000
WTPZ42 KNHC 272035
TCDEP2

TROPICAL STORM MARTY DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
400 PM CDT SUN SEP 27 2015

Visible imagery shows that Marty has lost organization during the
past several hours due to 20-25 kt of westerly shear.  The low-level
center is now partly exposed to the southwest of the convection, and
the thunderstorm activity has decreased in both coverage and
intensity. A partial ASCAT-B overpass showed winds near 50 kt just
northwest of the center, and based on this the initial intensity
remains 50 kt.

The initial motion is a somewhat uncertain 005/3.  Marty is located
to the west of a mid-level ridge which extends across Central
America, and to the south of a deep-layer trough located over Mexico
and the southern United States.  The track guidance continues to
forecast a slow northeastward motion during the next 36 hours or so.
After that, there continues to be divergence in the guidance. The
GFS, Canadian, and NAVGEM models forecast Marty to move inland over
Mexico, while the UKMET and ECMWF show the system shearing apart,
with the low-level center turning westward.  The track forecast
favors the latter scenario and shows Marty making a westward turn
and staying offshore.  The new forecast track is again similar to
the previous advisory.

Marty remains in a moist airmass and over sea surface temperatures
of near 30C.  However, all of the dynamical guidance suggests the
cyclone should experience significant shear during the next 72
hours.  While several of the dynamical models still call for Marty
to become a hurricane, the SHIPS and LGEM models now forecast a peak
intensity of about 55 kt.  Given that the guidance and the current
trends, the intensity forecast is lowered from the previous forecast
and no longer calls for Marty to become a hurricane.  From 36-72
hours, all of the guidance forecast weakening, and the new forecast
follows suit in calling for Marty to become a depression by 72 hours
and a remnant low by 120 hours.  The remnant low forecast is
somewhat uncertain, as there is a chance that the shear may decrease
by 120 hours.

A tropical storm warning may still be required for portions of the
coast of Mexico later tonight.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 15.1N 102.9W   50 KT  60 MPH
 12H  28/0600Z 15.6N 102.6W   55 KT  65 MPH
 24H  28/1800Z 16.1N 102.2W   55 KT  65 MPH
 36H  29/0600Z 16.5N 101.8W   55 KT  65 MPH
 48H  29/1800Z 16.9N 101.9W   45 KT  50 MPH
 72H  30/1800Z 17.0N 103.0W   30 KT  35 MPH
 96H  01/1800Z 17.0N 104.5W   25 KT  30 MPH
120H  02/1800Z 17.5N 106.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven