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TROPICAL DEPRESSION TWENTY-ONE-E SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
1000 AM MDT WED NOV 18 2015

The circulation associated with the low pressure system located
several hundred miles south-southeast of the southern tip of Baja
California has become well-defined overnight according to
scatterometer data.  These data and first-light visible satellite
imagery also indicate the that center of the cyclone is near the
southeastern edge of large mass of cold-topped convection,
suggesting the presence of some southeasterly shear.  A Dvorak
classification of T2.0 from TAFB, along with the earlier
scatterometer data, is used to set the intensity to 30 kt.

Since the history of fixes on this system is short, the initial
motion estimate of 360/02 is somewhat uncertain.  A deep trough over
the central United States has created a significant weakness along
110W, which has made for a weak steering environment around the
depression.  However, a weak mid-level anticyclone to the south of
mainland Mexico has been imparting a slow northward motion.  This
motion should continue for another 24 hours, at which time a
mid-level ridge over the Gulf of Mexico is forecast to build
westward into the eastern Pacific when the central U.S. trough lifts
out.  The building ridge should result in a northwestward and then a
west-northwestward track through 72 hours.  After that time, a
trough currently between 130W and 140W in the subtropics is forecast
to eject eastward toward the cyclone and result in its recurvature
in about 96 hours.  The official forecast track is on the left side
of the guidance envelope, closest to the ECMWF and GFS solutions,
and generally near the multi-model consensus.

There are mixed signals on the potential for intensification in the
short term.  Although the waters are anomalously warm, some
southeasterly shear is likely to continue to affect the cyclone over
the next day or two, along with some drying of the lower to middle
troposphere.  These large-scale conditions suggest that some
strengthening should occur, but it likely would be tempered by these
two negative factors.  Around 72 hours, the cyclone should encounter
an environment of increasing south-southwesterly or southwesterly
shear associated with the trough advancing from the west and rapidly
weaken, likely becoming a remnant low by day 5, if not sooner.  The
official intensity forecast is a little above the multi-model
consensus and closest to the ECMWF SHIPS output.


FORECAST POSITIONS AND MAX WINDS

INIT  18/1600Z 13.0N 107.2W   30 KT  35 MPH
 12H  19/0000Z 13.3N 107.2W   35 KT  40 MPH
 24H  19/1200Z 13.8N 107.5W   40 KT  45 MPH
 36H  20/0000Z 14.8N 108.6W   45 KT  50 MPH
 48H  20/1200Z 15.8N 110.6W   50 KT  60 MPH
 72H  21/1200Z 16.4N 113.0W   45 KT  50 MPH
 96H  22/1200Z 18.1N 114.2W   30 KT  35 MPH
120H  23/1200Z 20.5N 114.4W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kimberlain

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