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TROPICAL STORM IAN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102016
500 PM AST MON SEP 12 2016

Ian remains poorly organized, with the bulk of the deep convection
displaced well to the northeast of the low-level center due to
strong vertical shear.  The advisory intensity estimate remains at
35 kt in agreement with a Dvorak estimate from TAFB.  The global
models suggest that some decrease in shear will occur in 36 to 48
hours, when the system moves on the northeast side of a partially
cut off upper-level cyclone.  This could permit a little
strengthening to commence around that time, as reflected in the
official forecast. This is slightly above the latest numerical model
intensity consensus.  By the end of the forecast period, or sooner,
Ian should become embedded in a frontal zone over the north Atlantic
and be transformed into an extratropical cyclone.

Ian has turned to the right, and the initial motion estimate is now
about 330/11 kt.  The storm continues to move through a break in
the subtropical ridge, and in a few days the flow ahead of a
mid-tropospheric trough should cause Ian to accelerate
north-northeastward to northeastward.  The official forecast lies
between the latest GFS and ECMWF predictions, and is also close to
the dynamical model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  12/2100Z 22.9N  50.7W   35 KT  40 MPH
 12H  13/0600Z 24.3N  51.7W   35 KT  40 MPH
 24H  13/1800Z 26.2N  52.9W   35 KT  40 MPH
 36H  14/0600Z 28.5N  54.0W   40 KT  45 MPH
 48H  14/1800Z 30.7N  54.5W   45 KT  50 MPH
 72H  15/1800Z 35.7N  52.4W   50 KT  60 MPH
 96H  16/1800Z 45.0N  42.0W   50 KT  60 MPH
120H  17/1800Z 54.5N  29.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch

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