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Tropical Depression Sixteen Discussion Number   4
NWS National Hurricane Center Miami FL       AL162017
500 AM EDT Thu Oct 05 2017

Deep convection associated with the depression has increased over
the eastern portion of the circulation overnight, however there
has only been a slight increase in overall banding.  Subjective
Dvorak intensity estimates suggest that the depression is near
tropical-storm strength, but with the center located near the
western edge of the deep convection the cyclone is kept as
a 30-kt tropical depression for this advisory.

The intensity forecast remains quite uncertain due to expected land
interaction today, and possibly again in about 48 hours when the
system passes near the Yucatan peninsula.  The depression could
still become a tropical storm before the center moves over
northeastern Nicaragua and eastern Honduras later today.  After the
cyclone moves north of Honduras, it will traverse the warm waters of
the northwestern Caribbean Sea, where the upper-level environment is
also forecast to be conducive for strengthening. However, the amount
of strengthening is likely to depend on the structure of the inner
core after it crosses land. The intensity models have continued
their downward trend, but the NHC forecast remains near the higher
side of the guidance due to these favorable conditions and
persistence from the previous advisory.  Some additional
strengthening is possible while the system moves over the southern
and central Gulf of Mexico, and the NHC intensity forecast brings
the system to hurricane strength within 72 hours.  This is in best
agreement with the SHIPS intensity model.

The depression is moving northwestward or 315/6 kt.  The cyclone is
forecast to move northwestward to north-northwestward during the
next day or two around the western side of a ridge the extends from
near the southeastern Bahamas southwestward into the central
Caribbean Sea. By the weekend, a large mid- to upper-level ridge is
forecast to build off the coast of the southeastern United States,
and this should steer the cyclone north-northwestward at a faster
forward speed.  After 72 hours, the system is expected to recurve
around the northwestward side of the ridge.  The track guidance is
in better agreement this cycle with the latest runs of the ECMWF
and UKMET models shifting westward, closer to the previous GFS and
HWRF iterations.  This has required a fairly substantial westward
shift in the NHC forecast track at 72 h and beyond.


KEY MESSAGES:

1. The depression is forecast to strengthen and bring tropical storm
conditions to portions of Nicaragua and Honduras through early
Friday.  Heavy rainfall could produce life-threatening flash
flooding and mud slides in portions of Nicaragua, Honduras, Costa
Rica, and Panama through Friday night.

2. The system could be near hurricane intensity when it approaches
the Yucatan Peninsula late Friday, bringing direct impacts from
wind, storm surge, and heavy rainfall, and a hurricane watch is
in effect for a portion of this area.

3. The system is forecast to strengthen 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, location,
or magnitude of these impacts.  Residents along the Gulf Coast from
Louisiana through the Florida Panhandle should monitor the progress
of this system and heed any advice given by local officials.


FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 13.3N  83.3W   30 KT  35 MPH
 12H  05/1800Z 14.3N  83.9W   30 KT  35 MPH...INLAND
 24H  06/0600Z 16.3N  84.8W   35 KT  40 MPH
 36H  06/1800Z 19.0N  86.0W   45 KT  50 MPH
 48H  07/0600Z 21.8N  87.4W   55 KT  65 MPH
 72H  08/0600Z 27.8N  89.5W   65 KT  75 MPH
 96H  09/0600Z 34.0N  86.5W   35 KT  40 MPH...INLAND
120H  10/0600Z 39.5N  79.0W   25 KT  30 MPH...POST-TROP/INLAND

$$
Forecaster Brown

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