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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 180914

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
914 UTC Tue Dec 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 0600 UTC surface analysis and satellite imagery through
0900 UTC.


Gulf of Tehuantepec Gale Warning: A scatterometer satellite pass
from 0318 UTC showed gap winds were still reaching 35 kt into 
the Gulf of Tehuantepec, between high pressure north of the area
and relatively lower pressure over the eastern Pacific. The high
pressure is moving eastward, allowing gap winds into the Gulf of
Tehuantepec to finally diminish below gale force early this
morning. Winds will diminish further to below 20 kt by late
today, as seas subside from 11 to ft less than 8 ft. Light to
gentle breezes will persist into Thu, followed by another gale
event by late Thu as a strong cold front pushes across the Gulf
of Mexico north of the area. Strong gales with seas reaching as
high as 18 ft will persist through late Fri and early Sat before
gradually diminishing. Please refer to the latest high seas 
forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more 
specific marine related details. 


No monsoon trough is observed. A weak trough extends from 06N95W
to 07N120W to 09N140W. Scattered moderate convection is noted
from 05N to 08N between 108W and 113W.



A trough reaching from 32N118W to 27N127W is sliding eastward 
across the northern waters toward Baja California Norte. The 
front will become diffuse through early today, and be followed by
moderate high pressure and freshening northerly winds across the
offshore waters. This pattern will prevail through early Wed 
before the ridge begins to weaken. Also accompanying the front is
very large NW swell, with the leading edge of 12 ft seas or 
greater impacting the northern coast of Baja California Norte. 
Seas of 12 ft or greater in NW swell will reach the length of the
coast of Baja California Sur and the Revillagigedo Islands by 
this afternoon. Swell of this size and period will produce 
hazardous seas for mariners, and create very large and powerful 
surf along the Pacific reefs and beaches. This high surf will 
also produce coastal flooding and beach erosion in many exposed 
locations from southern California to western Mexico. 

This swell will decay to 8 to 10 ft by late Wed, just ahead of 
another round of NW swell to 12 ft reaching Guadalupe Island and 
the northern coast of Baja California by late Thu. This swell 
will also decay below 12 ft rapidly, leaving 8 to 10 ft NW swell 
in place for the Mexican open waters west of 105W through Sat.

Across the Gulf of California, strong high pressure will build 
over the Great Basin by Wed. The high will support fresh to 
strong winds across the northern and central Gulf Wed through 
Thu, while seas build to 5- 8 ft.


The pressure gradient between a wedge of high pressure extending
from the Caribbean over Central America and lower pressure over 
the eastern Pacific will continue to support fresh to strong gap 
winds across Papagayo and other typical gap wind zones of 
central America until tonight, then winds will slacken as the 
high over the Caribbean shifts E.

Farther south, fresh to strong trade winds across the southwest 
Caribbean will support fresh gap winds over the Gulf of Panama 
through tonight. Winds during this time frame could possibly 
pulse to strong off the Azuero Peninsula.

Elsewhere, gentle to moderate winds will persist on either side 
of the monsoon trough through early next week, as seas remain in 
the 4 to 6 ft range.


An upper-level trough extending from northern Baja California
Norte to 10N135W is supporting a persistent surface trough along
roughly 132W from 06N to 17N. The combination of lower level 
trade wind convergence and divergence aloft on the east side of 
the upper trough is supporting scattered convection from 13N to
16N between 113W and 117W.

Farther N, a 1025 mb high is centered along 31N130W, behind the 
trough approaching Baja California Norte. This high will meander
about this area for the next few days and maintain a modest 
pressure gradient to the south and southwest, to produce fresh to
locally strong NE to E tradewinds between 10N and 20N to the W 
of 110W. Large NW swell moving through this area will produce 
rough seas of 10-15 ft today before seas subside very slowly 
through Thu.

An area of confused seas running 8 to 10 ft lingers in the area 
from 02N to 15N between 93W and 112W. The seas in this area are 
primarily a mix of NW swell with shorter period NE and E swell 
from ongoing Mexican and Central American gap wind events. This 
area will gradually diminish to 8 to 9 ft west of 100W by mid 
week in predominantly NW swell as it merges with the larger area 
of NW swell approaching from the west.