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TROPICAL STORM IGNACIO DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP122015
800 PM PDT TUE AUG 25 2015

Conventional satellite imagery and the latest UW-CIMSS shear
analysis indicates that the southeasterly shear has diminished this
evening.  Subsequently, Ignacio had quickly become better organized
this evening with a small Central Dense Overcast forming over the
surface circulation.  Subjective Dvorak classifications from TAFB
and SAB, and a recent objective ADT current intensity estimate
yields an initial intensity of 40 kt for this advisory.  The shear
is forecast to remain relatively light and from the east to
southeast during the next 3-4 days.  Warm sea surface temperatures
and an atmospheric environment conducive for further strengthening
should allow the cyclone to intensify during the next 96 hours and
become a hurricane in 36 hours.  Afterwards, the upper level winds
become less favorable as Ignacio approaches an established mid- to
upper level trough near the Hawaiian Islands.  The NHC intensity
forecast is similar to the previous advisory and is based on a
compromise of the HWRF hurricane model and the IVCN intensity
consensus.

Based on Visible imagery and a recent microwave image from the GPM
satellite, Ignacio appears to have been moving west-southwestward
during the past 12-18 hours, and has recently turned more toward the
west or, 260/05 kt.  Ignacio should continue moving in this general
direction during the next 24 hours or so within the southwestern
peripheral flow of the subtropical ridge.  After that time, a
gradual turn toward the west-northwest is expected as the cyclone
rounds the southwestern extent of the ridge.  The official forecast
track has again been shifted toward the left, primarily due to the
previous west-southwestward motion, and agrees with both the GFEX
(GFS/ECMWF blend) and the TVCX multi-model consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 12.3N 133.4W   40 KT  45 MPH
 12H  26/1200Z 12.2N 134.8W   50 KT  60 MPH
 24H  27/0000Z 12.3N 136.5W   60 KT  70 MPH
 36H  27/1200Z 12.8N 138.3W   65 KT  75 MPH
 48H  28/0000Z 13.6N 140.1W   75 KT  85 MPH
 72H  29/0000Z 14.9N 143.4W   85 KT 100 MPH
 96H  30/0000Z 16.4N 146.9W   75 KT  85 MPH
120H  31/0000Z 17.7N 150.6W   70 KT  80 MPH

$$
Forecaster Roberts

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