297 
AXPZ20 KNHC 310327
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Thu Dec 31 2020

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
0300 UTC.

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

The monsoon trough axis extends from 09N79W to 10N86W to 07N90W.
The ITCZ continues from 07N90W to 05N100W and to 07N125W to
07N135W to 06N140W. Scattered moderate to isolated strong 
convection is observed from 06N08N between 130W and 135W. 

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

A sharp mid to upper level trough that moved eastward over the
region yesterday is now becoming a cut off low over north central
Mexico. Associated deep low pressure at the surface over north
central Mexico along with relatively higher pressure north of the
area in the Great Basin and over the eastern Pacific is resulting
in near gale force NW winds across the Gulf of California. Seas
are estimated to be 10 ft over portions of the central and 
southern where the fetch is long enough to support developed
seas. A scatterometer satellite pass from around 17 UTC captured
NW winds to 25 kt in the far northern Gulf of California, and
winds are assumed to be slight stronger to near gale force 
farther south where the subtropical ridge axis extends across the
eastern Pacific to the south of Los Cabos. 

The ridging will weaken as another mid to upper level trough is 
moving onshore over the west coast of the US. This will allow winds
and seas to diminish across the central and southern Gulf of 
California through Thu morning. Low pressure may deepen over the
the northern Gulf of California however, where NW winds to 20 to
25 kt may persist Thu night into Fri. Fresh to strong NW winds
accompanied by reinforcing NW swell to 13 ft will reach the 
waters of Baja California Norte through late Thu. These winds 
will diminish through Thu night, but the NW swell will persist 
into early next week. Another round of large NW swell will reach 
Guadalupe Island by Mon night. These successive groups of 
reinforcing NW swell will maintain combined seas in excess of 8 
ft across the open Mexican offshore waters west of 110W through 
the early part of the week.

Farther south, moderate S to SW winds in the Gulf of Tehuantepec
may increase slightly by late Thu as low pressure moves into the
western Gulf of Mexico. The next round of gap winds to gale force
may start late Sat, as a cold front associated with the low
pressure sweeps across the western Gulf of Mexico. These gap wind
pulses will gradually diminish through the early part of next
week as the high pressure behind the front weakens and shifts
east.

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

Gentle to moderate winds and slight to moderate seas persist
across the region. The next round of fresh to fresh gap winds
through the Gulf of Papagayo region is possible by late Sat into
early Sun. Elsewhere, gentle to moderate winds along with slight
to moderate wave heights due to a southwest swell will change 
little over the Central American and equatorial waters through 
Sun night.

REMAINDER OF THE AREA...

A 1030 mb high center is analyzed just north of the area at 
32N133W, with a ridge stretching southeastward to the 
Revillagigedo Islands. Earlier scatterometer satellite data 
indicated that the pressure gradient resulting from the 
interaction between the ridge and the ITCZ to the south is 
producing fresh northeast to east trades over the deep tropics 
west of 120W, with a pocket of fresh to strong trades present 
from 15N to 25N west of 130W. The trades will expand eastward to
near 120W overnight as the ridge strengthens. Earlier altimeter 
passes showed wave heights in the range of 8-11 ft north of 
about 05N and west of 110W likely due to the combination of 
northeast wind waves with long- period northwest swell 
propagating through this part of the discussion area.

The ridge will weaken Thu through Fri night while it shifts 
east-southeastward ahead of an approaching cold front, allowing 
for northeast trades to diminish back to moderate to fresh 
speeds. Maximum wave heights will be about 10 or 11 ft, and wave 
heights of 8 ft or greater will remain west of 110W and north of 
04N through Fri. The cold front is forecast to become stationary 
near 30N140W by late Fri, but a reinforcing set of northwest will
accompany the front with wave heights 12 ft or greater covering 
the waters northwest of a line from Baja California Norte to 
12N140W by Sat night through early next week. 

$$
Christensen