Tropical Weather Discussion

axpz20 knhc 132209

Tropical weather discussion
NWS National Hurricane Center Miami FL
2205 UTC Thu Dec 13 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 
2030 UTC.

...Special features...

Gulf of Tehuantepec gale warning: a cold front forecast to enter 
the NW Gulf of Mexico this evening will initiate gale to strong 
gale force winds across the Gulf of Tehuantepec by Fri evening 
and is then expected to persist through the upcoming weekend and 
beyond. Computer model guidance suggests that this long lived 
gale event will last until Mon afternoon. Peak winds are 
forecast to be 40 kt on Sat as corresponding seas quickly 
building to near 18 ft. The first blast of strong northerly 
winds associated with this event is expected to start during 
Fri afternoon.

...Intertropical convergence zone/monsoon trough...

The monsoon trough extends from 09n75w to 03.5n78.5w to 08.5n85w 
to 05n102w. The ITCZ continues from 05n102w to 08.5n118w to 
10n134w to beyond 07n140w. Scattered moderate to strong 
convection is observed from 01.5n to 05.5n to the east of 85w, 
while scattered moderate convection is observed from 04.5n to 
07n between 92w and 102w. An upper level trough across far NW 
portions of the area is creating a large area of overcast middle 
and high level clouds, and scattered light to moderate elevated 
convection from 15n to 22n between 120w and 136w.


Offshore waters within 250 nm of Mexico... 

Over the open waters off Baja California, another pulse of NW 
swell is expected to reach Baja California norte and Guadalupe 
island tonight. This latest round of swell will propagate se and 
cause seas to build to between 7 and 11 ft for the offshore 
waters along the length of the Baja Peninsula by Fri afternoon. 
A cold front approaching 30n140w late tonight will introduce 
more long period NW swell to baja waters by Sun morning and 
maintain sea heights at 7-9 ft through Mon morning. Looking 
ahead, a much stronger cold front will reach Baja California 
norte by Mon night. Strong winds associated with this front 
could brush 30n as the front crosses 30n140w. Long period NW 
swell of 10-18 ft will enter the waters adjacent to Baja 
California norte during this time frame. Swell of this size and 
period will present hazard seas for mariners as well as cause 
very powerful and dangerous surf along the Pacific beaches.

Strong high pressure building over the Great Basin will support 
the development of fresh to strong winds over the Gulf of 
California between 25n and 29n this afternoon through Fri 
morning. Seas could approach 8 ft over the southern Gulf 
tonight. Winds and seas will subside through Sat as the high 
pressure shifts eastward.

Offshore waters within 250 nm of Central America, Colombia, and 
within 750 nm of Ecuador... 

Gulf of papagayo...strong gap winds have tapered off today but 
will return during the overnight and early morning hours Sat 
night, then persist through Mon night as high pressure builds 
north of the region. Seas are expected to Max out around 10 ft 
on sun.

Gulf of Panama...fresh northerly winds across and downstream of 
the Gulf have begun to back to the NW this afternoon and will 
slowly diminish through Sat.

Elsewhere, gentle to moderate winds will persist on either side 
of the monsoon trough through the remainder of the week, with 
seas remaining in the 4-6 ft range.

Remainder of the area... 

A large area of mixed seas persists over much of the North 
Pacific between 95w and 120w. This area consists of NE and E 
swell generated by recent Central American gap wind events, 
merging with longer period NW swell. Maximum combined sea 
heights in this area are 10 ft. This area of 8 ft seas will 
vanish by late tonight as these swell decay.

Farther west, a persistent surface trough extends from 08n139w 
to 16n134w. The gradient between this trough and high pressure 
north of the region is supporting strong trade winds from 15n to 
20n between 125w and 140w. Recent satellite-derived wave height 
data indicate seas as high as 13 ft. The high will weaken today 
ahead of an approaching cold front, allowing the trade winds to 
diminish by Fri morning.

A cold front will reach from 30n135w to 28n140w by early Fri, 
and be accompanied by a new round of NW swell of 12 to 15 ft. 
The front will dissipate later on Fri, with the swell subsiding 
as well. Elsewhere NW swell in excess of 8 ft will more or less 
dominate the waters west of 110w through sun. Very large NW 
swell, in excess of 20 ft, will enter NW portions of the 
forecast area early sun in conjunction with the arrival of a 
strong cold front. Seas of 12 ft or above could encompass almost 
all of the forecast waters N of 07n and W of 115w by Tue morning.



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