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TROPICAL STORM MARTY DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
1000 PM CDT TUE SEP 29 2015

After an unusually long convective burst that began around 1800 UTC,
the convective pattern of Marty has deteriorated significantly over
the past couple of hours. However, a 2306 UTC GPM microwave overpass
indicated that Marty still had a 60-70 percent closed low-level eye
with a diameter of 15 n mi. Based on the partial eye feature and a
Dvorak classification of T3.0/45 kt from TAFB, the initial
intensity is being maintained at 45 kt for this advisory.

Microwave satellite images indicate that Marty has essentially been
stationary since the previous advisory. However, as Marty's
low-level and mid-/upper-level circulations begin to decouple during
the next 12 hours or so due to increasing vertical wind shear, the
cyclone is forecast to begin moving slowly westward tonight and on
Wednesday under the influence of a weak low- to mid-level ridge
located over central Mexico. Although the spread in the track
guidance is fairly large, the models are in generally good agreement
on a slow westward to west-northwestward motion throughout the
forecast period. As a result, the official forecast track is similar
to the previous advisory track, and lies close to the consensus
models TVCE and GFEX.

Despite strong shear conditions, the recent convective burst has
been sustained by strong upper-level difluence created by
southwesterly flow over the northwestern portion of the Marty's
circulation and westerly flow over the southeastern portion of the
circulation. However, this favorable upper-level pattern is expected
to abate during the next 12 hours and be replaced by strong
southwesterly unidirectional flow, which should create very
unfavorable shear conditions across the cyclone. The result is that
Marty should steadily or even rapidly weaken, becoming a tropical
depression in about 24 hours, followed by degeneration into a
remnant low by 36-48 hours. The NHC intensity forecast follows the
weakening trend of the previous intensity forecast, and remains in
agreement with the LGEM statistical-dynamical intensity model.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0300Z 16.3N 101.2W   45 KT  50 MPH
 12H  30/1200Z 16.4N 101.8W   35 KT  40 MPH
 24H  01/0000Z 16.6N 102.8W   30 KT  35 MPH
 36H  01/1200Z 16.7N 104.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  02/0000Z 16.8N 105.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  03/0000Z 17.0N 107.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  04/0000Z 18.5N 109.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  05/0000Z...DISSIPATED

$$
Forecaster Stewart

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