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TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
400 PM CDT SAT SEP 26 2015

Satellite imagery suggests that the area of low pressure several
hundred miles southwest of Acapulco, Mexico, has developed a well-
defined circulation and has enough organized deep convection to
be declared a tropical depression.  The initial wind speed is set to
30 kt in agreement with a Dvorak estimate from TAFB.

Recent fixes suggest an initial motion of 345/03, but it would not
be surprising if the motion were actually even more northerly. A
slow northward motion is expected during the next 24 to 36 hours as
the depression rounds the western side of a weak mid-level ridge
along 95W.  In about 36 h, the cyclone should encounter the
increasing westerly or west-southwesterly flow around a mid- to
upper-level trough over the northwestern Gulf of Mexico and turn
northeastward, a motion that could bring the cyclone's center inland
as predicted by the GFS and HWRF in 72 to 84 hours.  An alternative
scenario, supported by the ECMWF, is for the shear to become
prohibitively high just after 72 hours and result in a decoupling
of the cyclone. The shallow remnant circulation would then likely
drift west-northwestward in the low-level flow away from the coast.
The official track forecast brings the center close to the coast in
72 hours but does not explicitly show a landfall.  The overall track
forecast is weighted more heavily toward the ECMWF solution which
seems to have a better handle on the depression's initial motion.

Although the waters are plenty warm and the atmospheric moisture
high, westerly shear associated with the mid- to upper-level trough
over the Gulf of Mexico is expected to be an increasingly important
factor in the cyclone's intensification.  The shear should not be
high enough initially to prevent a climatological rate of
development during the next day or so.  However, global models show
at least 20 kt of shear in 36-48 hours, which makes significant
intensification less likely after that time.  The official intensity
forecast is between the statistical and dynamical guidance through
72 h and above the multi-model consensus.  Rapid weakening is
forecast after that time, either as a result of the cyclone's moving
inland or the possible decoupling of the cyclone.

FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 13.3N 103.0W   30 KT  35 MPH
 12H  27/0600Z 14.0N 103.1W   40 KT  45 MPH
 24H  27/1800Z 14.7N 103.1W   50 KT  60 MPH
 36H  28/0600Z 15.4N 102.9W   55 KT  65 MPH
 48H  28/1800Z 15.9N 102.6W   55 KT  65 MPH
 72H  29/1800Z 16.6N 101.6W   55 KT  65 MPH
 96H  30/1800Z 17.1N 102.1W   30 KT  35 MPH
120H  01/1800Z 17.2N 102.5W   30 KT  35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kimberlain

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