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TROPICAL DEPRESSION TWENTY-ONE-E DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
200 PM MST WED NOV 18 2015
 
Overall, the cyclone's cloud pattern has changed little in
organization since the previous advisory.  The center of the
depression is on the southeastern edge of a large cluster of deep
convection, indicative of a continuation of moderate southeasterly
shear.  A well-defined swirl is also seen in visible satellite
imagery, rotating around the south side of the estimated mean
center. Satellite intensity estimates are a consensus T2.0 from TAFB
and SAB, and the initial intensity estimate is held at 30 kt.
 
The center has been moving erratically during the last 6 to 12
hours, with fixes during this time indicating a nearly stationary
initial motion.  The tail of a deep mid- to upper-level trough over
the central United States extends southwestward to just north of the
depression, which has created a weakness near 110W.  The weakness
has created a weak steering environment that should persist for
about the next 12 to 24 hours and result in the depression's moving
erratically or slowly northward around a weak mid-level high to the
east.  A turn toward the northwest and then west-northwest is
expected after that time with an increase in forward speed when a
mid-level anticyclone over the Gulf of Mexico builds westward into
the eastern Pacific to the north of the cyclone.  After that time, a
trough currently between 130W and 140W in the subtropics is forecast
to eject eastward toward the cyclone and result in a northward turn
in 96 hours.  The new track forecast is much faster than the
previous forecast and adjusted to the left, especially beyond 48
hours, but is not as far west as the multi-model consensus.
 
SHIPS model output indicates a lessening of southeasterly shear over
the depression within 24 hours, with the shear remaining relatively
low through about 72 hours.  Meanwhile, the lower- to mid-
tropospheric moisture is forecast to decrease some and be only
marginally conducive for strengthening.  However, since the cyclone
should be over anomalously warm waters during this period,
intensification is forecast, especially after the shear decreases.
After 72 hours, a tremendous increase in southwesterly shear ahead
of the trough advancing from the west should result in rapid
weakening, with remnant low status likely in 96 to 120 hours.  The
new intensity forecast is a bit higher than the previous one in
agreement with the latest SHIPS/LGEM guidance and remains slightly
above the multi-model consensus.
 
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/2100Z 12.8N 107.0W   30 KT  35 MPH
 12H  19/0600Z 13.4N 107.2W   35 KT  40 MPH
 24H  19/1800Z 14.3N 108.4W   40 KT  45 MPH
 36H  20/0600Z 15.2N 110.1W   50 KT  60 MPH
 48H  20/1800Z 15.6N 111.5W   55 KT  65 MPH
 72H  21/1800Z 17.2N 114.5W   60 KT  70 MPH
 96H  22/1800Z 18.6N 115.8W   30 KT  35 MPH
120H  23/1800Z 20.5N 116.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Kimberlain
 
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