000
WTPZ41 KNHC 200844
TCDEP1

TROPICAL STORM RICK DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
200 AM MST FRI NOV 20 2015

Rick is sending mixed signals tonight with regard to its
organization and intensity.  On one hand, the convective banding is
a little better defined, and Dvorak T-numbers are now T3.0 from SAB
and T2.5 from TAFB.  On the other hand, recent scatterometer data
indicate that the maximum winds remain about 35 kt, with the
tropical-storm-force winds confined to a small area west of the
center.

The initial motion remains west-northwestward, or 295/11 kt.  A
mid-level ridge that extends westward across central Mexico is
forecast to build farther westward over the Pacific waters during
the next 24 hours, which should keep the cyclone on a west-
northwestward course for the next couple of days.  By Sunday, the
western extent of the ridge will be eroded by a shortwave trough,
causing Rick to turn gradually northwestward and northward on days
3-5.  The track models all agree on this general scenario, but the
overall guidance envelope has shifted westward from the previous
cycle, especially beyond 36 hours.  Therefore, the updated NHC track
forecast is also shifted westward and lies very close to the TVCE
model consensus and the Florida State Superensemble.

Deep-layer shear near Rick is very low at the moment and should
remain generally light for the next 36-48 hours.  In addition, sea
surface temperatures are sufficiently warm for intensification.
However, a major limiting factor appears to be the presence of
mid-level dry air, with the 700-500 mb relative humidity expected to
remain around 50 percent for the next few days.  Therefore, only
slight strengthening is anticipated in the short term.  After 48
hours, a marked increase in southwesterly shear should cause Rick to
weaken and degenerate to a remnant low, possibly as early as 72
hours, when the associated deep convection is sheared away from the
low-level center.  The latest global models suggest that the remnant
low may now last through 120 hours.  There is not much spread among
the intensity models, and the official intensity forecast mainly
follows the IVCN model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0900Z 15.9N 109.4W   35 KT  40 MPH
 12H  20/1800Z 16.5N 110.8W   40 KT  45 MPH
 24H  21/0600Z 17.1N 112.4W   40 KT  45 MPH
 36H  21/1800Z 17.6N 113.9W   40 KT  45 MPH
 48H  22/0600Z 18.1N 115.1W   40 KT  45 MPH
 72H  23/0600Z 20.1N 116.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  24/0600Z 22.0N 117.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  25/0600Z 22.5N 117.0W   15 KT  15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg