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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 170844

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
845 UTC Mon Dec 17 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: The tight pressure gradient 
over southeastern Mexico resulting from the combination of high 
pressure over northeast Mexico and lower pressure south of 
the region continues to produce gale force northerly winds to 
around 40 kt across the Gulf of Tehuantepec and downstream to 
near 14N95W, where seas are near 14 ft. Gap winds will diminish 
just below gale force late today as the strong high pressure 
over Mexico shifts eastward and weakens. Seas with this event 
will subside to 9 to 13 ft today and to less than 8 ft on Tue as
the northerly winds diminish to 20 kt or less. Looking ahead, 
another gale event is expected by late Thu as a strong cold front
moves into southern Mexico. Please refer to the latest high seas
forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more 
specific marine related details. 


No significant monsoon trough was observed. The ITCZ extends from
05N90W to 08N125W to 06N140W. Scattered moderate convection was
noted from 06N to 08N between 123W and 128W.



At the surface, a weak ridge will prevail over the area through 
Mon morning to maintain light to gentle breezes across the area 
waters. Northwest swell with seas 8 to 10 ft will dominate the 
offshore waters of Baja California through early morning before 
briefly subsiding to 6 to 8 ft through around noon today.

A weak cold front will move eastward into the area by this 
afternoon, then will become diffuse. The front will 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 
will be a new pulse of large NW swell, with the leading edge of 
12 ft seas or greater reaching the northern coast of Baja 
California Norte and Guadalupe Island by late morning. The long 
period NW swell will bring heights of 12 to 16 ft across most of 
the waters off Baja California and through the Revillagigedo 
Islands. 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. 

The swell will decay below 12 ft through Wed, ahead of a smaller
reinforcing group of swell bringing seas again to 12 ft to Baja 
California Norte Thu. Elsewhere seas in excess of 8 ft will 
persist in Mexican open waters west of 105W through the week. 

Across the Gulf of California, strong high pressure north of 
region is supporting moderate to fresh breezes across the south 
half of the basin this morning, with little change expected 
through Tue. Strong high pressure will build north of the area by
Wed, and will support fresh to strong winds across the northern 
and central Gulf, while seas build to 5-8 ft.


A scatterometer pass from 0000 UTC indicate fresh to strong gap
winds across the Gulf of Papagayo and Gulf of Fonseca. A tight
pressure gradient between a wedge of high pressure through
Central America and relatively lower pressure farther south will
support s persistent fresh to strong gap winds across Papagayo
into mid week.

The same scatterometer pass also indicated smaller areas of 
fresh to strong offshore winds along the coast of western El 
Salvador and eastern Guatemala, assisted in part by low pressure 
over the northwest Caribbean of the coast of Honduras. The low is
expected to weaken through today, allowing the cross-isthmus 
flow will diminish. 

Farther south, fresh to strong trade winds across the southwest
Caribbean are supporting fresh gap winds into the Gulf of Panama,
possibly pulsing to strong winds 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 trough from 32N130W to 10N140W is becoming a little more
amplified and is supporting a persistent surface trough along
roughly 131W from 08N to 16N. The combination of lower level
trade wind convergence and divergence aloft on the east side of
the upper trough is supporting scattered convection along the
intertropical convergence zone between 120W and 130W. A
scatterometer satellite pass from 0520 UTC showed strong trade
winds along the ITCZ in this area as well. 

Farther north, a weakening cold front analyzed from 31N125W to 
27N140W is expected to become diffuse as it moves eastward
toward Baja California through tonight. A new round of long
period NW swell is outrunning the front eastward, with the
leading edge of 12 ft seas reaching from 31N122W to 16N140W. An
altimeter satellite pass from 03 UTC showed seas to 22 ft near
30N133W. The NW swell will continue to move eastward, with 12 ft
seas dominating most of the area west of 120W and north of 05N by
late Tue. 

A pair of altimeter pass from around 0330 UTC and 0430 UTC 
showed confused seas 8 to 10 ft in an area probably from 03N to 
14N between 92W and 113W, primarily in a mix of NW swell with 
shorter period NE and E swell from ongoing Mexican and Central 
American gap wind events. This will gradually diminish to 8 to 9
ft west of 100W by mid week in predominantly NW swell.