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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 PM AST WED SEP 14 2016

The convective pattern of the depression has improved some since the
previous advisory with short curved bands having developed in all
quadrants. In addition, the upper-level outflow has also improved
and become more symmetrical. Satellite intensity estimates range
from 30 kt from TAFB and SAB, 37-41 kt in recent AMSU estimates, and
an ADT value of T2.8/41 kt. Due to the lack of persistent inner-core
convection, the intensity is being maintained at 30 kt.

The initial motion is 280/12 kt.  A deep-layer ridge to the north
of the cyclone is expected steer the system west-northwestward and
then westward during the next 48 hours, accompanied by some
decrease in forward speed as the ridge weakens slightly. By 72
hours and beyond, the ridge is forecast to build southward slightly,
forcing the cyclone on a west-southwestward track over warmer
waters. The new forecast track is basically just an update of the
previous advisory track, and lies close to the consensus models.

Some strengthening is expected during the next 24 hours or so. After
that, the cyclone will encounter moderate to strong westerly
vertical wind shear caused by a developing upper-level trough to the
north of the cyclone.  The new intensity forecast continues to show
the system weakening back to a depression by 36 hours. On days 4
and 5, some slight re-strengthening is expected when the cyclone
moves over SSTs near 28 deg C and into more favorable mid- and
upper-level environments as shown by the ECMWF and UKMET models.

FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 17.6N  27.5W   30 KT  35 MPH
 12H  15/1200Z 17.8N  29.4W   35 KT  40 MPH
 24H  16/0000Z 18.0N  31.9W   35 KT  40 MPH
 36H  16/1200Z 18.1N  34.3W   30 KT  35 MPH
 48H  17/0000Z 17.9N  36.6W   30 KT  35 MPH
 72H  18/0000Z 17.5N  40.7W   30 KT  35 MPH
 96H  19/0000Z 17.4N  44.6W   35 KT  40 MPH
120H  20/0000Z 17.9N  49.0W   40 KT  45 MPH

$$
Forecaster Stewart

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