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TROPICAL DEPRESSION IDA DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 PM AST FRI SEP 25 2015

The depression consists of a swirl of low clouds with pulsing
convection in the eastern part of the circulation.  Although Ida
isn't very impressive on satellite imagery, the latest ASCAT data
showed a small area of 30-35 kt winds in the southeastern quadrant
of the cyclone.  Since the convective structure has degraded since
the ASCAT pass and the Dvorak estimates are low, the initial wind
speed is conservatively set to 30 kt.

Ida is still forecast, albeit with low confidence, to decay into a
remnant low in 24 h while the cyclone remains in a high shear, low
moisture environment during the next day or so.  Global and
regional model guidance, however, are starting to suggest that Ida
will encounter a more favorable environment in 2-3 days with less
shear and warmer waters, with only the GFS model now showing
dissipation. In fact, most of the guidance brings the cyclone back
to tropical storm strength by day 5.  I'd like to see more
consistent guidance before forecasting that solution, but as a
compromise, the new prediction calls for Ida to regenerate as
tropical depression, but with limited strengthening.  While the new
forecast is above the previous one, it is below almost all of the
guidance except for the GFS.

Ida is moving faster toward the north-northwest tonight at about 7
kt. The cyclone is forecast to turn northwestward tomorrow,
westward on Sunday and then west-southwestward while Ida moves
around a strengthening mid-level ridge over the central Atlantic.
Models have come into better agreement on this scenario, although
the ECMWF remains a bit of a slow outlier.  The official forecast is
shifted southwestward, but lies on the northern side of the guidance
envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 22.9N  45.5W   30 KT  35 MPH
 12H  26/1200Z 23.6N  46.3W   30 KT  35 MPH
 24H  27/0000Z 24.3N  47.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  27/1200Z 24.3N  47.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  28/0000Z 23.7N  48.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  29/0000Z 22.7N  51.5W   30 KT  35 MPH
 96H  30/0000Z 22.1N  54.6W   30 KT  35 MPH
120H  01/0000Z 22.5N  57.5W   30 KT  35 MPH

$$
Forecaster Blake

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