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Tropical Storm Vicente Discussion Number   3
NWS National Hurricane Center Miami FL       EP232018
1000 PM CDT Fri Oct 19 2018

Radar imagery from Guatemala has been extremely helpful in tracking
the center of Vicente, especially after sunset.  The low-level
center of the small tropical storm appears to have accelerated
northwestward during the past couple of hours, away from its rapidly
decaying central dense overcast, and is now almost entirely
exposed. Analysis from UW-CIMSS indicates that 10-15 knots of
northwesterly shear is currently affecting Vicente, and this appears
to have been enough to significantly disrupt the organization of the
cyclone, probably due to its small size.  The initial intensity has
been held at 35 kt based on objective and subjective satellite
estimates at 00Z, but given the tiny size of Vicente and its
large swings in organization since early this morning, its unclear
how representative these estimates are of the true maximum winds.

Vicente is now moving west-northwestward, or 300/3 kt, and all of
the guidance indicates that it will turn westward overnight.  After
that time, a Gulf of Tehuantepec gap wind event will likely cause
the cyclone to turn southwestward, especially if Vicente remains
weak and shallow.  A few models even indicate the tropical storm
could dissipate entirely as it interacts with these winds. Assuming
the cyclone makes it past the Gulf of Tehuantepec intact, Vicente
should turn back toward the west-northwest or northwest after about
48 h as it gets steered by the flow between a mid-level ridge over
Mexico and another tropical cyclone that will likely develop off the
coast of Mexico by that time.  The NHC forecast has been shifted a
little to the west at most forecast times, closer to the HCCA and
FSSE aids, but is generally similar to the previous advisory.

Due in part to the rapid decline in Vicente's organization this
evening, the intensity forecast has been adjusted lower at most
forecast hours for the first 48 h of the forecast, but is still
generally higher than the model consensus. Most of the intensity
guidance still calls for intensification, especially between 36 h
and 72 h, when Vicente should be past the Gulf of Tehuantepec, and
the shear should remain generally low. By the end of the forecast
period, the global models indicate that Vicente will interact with a
much larger tropical cyclone to its west, which should cause Vicente
to weaken and possibly dissipate, though a 120 h point is still
carried in this forecast for continuity purposes.

Vicente should begin to slowly pull away from the coast overnight
and on Saturday, however, heavy rainfall, with possible
life-threatening flash flooding, is expected over portions of El
Salvador, Guatemala, and southeastern Mexico during the next few
days.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 13.7N  92.5W   35 KT  40 MPH
 12H  20/1200Z 13.7N  93.3W   40 KT  45 MPH
 24H  21/0000Z 13.3N  94.3W   45 KT  50 MPH
 36H  21/1200Z 12.5N  95.7W   45 KT  50 MPH
 48H  22/0000Z 12.3N  97.4W   45 KT  50 MPH
 72H  23/0000Z 13.8N 100.8W   55 KT  65 MPH
 96H  24/0000Z 17.0N 104.0W   50 KT  60 MPH
120H  25/0000Z 20.5N 107.5W   40 KT  45 MPH

$$
Forecaster Zelinsky

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