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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 150336

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Sat Dec 15 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 0000 UTC surface analysis and satellite imagery through 
0230 UTC.


Gulf of Tehuantepec Gale Warning: Strong northerly winds have 
increased to gale force across the Gulf of Tehuantepec north of 
14.5N in the past few hours, associated with a cold front 
crossing the central Gulf of Mexico this evening. Strong high 
pressure behind this front will produce a further increase in 
winds to strong gale force winds during the next few hours and 
continue through early Sun. Computer model guidance suggests 
that these gales will continue through the weekend and will last 
until Mon afternoon. Peak winds are forecast to be around 40 kt 
on Sat as corresponding seas quickly build to near 18 ft. 


The monsoon trough extends from 09N72W TO 06N82W TO 06N104W. The 
ITCZ continues from 06N104W TO 09N131W to beyond 08N140W. 
Scattered moderate isolated strong convection is noted within 
150 nm S of the trough between 77W and 86W, and from 05N to 
11.5N between 125W and 137W. 



Weak high pressure ridging SE from 32N122W to near 28N116W is 
maintaining light to gentle breezes across the Pacific waters 
off Baja California. Fresh NW flow continues over the Gulf of 
California between 24N and 29N. Meanwhile the next pulse of long 
period NW swell has entered the area from the west, and is 
moving S of Baja California Sur this evening. NW swell will 
dominate the offshore waters off the entire Baja California 
coast through the Revillagigedo Islands with seas building up to 
9 ft tonight, followed by reinforcing NW swell through Sun. 

Looking ahead, a cold front will reach the northern coast of 
Baja California by Mon night, accompanied by large reinforcing 
NW swell, bringing seas of 12 to 18 ft to all of the offshore 
zones of Baja California and into the Revillagigedo Islands by 
late Tue. Swell of this size and period will present hazardous 
seas for mariners, cause very powerful and dangerous surf along 
the Pacific reefs and beaches, and likely produce areas of 
modest coastal flooding and beach erosion.

A mid to upper-level disturbance is approaching the area from 
the west. This disturbance is currently interacting with a 
surface trough extending from 09N133W TO 17N127W. The 
disturbance is producing scattered moderate convection from 14N 
to 23N between 117W and 127W, and is expected to shift NE 
through the weekend. This may bring a few showers to the central 
and southern portions of the Baja California Peninsula and Gulf 
of California late tonight through Sun.


Gulf of Papagayo...Fresh gap winds will pulse to around 20 kt 
tonight before ramping back up to between fresh and strong 
during the overnight and early morning hours Sat night. These 
conditions will then persist through Mon night as high pressure 
builds north of the region. Seas are expected to max out near 10 
ft Sun morning.

Gulf of Panama...Fresh northerly winds across and downstream of 
the Gulf will slowly diminish through Sat, then become fresh 
from the north Sat night through Tue.

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.


Weak ridging prevails across the NE waters off of Baja 
California. A persistent surface trough extends from 09N133W TO 
17N127W. Afternoon scatterometer data indicated fresh to strong 
winds on the W side of the trough between 11N and 19N, and east 
of the trough to 125W from 16N to 19N. The high pressure ridge 
to the N will weaken through tonight ahead of an approaching 
cold front, allowing the winds to diminish to between moderate 
and fresh by Sat morning.

A weakening cold front crossing the NW portion of the discussion 
area extends from 30N132W TO 25.5N140W, and is introducing a new 
round of NW swell with seas of 11 to 15 ft following the front. 
The front will slow forward motion then dissipate through Sat, 
with the swell propagating ahead of the front and slowly 
subsiding. Elsewhere NW swell in excess of 8 ft will more or 
less dominate the waters west of 110W through Sun. A stronger 
cold front will usher in very large NW swell, in excess of 20 
ft, which will enter NW portions of the forecast area early Sun. 
Seas of 12 ft or higher could encompass almost all of the 
forecast waters N of 07N and W of 115W by Tue morning.