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TROPICAL STORM IVETTE DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102016
800 PM PDT WED AUG 03 2016

Moderate northeasterly vertical shear continues to afflict
Ivette, as the deep convection is asymmetric with most of the cold
cloud tops southwest of the center.  A blend of the TAFB and SAB
subjective Dvorak, the CIMSS Advanced Dvorak, and AMSU estimates
gives an intensity of 40 kt, unchanged from the previous advisory.
A pair of ASCAT scatterometer passes around 18Z indicates that
Ivette remains small sized, but slightly larger in
tropical-storm-force wind radii than previously estimated.

The scatterometer passes and an AMSR2 image at 2023Z suggested that
Ivette's center was farther south than previously analyzed.  This
was confirmed by the brief appearance of the low-level center in
geostationary visible imagery, as it peeked out from the edge of the
deep convection.  Ivette is moving toward the west at 14 kt, along
the southern edge of a deep-layer subtropical ridge extending
westward from Mexico.  The tropical cyclone should continue moving
toward the west or west-northwest at a slightly slower rate of
forward speed for the next few days.  The NHC track forecast is
based upon the tightly clustered global and regional hurricane
models, and is slightly south of the previous advisory because of
the southward revision to the initial position.

The continuing steady state of Ivette would argue for little
change in the short term, but the global models insist that the
vertical shear should be diminishing now.  The NHC intensity
forecast assumes that the shear will lower during the next two to
three days while the SSTs are quite warm and the atmosphere is
moist and unstable, leading to a steady intensification of Ivette.
Beyond day three, the vertical shear should ramp up again out of the
southwest as a large upper-level trough approaches Ivette while the
SSTs cool, causing Ivette to gradually weaken.  The NHC intensity
forecast is based upon a blend of the SHIPS and HWRF models, and is
slightly below that from the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 14.6N 123.4W   40 KT  45 MPH
 12H  04/1200Z 14.7N 125.5W   45 KT  50 MPH
 24H  05/0000Z 14.9N 128.2W   50 KT  60 MPH
 36H  05/1200Z 15.1N 130.5W   60 KT  70 MPH
 48H  06/0000Z 15.5N 132.5W   70 KT  80 MPH
 72H  07/0000Z 16.7N 136.3W   75 KT  85 MPH
 96H  08/0000Z 18.0N 140.0W   65 KT  75 MPH
120H  09/0000Z 19.0N 143.0W   50 KT  60 MPH

$$
Forecaster Landsea

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