[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 141450
TCDAT5

TROPICAL STORM IAN DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102016
1100 AM AST WED SEP 14 2016

Ian's center has lost some definition and appears to have re-formed
north of the feature we had been tracking.  The center remains
exposed to the south and southeast of the deep convection due to
almost 30 kt of vertical shear.  Based on the Dvorak Current
Intensity number from TAFB, the estimated maximum winds remain 45
kt.

Due to the center's re-formation, the initial motion is a faster
355/17 kt.  However, unless the center jumps again, this motion is
expected to stabilize back to around 14 kt in the next 12 hours.  A
mid-/upper-level low to the west of Ian and a mid-tropospheric high
to the east should steer the cyclone northward and north-
northeastward during the next day or so.  After that time, Ian is
expected to accelerate toward the northeast as it gets picked up by
a progressive mid-latitude trough moving eastward from Atlantic
Canada.  The new track guidance agrees on this scenario, although a
slight westward shift in the official track forecast was required,
probably due to the updated initial position.  The new NHC forecast
is very close to the TVCN multi-model consensus.

Although the vertical shear is expected to decrease only slightly,
marginally warm waters and Ian's baroclinic interaction with the
mid-/upper-level low to its west are expected to foster some
strengthening during the next 36 hours.  Ian is then expected to
lose the last of its tropical characteristics and become
extratropical by 48 hours and then be absorbed by another
extratropical low by 72 hours.  This forecast follows guidance
provided by the Ocean Prediction Center and is closest to the
scenario shown by the ECMWF model.  There is still some uncertainty
in this thinking, however, since the GFS, UKMET, and Canadian models
make Ian the dominant extratropical low over the far northern
Atlantic.

FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 31.4N  53.0W   45 KT  50 MPH
 12H  15/0000Z 33.7N  52.8W   50 KT  60 MPH
 24H  15/1200Z 36.7N  51.1W   50 KT  60 MPH
 36H  16/0000Z 40.2N  46.9W   55 KT  65 MPH
 48H  16/1200Z 45.4N  39.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  17/1200Z...DISSIPATED

$$
Forecaster Berg
This weather bulletin was brought to you by:
www.nashvilleweather.net