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TROPICAL DEPRESSION EIGHT SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082015
1230 AM AST WED SEP 09 2015

A recent ASCAT-B overpass indicates that the low pressure area
east-southeast of Bermuda has developed a well-defined circulation
with winds of at least 30 kt in the northeastern quadrant.  In
addition, a strong cluster of convection has been persisting in the
eastern quadrant.  Based on these developments, advisories are
being initiated on Tropical Depression Eight.  It should be noted
that the system has a large radius of maximum winds more
characteristic of a subtropical cyclone.  However, data from the
FSU phase space analysis and the strong convection suggest the
system is more tropical than subtropical.

The cyclone is currently nearly stationary.  A northward motion
should begin on Wednesday as a deep layer trough moves into the
eastern United States and weakens the subtropical ridge.  The
cyclone is expected to enter the westerlies and turn toward the
northeast after 48 hours, with this motion continuing until
dissipation.  The forecast track lies in the center of the track
guidance envelope in good agreement with the various consensus
models.

An upper-level trough just west of the cyclone is currently
providing upper-level difluence, and this is likely enhancing the
convection.  The dynamical models forecast the cyclone to become
embedded in about 15 kt of southerly vertical wind shear on the
east side of the trough.  While there is dry air entraining into
the cyclone, the environment should allow for some slow
strengthening through 72 hours while the system remains over warm
water.  Thus, the intensity forecast calls for strengthening in best
agreement with a blend of the SHIPS and LGEM models.  After 72
hours, the cyclone is expected to merge with a frontal system and
lose its identity by 120 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  09/0430Z 30.8N  61.5W   30 KT  35 MPH
 12H  09/1200Z 30.8N  61.5W   35 KT  40 MPH
 24H  10/0000Z 31.6N  61.5W   40 KT  45 MPH
 36H  10/1200Z 33.4N  61.9W   45 KT  50 MPH
 48H  11/0000Z 36.0N  62.2W   50 KT  60 MPH
 72H  12/0000Z 43.0N  60.5W   50 KT  60 MPH
 96H  13/0000Z 48.0N  45.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  14/0000Z...DISSIPATED

$$
Forecaster Beven

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