is located due south of a
mid-level anticyclone, which is causing the cyclone's westward
motion.  Ivette will soon be reaching the western edge of the
anticyclone, causing it to turn west-northwestward and slow down
soon while it approaches a mid- to upper-level trough northeast of
Hawaii.  After day 3, the remnant low associated with Ivette should
turn westward, steered by the low-level trades.  Although the ECMWF
is somewhat faster and farther south than the other models, there
is still very little spread among the guidance.  The NHC track
forecast is just a little south of the multi-model consensus and
not too different from the previous forecast.

Vertical shear is probably not going to decrease, and, in fact, it
should increase to over 20 kt in about 36 hours, lasting through the
rest of the 5-day period.  Ivette does appear that it will reach
warmer waters (around 29C) in about 24 hours, which could foster
just a little more strengthening.  After that time, however, the
hostile shear should cause a fast weakening trend, and Ivette is
likely to become a remnant low by day 4.  The global models seem to
suggest that the remnant low could degenerate into a trough by day
5, but for now the official forecast will carry a low through the
end of the forecast period.  The NHC intensity forecast is very
close to the IVCN consensus and not too different from the previous
forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 15.5N 131.8W   50 KT  60 MPH
 12H  06/0600Z 15.9N 133.2W   55 KT  65 MPH
 24H  06/1800Z 16.6N 135.1W   55 KT  65 MPH
 36H  07/0600Z 17.2N 136.8W   50 KT  60 MPH
 48H  07/1800Z 17.9N 138.6W   45 KT  50 MPH
 72H  08/1800Z 18.8N 141.6W   35 KT  40 MPH
 96H  09/1800Z 18.5N 145.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  10/1800Z 18.0N 150.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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