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Tropical Storm IDA (Text)


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TROPICAL STORM IDA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 AM AST SAT SEP 19 2015

As was noted yesterday, Ida will have an obstacle course to navigate
during the next several days, and the storm already appears to have
encountered its first hurdle.  Westerly shear, on the order of 20 kt
according to UW-CIMSS analyses, has begun to affect the cyclone, and
the low-level center is now exposed to the northwest of the deep
convection.  Dvorak CI numbers remain 2.5, and the initial intensity
therefore remains 35 kt.  The SHIPS guidance indicates that the
vertical shear should be steady or even increase slightly during the
next 24 hours, so only slow strengthening is anticipated during that
time.  The best window for more significant intensification appears
to be between 36 and 72 hours when the shear is forecast to
decrease.  Another round of increased shear on days 4 and 5 should
limit strengthening or induce weakening.  The intensity models are
split on Ida's future intensity, with the SHIPS and LGEM models only
modestly strengthening the cyclone through day 5 while the GFDL and
HWRF models bring Ida to hurricane strength by day 3.  Due to the
uncertainty of how Ida will interact with the complex environment
around it, the NHC intensity forecast is a bit below the intensity
consensus and is very similar to the previous forecast.

Low- to mid-level ridging to the north and northeast of Ida is
inducing a slightly faster west-northwestward motion, or 295/10 kt.
The ridge is expected to weaken within the next 48 hours, leaving
Ida between two deep-layer lows, one located over the eastern
Atlantic and the other northeast of the Leeward Islands.  This
should cause Ida to become nearly stationary or meander by days 3
through 5. With the exception of the UKMET model, the other track
models seem to be trending toward a solution in which the eastern
Atlantic trough has at least some influence on Ida's motion, and the
updated NHC track forecast now shows a slow eastward drift on days 4
and 5. Overall though, the NHC track forecast is very similar to the
previous one and is close to the model consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 14.8N  39.7W   35 KT  40 MPH
 12H  20/0000Z 15.7N  41.4W   40 KT  45 MPH
 24H  20/1200Z 16.9N  43.4W   45 KT  50 MPH
 36H  21/0000Z 18.2N  45.1W   50 KT  60 MPH
 48H  21/1200Z 19.3N  46.5W   55 KT  65 MPH
 72H  22/1200Z 20.5N  47.5W   60 KT  70 MPH
 96H  23/1200Z 20.5N  47.0W   60 KT  70 MPH
120H  24/1200Z 20.5N  46.5W   55 KT  65 MPH

$$
Forecaster Berg

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Page last modified: Thursday, 31-Dec-2015 12:09:19 UTC