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Eastern North Pacific Tropical Weather Discussion



000
AXPZ20 KNHC 130340
TWDEP 

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

...SPECIAL FEATURES...

...Gulf of Tehuantepec Gale Warning... 

Winds continue to diminish this evening across the Gulf as high 
pressure over the Gulf of Mexico weakens and shifts east. Light 
to gentle winds are expected tonight through Thu night. Seas of 
8 to 9 ft within 250 nm of the coast of Oaxaca and Chiapas will 
subside below 8 ft through tonight as well. The improved marine 
conditions will be short-lived, however, as a cold front 
forecast to move into the Gulf of Mexico on Thu is expected to 
initiate another strong gale force wind event late Fri through 
Sun.  

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

The monsoon trough extends from 09.5N72W TO 09.5N83W TO 05N100W. 
The ITCZ extends from 05N100W TO 09N117W TO 10N130W to beyond 
08N140W. No significant convection is observed.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO... 

Over open waters off the Baja California coast, lingering long 
period NW swell along the length of the coast and in the 
Revillagigedo Islands will decay below 8 ft through tonight, 
just ahead of another pulse of NW swell, expected to reach the 
northern section of Baja California Norte and Guadalupe Island 
by Thu night. This new swell will reclaim the territory vacated 
by the previous swell through early Sat with significant wave 
heights reaching 10 ft. 

Strong high pressure building over the Great Basin will support 
a push of fresh to strong winds into the northern Gulf of by 
early Thu, eventually spreading across most of the Gulf through 
Fri with seas approaching 8 ft over the southern Gulf where the 
fetch would be longest. Winds and seas will subside through Sat 
as the high pressure shifts eastward into the Central Plains.

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND 
WITHIN 750 NM OF ECUADOR... 

Gulf of Papagayo...Overnight gap winds have been active for the 
past several nights, but will only reach 20 kt tonight and Fri 
night as high pressure north of the area shifts eastward. Fresh 
to strong gap winds with seas to 9 ft will resume during 
overnight and early morning hours Sat night as the next system 
builds north of the region.

Gulf of Panama...Fresh northerly winds will pulse to around 20 
kt overnight and build downstream seas to 5-7 ft through Thu 
morning before winds back to the NW and 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 in the 4-6 ft range.

REMAINDER OF THE AREA... 

A large area of confused seas persists over much of the north 
Pacific east of 110W, consisting of primarily NE and E swell 
mixed from gap winds, merging with longer period NW swell. 
Combined sea heights in this area are still reaching up to 11 
ft, but will be subsiding below 8 ft through Thu night.

Farther west, a surface trough continues from 08N132W TO 
13N128W. The pressure gradient between this trough and 1029 mb 
high pressure north of the region centered along the subtropical 
ridge near 32N139W is supporting generally fresh trade winds 
from the ITCZ to 20N, west of 115W. Scatterometer passes from 18 
UTC indicated fresh to strong NE winds within 180 nm west of the 
trough. Seas are 8 to 12 ft in this area, in a mix of local seas 
from the trade winds and longer period NW swell. The high 
pressure will weaken through Thu ahead of a cold front 
approaching from the west, allowing the trade winds to diminish.

The next 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 as it moves east to the north of 
20N, 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. Looking ahead, a more substantial group of NW 
well will move into the area by early Sun.

$$
Stripling