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TROPICAL STORM IDA DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
500 PM AST TUE SEP 22 2015

The low-level center of Ida has been placed in the middle of a gyre
defined by several small vortices. The cyclone is still sheared with
the strongest convection located within a cyclonically- curved band
to the south of the center. Given the lack of scatterometer data,
and little change in the satellite presentation, the initial
intensity is kept at 40 kt.

Ida is embedded within the southern end of a mid-level trough, which
is forcing the cyclone to drift east-southeastward at about 4 kt,
and is also causing shear over the cyclone. The evolution of this
trough will be crucial for the future of Ida. Global models indicate
that Ida will drift generally eastward embedded in the trough for
the next 48 hours. After that time, most of the models lift the
trough out, leaving Ida south of an amplifying ridge. This long
range forecast pattern should result in the cyclone turning toward
the north-northwest as indicated in the NHC forecast, and also a
decrease of the shear with favorable conditions for strengthening.
Since the environment is currently quite hostile, no important
change in intensity is indicated during the next 3 days. By the end
of the forecast period, when the cyclone becomes detached from the
trough, some slight increase in strength is forecast.

The NHC track forecast continues to be in the middle of the guidance
envelope, and is very close to the ECMWF and GFS consensus. If the
global models are correct, Ida will be meandering over the Atlantic
for several more days.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 20.5N  47.8W   40 KT  45 MPH
 12H  23/0600Z 20.2N  47.2W   40 KT  45 MPH
 24H  23/1800Z 20.0N  46.5W   40 KT  45 MPH
 36H  24/0600Z 20.0N  46.0W   40 KT  45 MPH
 48H  24/1800Z 20.5N  45.5W   40 KT  45 MPH
 72H  25/1800Z 22.5N  45.7W   40 KT  45 MPH
 96H  26/1800Z 24.5N  47.0W   50 KT  60 MPH
120H  27/1800Z 26.5N  46.5W   55 KT  65 MPH

$$
Forecaster Avila

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