Tropical Weather Discussion
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296
AXPZ20 KNHC 182104
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2104 UTC Thu Jan 18 2018

Tropical Weather Discussion for the eastern Pacific Ocean from
the Equator to 32N, east of 140W. The following information is
based on satellite imagery, weather observations, radar, and
meteorological analysis.

Based on 1800 UTC surface analysis and satellite imagery through
2100 UTC.

...SPECIAL FEATURES...

Gulf of Tehuantepec Gale Warning: Strong high pressure continues
to extend southward across eastern Mexico and the western Gulf
of Mexico while a surface trough lingers just to the E in the
western Gulf of Mexico, resulting in a very tight pressure
gradient in the area. Winds are expected to gradually diminish
below gale force by Friday afternoon as the pressure gradient
weakens. The resultant plume of northerly swell will continue to
propagate well southward of the Gulf of Tehuantepec waters,
mixing with long period NW swell to produce seas in excess of 8
ft. Maximum seas through today will remain around 14 to 17 ft
near the strongest winds, gradually subsiding by the end of the
week as the winds diminish. Another gale force wind event will be
possible next week.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

A surface trough axis extends from 09N76W to 05N86W to 05N104W.
The intertropical convergence zone axis extends from 05N104W to
07N114W to 06N125W to 07N140W. Scattered moderate convection is
within 90 nm N of the trough between 97W and 103W, within 180 nm
N of the trough between 108W and 117W, and within an area
bounded by 17N127W to 08N118W to 06N127W to 12N137W to 17N127W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

Please see the special features section for information about
the ongoing gale warning in the offshore waters of the Gulf of
Tehuantepec.

In the Gulf of California, light to moderate NW flow is expected
across across the entire gulf waters through Friday afternoon.
Winds will become southerly Friday evening ahead of an
approaching cold front, increasing to fresh to strong in the
northern gulf Friday night, then shifting to NW to N behind the
front, while briefly increasing to near gale force behind the
front. The front will gradually become ill defined as it moves
southward through the gulf during the day Saturday with mainly
moderate to fresh northerly flow in its wake for the end of the
weekend. The ill defined remnants of the front are expected to
push S to the entrance of the gulf by Sunday afternoon when the
pressure gradient will begin to tighten across the area, leading
to fresh to strong winds across the full length of the gulf
Sunday evening and night.

Elsewhere across the offshore waters of Mexico, large NW swell
continues to propagate SE across the waters, with seas of 8-11
ft prevailing, except 5-8 ft within 60-120 nm of shore between
97W and 104W. This large swell continues to generate high and
powerful surf along the coasts and outer reefs of the Baja
California peninsula and mainland Mexico, which will continue
this evening, with coastal flooding possible. Another pulse of
NW swell will reach the offshore waters off Baja California Norte
tonight. Seas will peak near 13-15 ft by Friday, while seas of
12 ft or greater will spread across the offshore waters off the
entire length of the Baja Peninsula through the upcoming weekend.
NW winds offshore of Baja California Norte will temporarily
increase to fresh to strong by early Saturday as the pressure
gradient tightens.

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...

Fresh NE gap winds prevailing across the regional waters between
Papagayo and Tehuantepec will pulse to strong each night and
early morning across the Gulf of Papagayo and other typical gap
wind areas through Saturday morning, diminishing thereafter.
Winds will peak at near gale force offshore of Papagayo early
Friday. Elsewhere, mainly light to gentle offshore winds will
prevail N of 09N, with light to gentle southerly flow S of 09N.
NW swell originating from the gale wind event in the Gulf of
Tehuantepec along with longer period NW swell will arrive across
the area waters Thursday and Friday, building seas offshore to
5-7 ft.

REMAINDER OF THE AREA...

Large, long period NW swell continues to propagate SE across the
forecast waters, with seas of 8 to 12 ft across the waters W of
90W-95W. A weakening cold front from 30N132W to 25N140W has
ushered in a reinforcing set of NW swell with seas up to 13-16
ft N of and along 30N. The front will get reinforced as high
pressure builds in its wake tonight with N-NE winds behind it
increasing to fresh to strong. The front will then gradually wash
out during the upcoming weekend as it approaches southern
California and NW Mexico, while the high behind it supports fresh
to strong trades across the majority of the waters N of 10N and
W of 110W.

$$
Lewitsky




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