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Tropical Depression SIXTEEN


Tropical Depression Sixteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL162017
1100 AM EDT Wed Oct 04 2017

Satellite images indicate that the area of low pressure in the
southwestern Caribbean Sea has become better organized since
yesterday and is now a tropical depression.  GOES-16 one-minute
visible data suggest the center is in between two large curved bands
of deep convection, not too far from San Andres Island.  The initial
wind speed is set to 30 kt, somewhat above the TAFB satellite
classification, given recent microwave data.  An Air Force Reserve
Hurricane Hunter aircraft should be in the area this afternoon to
provide a better estimate.

Other than land interaction between 24-36 hours, environmental
conditions look conducive for intensification of the depression.  A
large mid/upper-level trough is forecast to drop over the SW Gulf of
Mexico, providing a low-shear environment for the cyclone. Rapid
intensification is a possibility over the northwestern Caribbean or
southern Gulf of Mexico while the system is traversing rather warm
and deep waters, although it remains to be seen how separate the
depression becomes from a larger gyre over central America.  The
official intensity forecast is close to the SHIPS model, on the
high side of the intensity guidance since much of the GFS-based
tracks show much more land interaction than the official forecast.

The depression is moving slowly northwestward this morning, around
a distant mid-level ridge over the southwestern Atlantic Ocean.
However the steering pattern should change quickly tomorrow as the
aforementioned mid-tropospheric trough moves across the northwestern
Caribbean into the southwestern Gulf of Mexico. Southerly flow on
the eastern side of that trough should cause the cyclone to move
much faster to the north-northwest by Friday and northward into the
Gulf of Mexico on Saturday.  As the trough moves away, a building
ridge over the southwestern Atlantic is forecast to steer the system
to the north-northeast or northeast toward the northern Gulf
states. There is a fair bit of model spread for now, partly owing to
the representation of the Florida Straits trough.  The GFS-based
guidance seems to over-amplify the trough, which causes the
new tropical cyclone to be pulled northwestward longer than most of
the rest of the models. Consequently, this forecast is closer to the
UKMET and ECMWF models, on the right side of the model consensus,
but must be considered a low-confidence prediction at this time.


1. The depression is forecast to strengthen and bring tropical storm
conditions and heavy rainfall to portions of Nicaragua and Honduras
tonight through Thursday.

2. The system is forecast to continue strengthening over the Gulf of
Mexico and could affect portions of the northern Gulf Coast as a
hurricane this weekend, with direct impacts from wind, storm surge,
and heavy rainfall.  However, it is too early to specify the timing
or magnitude of these impacts. Residents along the Gulf Coast from
Louisiana to Florida should monitor the progress of this system for
the next several days and heed any advice given by local officials.


INIT  04/1500Z 12.2N  81.9W   30 KT  35 MPH
 12H  05/0000Z 12.7N  82.6W   35 KT  40 MPH
 24H  05/1200Z 13.8N  83.5W   40 KT  45 MPH...INLAND
 36H  06/0000Z 15.3N  84.1W   35 KT  40 MPH...INLAND
 48H  06/1200Z 17.9N  85.0W   45 KT  50 MPH
 72H  07/1200Z 23.5N  87.0W   60 KT  70 MPH
 96H  08/1200Z 29.0N  86.0W   70 KT  80 MPH
120H  09/1200Z 34.5N  82.5W   30 KT  35 MPH...POST-TROP/INLAND

Forecaster Blake