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TROPICAL STORM IAN DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102016
1100 AM AST TUE SEP 13 2016

Ian remains a sheared tropical storm, with the low-cloud center
exposed to the south of the main area of deep convection.  The
current intensity estimate remains 40 kt, since the system has not
become better organized since the time of the last scatterometer
pass.  The strong shear over Ian is being produced by an upper-level
low a couple of hundred miles to the west-northwest.  The global
models predict this low to open up into a negatively-tilted trough,
with some slight relaxation of the shear over the storm, in 24-36
hours.  Therefore slight strengthening is shown by the official
forecast after 24 hours, in line with the latest model consensus.
The global model guidance depicts the cyclone to become frontal over
the north Atlantic by 96 hours, and this is also reflected in the
official forecast.

The tropical cyclone is moving north-northwestward at a slightly
faster forward speed, or around 330/11 kt.  Ian is expected to
continue to move through a weakness in the mid-level subtropical
ridge over the next day or so.  Then, an approaching trough in the
westerlies should cause the cyclone to turn north-northeastward and
accelerate.  The official track forecast is a little faster than
the previous one, but not as fast as the latest GFS and ECMWF
model predictions.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 25.4N  52.3W   40 KT  45 MPH
 12H  14/0000Z 27.3N  53.0W   40 KT  45 MPH
 24H  14/1200Z 29.9N  53.7W   40 KT  45 MPH
 36H  15/0000Z 32.6N  53.8W   45 KT  50 MPH
 48H  15/1200Z 35.5N  52.5W   50 KT  60 MPH
 72H  16/1200Z 44.0N  42.4W   50 KT  60 MPH
 96H  17/1200Z 54.0N  28.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  18/1200Z 62.0N  13.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch

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