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TROPICAL STORM MARTY DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
1000 PM CDT SAT SEP 26 2015

The cyclone has become better organized during the past several
hours with a large burst of convection recently trying to form a
central dense overcast.  In addition, the latest microwave images
show some structure to the inner core, along with more pronounced
banding features south of the center.  On the basis of the increased
organization and the latest Dvorak estimate from TAFB, the initial
wind speed is set to 35 kt.

Marty is now moving northward at about 4 kt.  A turn to the
north-northeast is forecast on Sunday due to the storm moving around
the western side of a weak mid-level ridge over the far eastern
Pacific west of Central America.  While Marty will get close to
being caught by a trough over Mexico, most of the guidance suggest
that the cyclone will be left behind in a couple of days southwest
of the coast of Mexico due to the trough moving away.  Marty would
then drift west-northwestward in the low-level flow as a weaker
cyclone. The NHC forecast has shifted eastward in the first couple
of days, then westward at longer range with more model guidance
showing the solution where the cyclone is left behind.  This is an
uncertain forecast, however, and it wouldn't take much of a
deviation for stronger winds to approach the coast.  A tropical
storm watch could be issued for a portion of the coast of Mexico on
Sunday morning.

Marty is currently in an environment of light wind shear, high mid-
level moisture and very warm waters.  These favorable conditions
should last for the next 24-36 hours and promote intensification
during that time.  While none of the deterministic guidance shows
rapid intensification, the SHIPS-RI index shows about a 70 percent
chance of a 25-kt increase in the first 24 hours.  The intensity
forecast is set at the upper end of the guidance, about 5 kt above
the previous prediction through 36 hours.  After that time, almost
all of the global models show a significant increase in
southwesterly shear, which should cause Marty to weaken and probably
dissipate by day 5.  The official forecast is very close to the
previous one and the intensity consensus after 72 hours.

FORECAST POSITIONS AND MAX WINDS

INIT  27/0300Z 13.6N 103.0W   35 KT  40 MPH
 12H  27/1200Z 14.2N 102.8W   45 KT  50 MPH
 24H  28/0000Z 14.9N 102.6W   55 KT  65 MPH
 36H  28/1200Z 15.4N 102.3W   60 KT  70 MPH
 48H  29/0000Z 15.8N 102.0W   55 KT  65 MPH
 72H  30/0000Z 16.0N 102.0W   45 KT  50 MPH
 96H  01/0000Z 16.2N 102.3W   30 KT  35 MPH
120H  02/0000Z 16.5N 103.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Blake

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