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TROPICAL DEPRESSION IDA DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 PM AST THU SEP 24 2015

The center of Ida, like most of the Atlantic tropical cyclones this
year at some point, is exposed to southwest of a bursting area
of deep convection.  The initial intensity is kept at 30 kt in
accordance with the latest TAFB Dvorak classification. A combination
of shear and dry air aloft is expected to persist near Ida for the
next few days.  These conditions are forecast to cause the cyclone
to gradually weaken.  Although the cyclone could move into a
slightly more favorable environment at long range, there isn't
likely to be much left of Ida to take advantage of the conditions.
The latest NHC forecast is close to the model consensus for the
first few days, then is below that aid at days 3 and 4, leaning more
heavily on the weaker solutions of the HWRF, GFS and ECMWF models.
Both the GFS and the ECMWF now show Ida opening up into a trough by
day 5, and the official forecast follows that trend.

Ida is moving erratically north-northwestward at about 4 knots. The
depression should turn northwestward tomorrow and head in that
general direction for a couple of days due to a weak subtropical
ridge forming over the central Atlantic.  After that time, the
cyclone is expected to be a shallow system, and will likely move
to the west or west-southwest as it is steered by a strong low-level
ridge. The guidance has shifted leftward, which makes sense for a
weaker cyclone, and the official NHC prediction follows suit.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0300Z 21.3N  45.3W   30 KT  35 MPH
 12H  25/1200Z 21.9N  45.6W   30 KT  35 MPH
 24H  26/0000Z 22.8N  46.3W   25 KT  30 MPH
 36H  26/1200Z 23.7N  47.2W   25 KT  30 MPH
 48H  27/0000Z 24.4N  48.0W   25 KT  30 MPH
 72H  28/0000Z 24.3N  49.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  29/0000Z 24.0N  51.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  30/0000Z...DISSIPATED

$$
Forecaster Blake

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