000
WTPZ41 KNHC 210836
TCDEP1

TROPICAL STORM RICK DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
200 AM MST SAT NOV 21 2015

Rick has been moving quickly west-northwestward into a drier air
mass, with all its associated deep convection lagging to the south
and southeast of the low-level center.  The initial intensity
remains 35 kt based on Dvorak CI numbers of 2.5 from TAFB and SAB,
but if the convective organization doesn't improve, these numbers
are likely to fall below the tropical storm threshold soon.
Vertical shear is expected to increase substantially in about 36
hours, and the cyclone will continue to move toward cooler water and
into an environment where the mid-level relative humidity is less
than 50 percent.  Therefore, Rick will likely weaken to a tropical
depression sometime during the next 24 hours and degenerate to a
remnant low by 48 hours.  The updated NHC intensity forecast closely
follows the SHIPS and LGEM guidance.

A mid-level ridge extending westward from southern and central
Mexico is steering Rick west-northwestward with an initial motion
of 285/10 kt.  A mid- to upper-level trough located between 125W
and 140W is expected to move eastward and erode the western extent
of the ridge during the next day or two, causing Rick to slow down
and turn northwestward.  After 48 hours, the remnant low should
turn northward and slow down further in a weaker lower-tropospheric
flow regime.  No changes were required to the previous NHC track
forecast, and the new one is close to the multi-model consensus of
the dynamical models, with extra weight given to the typically
skillful ECMWF model.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 16.9N 113.8W   35 KT  40 MPH
 12H  21/1800Z 17.2N 114.9W   35 KT  40 MPH
 24H  22/0600Z 17.9N 116.4W   30 KT  35 MPH
 36H  22/1800Z 19.0N 117.8W   30 KT  35 MPH
 48H  23/0600Z 20.1N 118.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  24/0600Z 21.8N 119.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  25/0600Z 22.5N 118.5W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  26/0600Z...DISSIPATED

$$
Forecaster Berg