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TROPICAL STORM MARTY DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
400 PM CDT TUE SEP 29 2015

Analyses from CIMSS at the University of Wisconsin show that the
westerly shear over Marty has increased to 35 kt, which is
disrupting the structure of the cyclone.  Satellite imagery and
data from the Mexican radar at Acapulco indicate a new burst of
convection in curved bands has developed to the northeast of the
center. However, so far this burst is smaller than the previous
one.  The initial intensity is decreased to 45 kt in agreement
with satellite intensity estimates from TAFB and SAB.

After moving a little to the east earlier today, the latest
satellite and radar data suggest that the center is now drifting
northward with an initial motion of 000/2.  The mid- to upper-level
trough north of the system is weakening and splitting, with an
upper-level low developing northwest of Marty and a mid-level ridge
developing north of the storm.  This evolution should result in
Marty beginning a west-northwestward to westward motion during the
next 12-24 hours, and all of the track guidance supports this
scenario.  The new forecast track is similar to, but faster than the
previous track.  However, it is again slower than the model
consensus.

Continued moderate to strong shear should cause maintain steady to
rapid weakening.  The new intensity forecast, which is in best
agreement with the LGEM model, is an update of the previous forecast
and calls for Marty to weaken to a tropical depression in 24 hours
and then degenerate into a remnant low by 36 hours.  It should be
noted that this forecast again lies on the upper edge of the
intensity guidance envelope, so Marty could weaken faster than
currently forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 16.3N 101.2W   45 KT  50 MPH
 12H  30/0600Z 16.4N 101.5W   35 KT  40 MPH
 24H  30/1800Z 16.6N 102.4W   30 KT  35 MPH
 36H  01/0600Z 16.7N 103.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  01/1800Z 16.8N 104.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  02/1800Z 17.0N 106.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  03/1800Z 17.5N 108.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  04/1800Z...DISSIPATED

$$
Forecaster Beven

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