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Tropical Storm VICENTE


Tropical Storm Vicente Discussion Number   4
NWS National Hurricane Center Miami FL       EP232018
400 AM CDT Sat Oct 20 2018

Radar data from Guatemala indicate that Vicente remains a very small
but well-defined tropical cyclone, which has occasionally exhibited
an eye-like feature. However, convection has waned during the past
few hours, so it is difficult to accurately ascertain the intensity
of such a tiny storm since small systems like this can spin up and
spin down very quickly owing to minor convective fluctuations. For
now, it is assumed that Vicente is still a tropical storm based on
satellite intensity estimates of T2.5/35 kt from TAFB and SAB, and
41 kt from UW-CIMSS SATCON; the most recent ADT value, however, was
T2.2/32 kt.

The initial motion estimate is 290/06 kt. Over the last 18 hours, it
appears that Vicente's track has been doing some coastal hugging.
That being said, the tropical storm is expected to turn more
westward during the next 12 h and emerge over the open Gulf of
Tehuantepec where a modest gap wind event is forecast to turn the
cyclone southwestward by this evening. The latest 00Z model guidance
is surprisingly in very good agreement on the development of this
unusual track scenario. By 36-48 hours, a gradual turn toward the
west is expected, followed by a motion toward the northwest on days
3-5 as the small cyclone rounds the southwestern periphery of a
deep-layer ridge located over the Gulf of Mexico and central Mexico.
Assuming Vicente survives the next 96 hours, on day 5 the tropical
cyclone is expected to come under the influence of the new and much
larger Tropical Depression 24-E -- currently located about 700 nmi
to the west -- and possibly become absorbed or forced inland over
southwestern Mexico by that system. The new NHC forecast was nudged
a little to the west at most forecast times, closer to the HCCA and
FSSE corrected consensus models.

Vertical shear is forecast to be less than 10 kt and the mid-level
moisture is expected to be high with humidity values of more than 75
percent for the next 36 hours. This should allow for some gradual
strengthening to occur during that time despite Vicente's proximity
to land. By 48 hours and beyond, however, northerly shear is
expected to increase across the small cyclone, which should act to
cap the intensification process and induce some gradual weakening
by 96h. On day 5, the shear is forecast to exceed 20 kt, due in
large part to the expected strong outflow from a strengthening
TD-24E, resulting in significant weakening or even dissipation of
Vicente. The official intensity forecast is similar to but slightly
below the previous forecast, and lies close to an average of the
HCCA, FSSE, and IVCN consensus models.

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
southeastern Mexico during the next few days.


INIT  20/0900Z 14.0N  93.1W   35 KT  40 MPH
 12H  20/1800Z 14.1N  93.9W   35 KT  40 MPH
 24H  21/0600Z 13.5N  95.3W   40 KT  45 MPH
 36H  21/1800Z 12.9N  97.1W   40 KT  45 MPH
 48H  22/0600Z 13.1N  98.7W   45 KT  50 MPH
 72H  23/0600Z 15.2N 101.9W   50 KT  60 MPH
 96H  24/0600Z 18.3N 104.9W   50 KT  60 MPH
120H  25/0600Z 21.8N 108.3W   35 KT  40 MPH

Forecaster Stewart