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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 AM AST WED SEP 14 2016

Satellite imagery, scatterometer data, and surface observations
indicate that the low pressure area over the Cabo Verde Islands has
developed a well-defined circulation and sufficient organized
convection to be considered a tropical depression.  The initial
intensity is set at 30 kt based on the scatterometer data along
with satellite intensity estimates from TAFB and SAB.

The initial motion is 300/12.  A low- to mid-level ridge should
steer the system west-northwestward and then westward during the
forecast period, with some decrease in forward speed after 36 hours
as the ridge weakens slightly.  The forecast track is near the
center of the guidance envelope and close to the various consensus
models.

Some strengthening is expected during the next 12-24 hours.  After
that, the cyclone is likely to encounter strong westerly vertical
wind shear while over sea surface temperatures of about 26C.  This
combination should lead to weakening, and the intensity forecast
shows the system weakening back to a depression by 36 hours.  Near
the end of the forecast period, the dynamical models diverge on the
evolution of the upper-level winds, with the ECMWF and UKMET
forecasting a more favorable pattern than the GFS. Based on this,
the forecast shows some re-intensification by 120 hours.  An
alternative scenario is that the cyclone degenerates to a tropical
wave as forecast by the GFS.  Overall, the intensity forecast is on
the low side of the guidance in best agreement with the LGEM.

Locally heavy rains and gusty winds are possible over the Cabo
Verde Islands.  However, current indications are that the cyclone
will not reach tropical-storm strength until it has moved west of
the islands.  Therefore, watches and warnings are not required at
this time.


FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 17.0N  25.0W   30 KT  35 MPH
 12H  15/0000Z 17.5N  26.8W   35 KT  40 MPH
 24H  15/1200Z 17.9N  29.3W   35 KT  40 MPH
 36H  16/0000Z 17.9N  31.7W   30 KT  35 MPH
 48H  16/1200Z 17.8N  34.0W   30 KT  35 MPH
 72H  17/1200Z 17.5N  38.0W   30 KT  35 MPH
 96H  18/1200Z 17.5N  41.5W   35 KT  40 MPH
120H  19/1200Z 18.0N  45.5W   40 KT  45 MPH

$$
Forecaster Beven

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