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Tropical Depression TWENTY-E


1000 AM CDT TUE OCT 20 2015

Satellite data indicate that deep convection associated with the
area of low pressure a few hundred miles southeast of Puerto
Escondido, Mexico, has become sufficiently well organized to
designate the system as a tropical depression.  The circulation of
the low has also become better defined according to an overnight
ASCAT pass, though it could still be somewhat elongated to the
south.  The depression's cloud pattern is characterized by
interlocking convective bands, with the estimated low-level center
underneath the eastward tip of the western band.  A Dvorak intensity
estimate of T2.0 from TAFB is used to set the initial intensity at
30 kt.

Since the center location uncertainty has been high until
very recently, the initial motion estimate is a rather uncertain
280/02.  The track guidance is in very good agreement that a
mid-level ridge over the Gulf of Mexico with an east-northeast to
west-northwest orientation should impart a west-southwestward motion
for about 24 hours.  A turn toward the west and west-northwest
with some increase in forward speed is forecast by 36 hours once the
ridge over the Gulf of Mexico shifts eastward.  When the cyclone
reaches the western edge of ridge around 72 hours, it should turn
northwestward.  The evolution of a deep longwave trough over the
southwestern U.S. and northwestern Mexico is of critical
importance to the track forecast after that time as the cyclone
nears the southwestern coast of Mexico. There are differences
between the models regarding the timing and strength of a shortwave
trough dropping into the southwestern U. S. during this period,
resulting in increasing spread of the track guidance after 72
hours.  The track forecast is close to the multi-model consensus,
but it is a little west of the GFS and ECMWF solutions beyond day 3.

The large-scale environment around the cyclone is forecast to be
quite conducive for intensification during the next few days, with
SSTs to above 30 deg C, a rich moisture supply in the lower to
middle troposphere, and very light vertical shear.  The main
limiting factor should be how quickly the cyclone develops enough
inner-core organization to potentially rapidly intensify.  Prior to
landfall, an increase in southwesterly vertical shear and drier air
associated with the mid-to upper-level trough to the northwest could
result in weakening, with a peak intensity mostly likely between the
72- and 96-hour points.  The NHC intensity forecast is above the
multi-model consensus and in best agreement with the LGEM output
until the forecast landfall.  Dissipation is shown after 96 hours,
though it could occur sooner over the high terrain of the Sierra
Madre Occidental.


INIT  20/1500Z 13.3N  94.4W   30 KT  35 MPH
 12H  21/0000Z 13.0N  95.5W   35 KT  40 MPH
 24H  21/1200Z 12.8N  97.0W   45 KT  50 MPH
 36H  22/0000Z 12.9N  98.9W   55 KT  65 MPH
 48H  22/1200Z 13.9N 101.0W   70 KT  80 MPH
 72H  23/1200Z 16.3N 103.7W   85 KT 100 MPH
 96H  24/1200Z 20.5N 104.4W   50 KT  60 MPH...INLAND
120H  25/1200Z...DISSIPATED

Forecaster Kimberlain