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TROPICAL STORM IAN DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102016
1100 PM AST WED SEP 14 2016

Water vapor imagery indicates that an upper-level low has moved
over and has become superimposed with Ian's low-level center. Broken
convective banding features, along with an abundance of lightning,
have developed northwest through northeast of the center. Drifting
buoy 41506, located about 20 nmi north of the center reported
1001.5 mb pressure at 0100Z. Another drifting buoy located about
150 nmi east of the center reported a pressure of around 1015 mb,
and the pressure difference between Ian and that buoy supports a
gradient wind of 50-52 kt. For now, the initial intensity of Ian
will remain at 45 kt since another scatterometer pass over the
cyclone is due shortly. Ship BATFR13 has been reporting winds of 30
kt about 250 nmi north-northeast of the center, which supports the
previous and current 34-kt wind radius of 200 nmi in that quadrant.

Ian has made the much anticipated turn toward the north-northeast,
and the cyclone is now moving 015/12 kt. Ian should gradually turn
more toward the northeast during the next 24 hours and accelerate
as the storm moves around the western portion of Bermuda-Azores
High, and ahead of an advancing strong shortwave trough. The new
forecast track is essentially just an extension of the previous
advisory track and lies down the middle of the tightly packed NHC
track model guidance.

Ian is looking more like a subtropical cyclone on conventional
satellite.  However, the recent increase in deep convection near and
within 75 nmi of the center, along with recent AMSU data indicating
that the system still has a mid- to upper-level warm-core structure,
support maintaining Ian as a tropical cyclone. Ian has about 24
hours or so remaining to intensify as a tropical cyclone while it is
located south of the Gulf Stream and over warm waters. By 36 hours,
Ian will lose its tropical characteristics over cooler water, but
some baroclinic forcing is expected to help strengthen the cyclone.
By 72 hours, Ian is expected to be absorbed by a larger
extratropical low. The intensity forecast remains unchanged from the
previous advisory and follows the trend of global models.

FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 33.9N  53.4W   45 KT  50 MPH
 12H  15/1200Z 36.3N  51.6W   50 KT  60 MPH
 24H  16/0000Z 40.3N  47.0W   50 KT  60 MPH
 36H  16/1200Z 45.8N  39.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 48H  17/0000Z 51.7N  32.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  18/0000Z...ABSORBED

$$
Forecaster Stewart

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