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TROPICAL STORM IDA DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 PM AST WED SEP 23 2015

Ida is not a well-organized tropical storm.  The center is on the
western side of a small area of deep convection, with a few banding
features noted in the southeastern quadrant of the cyclone.  The
initial intensity remains 35 kt since a recent partial ASCAT pass
showed maximum winds of 30-35 kt.

The storm continues to experience moderate-to-strong westerly shear.
While the shear could relax somewhat over the next couple of days,
very dry air is present in the mid- to upper-levels near and to the
northwest of the cyclone, which could prevent Ida from fully taking
advantage of the more favorable shear conditions for a few days.
The latest NHC intensity forecast is close to the previous one and
the intensity consensus.  At longer range, some of the models are
showing a resumption of the stronger shear, with only the GFDL
forecasting significant intensification.  Overall, the trend has
been toward a less favorable environment at day 5, and the NHC
intensity forecast is reduced at that time.

Ida is moving eastward at about 4 kt while it remains embedded
within the base of a mid- to upper-level trough.  This trough is
expected to lift out tomorrow with a ridge rebuilding over the
central Atlantic.  This pattern should cause the storm to move to
the north by late Thursday, followed by a turn to the northwest on
Friday around the ridge.  After that time, another mid-latitude
trough is expected to affect the cyclone.  This feature, however, is
not as deep as the last trough, and with the vertical representation
of Ida being shallower in the model fields, much of the guidance is
only show Ida stalling for a short amount of time rather than
turning with the trough.  Another ridge builds in by late weekend,
which then forces Ida to move west-northwestward and westward by
early next week. The guidance has shifted notably westward on this
cycle in response to this pattern, and the NHC forecast is shifted
that direction at long range, but is still pretty far east of the
model consensus due to continuity concerns.


FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 19.9N  46.0W   35 KT  40 MPH
 12H  24/1200Z 20.3N  45.5W   35 KT  40 MPH
 24H  25/0000Z 21.0N  45.7W   35 KT  40 MPH
 36H  25/1200Z 21.8N  46.2W   35 KT  40 MPH
 48H  26/0000Z 22.7N  46.9W   35 KT  40 MPH
 72H  27/0000Z 24.2N  48.4W   40 KT  45 MPH
 96H  28/0000Z 24.5N  49.0W   45 KT  50 MPH
120H  29/0000Z 24.5N  50.5W   45 KT  50 MPH

$$
Forecaster Blake

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