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Tropical Storm Vicente Discussion Number   2
NWS National Hurricane Center Miami FL       EP232018
400 PM CDT Fri Oct 19 2018

Although tiny, the cyclone continues to display well-defined
convective banding.  The system's quick formation and small size
make it difficult to have high confidence in its current intensity,
and the various subjective and objective estimates range from
T1.8/28 kt from the ADT to T3.0/45 kt from SAB.  As a compromise,
the intensity is set at 35 kt, which is closest to the TAFB estimate
and the most recent SATCON number, and the depression is upgraded to
Tropical Storm Vicente.

As noted this morning, warm waters and low shear should induce
further strengthening during the next 48 hours.  On one hand, this
intensification could be more than what is being indicated by the
models, since small systems can have a tendency to gain strength
quickly.  On the other hand, Vicente will be interacting with a Gulf
of Tehuantepec gap wind event during the next 48 hours, and the
storm could end up ingesting some drier, more stable air into its
circulation.  The NHC intensity forecast favors the former scenario
and is a little above the guidance envelope for the first 2-3 days.
After day 3, an increase in shear, interaction with another possible
tropical cyclone to the west, and possible interaction with land
could all conspire to arrest the intensification trend, and
weakening is expected by the end of the forecast period.  It is also
possible that Vicente could dissipate before the end of the 5-day
period.  This scenario is reminiscent of, and has similarities to,
the interaction of Tropical Storm Ileana and Hurricane John back in
early August.

Vicente is moving very slowly northwestward, or 305/2 kt.  The
track models are indicating that the ongoing gap winds over the Gulf
of Tehuantepec may have a greater influence of Vicente than
previously thought, forcing the storm to turn west-southwestward in
the next 24-48 hours.  After 48 hours, Vicente should gradually
enter the flow between mid-level ridging over Mexico and low
pressure west of Mexico, causing it to turn back to the west and
northwest on days 3 through 5.  The new NHC track forecast is not
too different from the morning forecast during that period, and it's
closest to the paths shown by the GFS, HCCA, and FSSE guidance,
which would bring the center close to the coast of Mexico later in
the forecast period. There are considerable speed differences,
however, and the NHC forecast splits the difference between the fast
ECMWF solution and the slow GFS scenario.

Even though Vicente should begin to slowly pull away from the coast
tonight and on Saturday, 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  19/2100Z 13.3N  92.2W   35 KT  40 MPH
 12H  20/0600Z 13.6N  93.3W   45 KT  50 MPH
 24H  20/1800Z 13.3N  94.2W   50 KT  60 MPH
 36H  21/0600Z 12.9N  95.2W   55 KT  65 MPH
 48H  21/1800Z 12.7N  96.5W   55 KT  65 MPH
 72H  22/1800Z 13.7N  99.8W   55 KT  65 MPH
 96H  23/1800Z 16.5N 103.0W   55 KT  65 MPH
120H  24/1800Z 20.0N 106.0W   45 KT  50 MPH

$$
Forecaster Berg

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