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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 092205

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2151 UTC Sun Dec 9 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
2045 UTC.


Gulf of Tehuantepec Gale Warning: High pressure is pressing 
southward along the eastern slopes of the Sierra Madre Oriental 
mountains of Mexico. The large pressure difference between the 
high and lower pressure south of Mexico will result in an abrupt 
onset of strong to near gale force north to northeast winds, 
which will surge southward across the Isthmus of Tehuantepec and 
out over the Gulf of Tehuantepec. Strong winds have already begun
to affect the Gulf N of 14N. These winds will quickly increase 
to strong gale force this evening. Seas in the gale area are 
forecast to build to between 12 and 18 ft by late tonight. The 
strong gale force winds will continue through Tue, then diminish 
to minimal gale force Tue night. Winds will then quickly decrease
and become light by Wed evening as the strong high over the Gulf
weakens and shifts eastward. Swell from this event is forecast 
to propagate S and SW well away from the Gulf of Tehuantepec 
region, with the leading edge of the 8 ft seas expected to reach 
near 09N110W by late Tue night or Wed. Please refer to the 
Eastern Pacific High Seas Forecast under AWIPS/WMO headers 
HSFEP2/FZPN03 KNHC for more specific marine details.


The monsoon trough axis extends from low pres 1010 mb near 
06N74W to 05N83W to 05N90W. The ITCZ continues from 05N90W to
07N104W, then resumes from 10N113W to 09N123W to beyond 07N140W.
Scattered moderate and isolated strong convection is noted within
90 nm either side of a line from 05N118W to 08N131W. A surface
trough splits the ITCZ from 06N109W to 10N109W to 
14N109W. Scattered moderate and isolated strong convection is
seen from 11N to 14N between 105W and 110W. 



A 1027 mb high pressure area is centered west of northern Baja 
California Norte near 32N124W. Strong high pressure is currently
centered over the Great Basin as well. The pressure gradient 
between these high pressure areas and enhanced troughing across 
the Gulf of California is supporting fresh to strong NW winds 
across mainly southern half of the Gulf of California. Seas in 
this area are estimated to be as high as 5 ft. Looking ahead, 
strong high pressure building over the Great Basin well north of 
the area will support strong NW winds over mainly the northern 
Gulf of California Thu. 

Recent satellite-derived sea height data show most of the large,
long- period NW swell inundating the open waters over the past 
couple of days have subsided below 8 ft, with the exception of 
the area near the Revillagigedo Islands. A new group of NW swell 
in excess of 8 ft will reach the waters off the northern Baja 
California coast and near Guadalupe Island by late Mon, then 
spread east to cover most of the waters off the entire Baja 
California peninsula and the Revillagigedo Islands through Tue 
night, before subsiding below 8 ft through Wed.


Gulf of Papagayo...Winds will pulse to strong intensity during 
the overnight and early morning hours over the Gulf of Papagayo 
beginning tonight and through Wed night as high pressure shifting
eastward over the Gulf of Mexico builds southward toward the NW 
Caribbean Sea and Central America.

Elsewhere, gentle to moderate winds will persist on either side 
of a weakening monsoon trough and seas in the range of 4 to 6 ft.


A cold front extends from near 32N133W to 27N140W. Long-period 
NW swell is following in behind this front, and will bring seas
in excess of 8 ft over most of the area west of 120W through
early Tue. This will reinforce older, decaying NW swell 
lingering south of 20N, mixed with shorter period trade wind 
swell. High pressure building behind the front will support
generally fresh trade winds over the deep tropics west of 125W 
through mid week, with fresh to strong winds possible west of 
135W. Trade wind convergence along with an assist from divergent
flow aloft on the southeast side of a broad upper trough over 
Hawaii is supporting clusters of showers and thunderstorms along
the ITCZ, and this will persist sporadically through early in the

Wave model guidance suggests that a rather large area of 8 ft 
seas associated with mixed swell will exist Wed morning from 
about 03N to 13N between 94W and 110W as a result of long period 
northwest swell mixing with shorter period northeast swell that 
propagate downstream from the Gulf of Tehuantepec and to a 
smaller extent those induced by the Gulf of Papagayo strong 
pulsing northeast winds.