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Tropical Storm Priscilla Forecast Discussion


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741 
WTPZ44 KNHC 201440
TCDEP4

Tropical Storm Priscilla Discussion Number   2
NWS National Hurricane Center Miami FL       EP192019
1000 AM CDT Sun Oct 20 2019

Deep convection, with some overshooting cloud tops to -90 deg C, has
continued to develop and expand since the previous advisory. Most of
the convective cloud mass has been displaced into the western
semicircle due to modest easterly to southeasterly vertical wind
shear. However, the cold cloud canopy has expanded eastward over the
center during the past couple of hours, suggesting that the cyclone
is becoming better organized and has also strengthened. The initial
intensity of 35 kt is based on earlier scatterometer wind data that
showed 32-33 kt in the southwestern quadrant, along with the much-
improved satellite signature since the time of the ASCAT passes. The
35-kt intensity is also supported by recent satellite intensity
estimates of T2.5/35 kt and T2.3/33 kt from TAFB and UW-CIMSS ADT,
respectively. Thus, the cyclone was upgraded to Tropical Storm
Priscilla at 1200 UTC.

Priscilla is moving a little west of due north or 355/6 kt. The
small cyclone is expected to move generally northward around the
western extent of a deep-layer ridge that is oriented east-to-west
across the Bay of Campeche and south-central Mexico. This slow
motion should bring the center of Priscilla inland over southwestern
Mexico late this afternoon or early evening. The latest NHC model
guidance is tightly packed around the previous advisory track, so no
significant changes to the previous track forecast were required.

Priscilla will be moving over SSTs in excess of 29 deg C and into an
upper-level environment of gradually decreasing shear, so some
additional slight strengthening will be possible before landfall
occurs in about 12 hours. However, the peak intensity likely will
not be much higher than 40 kt. After moving inland, Priscilla will
rapidly weaken and dissipate due to the rugged mountainous terrain
of southwestern Mexico.

The primary threat with Tropical Storm Priscilla will be heavy
rainfall, along with the potential for flash flooding and mudslides,
over portions of southwestern Mexico during the next day or two.


FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 18.1N 104.0W   35 KT  40 MPH
 12H  21/0000Z 19.0N 104.2W   35 KT  40 MPH...NEAR MEXICAN COAST
 24H  21/1200Z 19.7N 104.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 36H  22/0000Z...DISSIPATED INLAND

$$
Forecaster Stewart