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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 180929

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Mon Oct 18 2021

Tropical Weather Discussion for the eastern Pacific Ocean from
03.4S to 30N, east of 120W including the Gulf of California, and
from the Equator to 30N, between 120W and 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
0920 UTC.


Gulf of Tehuantepec Gale Warning: High pressure continues to
build across the Gulf of Mexico behind a frontal boundary that 
extends from Key Largo to the eastern Bay of Campeche. Fresh to 
near gale force winds in the Bay of Campeche continue to funnel 
across the Chivela Pass this morning, thus supporting northerly 
strong to gale force winds in the Tehuantepec region. Seas with 
these winds range between 8 to 11 ft. The front will move east 
of the Gulf of Mexico later this morning. This will result in a 
weaker pressure gradient and winds diminishing below gale force 
in Tehuantepec. Please see the latest High Seas Forecast at for more details. 


A tropical wave extends north of 02N to Guatemala with axis near
90W, moving westward at 10-15 kt. Scattered moderate convection
is N of 06N between 83W and 93W. 

A tropical wave extends from 03N to 15N with axis near 104W, 
moving westward at 10-15 kt. Scattered moderate convection is 
from 06N to 16N between 96W and 102W.

A tropical wave extends from 04N to 16N with axis near 121W, 
moving westward at 15 kt. Scattered moderate convection is from 
06N to 13N between 116W and 129W.


The monsoon trough axis extends from 08N79W to 11N104W to a 1012
mb low near 11N110W to 11N140W. Aside from the convection 
associated with the tropical waves discussed in the section 
above, scattered moderate convection is N of 02N E of 82W, from 
08N to 12N between 108W and 114W, and from 07N to 15N W of 135W.


See the Special Features section above for more information on 
the ongoing Gale Warning for the Gulf of Tehuantepec.

A weak pressure gradient across the region is maintaining gentle
to locally moderate NW winds over the Baja California peninsula
offshore waters and light to gentle variable winds across the
southern half of the Gulf of California and the SW Mexico
offshore waters outside of the Tehuantepec area. Seas are 3 to 5
ft in mixed NW and SW swell. Over the northern Gulf of 
California, a surface trough is supporting fresh to locally strong
SW to W winds with seas to 3 ft. Otherwise, showers and tstms 
are across the offshore waters of Oaxaca and Chiapas associated 
with the frontal boundary N of the area and a tropical wave
approaching from the E.

For the forecast, gentle to moderate winds will persist into mid
week and the swell will subisde by Tue. By Tue night, new NW 
long period swell will start to move into the waters off Baja 
California Norte, building seas of 5 to 7 ft through Thu and to 9
ft Fri and Sat.


Latest scatterometer data continue to show light to gentle
variable winds N of the monsoon trough and gentle to moderate 
SW winds south of it. Seas across the region are in the 4-5 ft 
range in SW swell. Otherwise, scattered showers and isolated 
thunderstorms prevails in the offshore waters of Costa Rica, 
Nicaragua and Guatemala due to the passage of a tropical wave. 

For the forecast, a broad area of low pressure is expected to 
form in a few days a couple of hundred miles S of the coast of 
southern Mexico. Some slow development of this system is possible
thereafter as it moves WNW off the coast of Mexico.


Moderate to locally fresh NE winds continue over the waters 
N of the monsoon trough and W of 120W, with gentle to moderate 
winds S of the monsoon trough. Gentle to moderate N to NE winds 
and seas in the 5-7 ft range will change little into Tue. A NW 
swell expected to raise seas to 8 ft will move into the waters 
N of 27N between 120W-130W Tue into Wed, then subside. 

Looking ahead, another round of NW swell will accompany a cold 
front that will move into the waters N of 28N and W of 130W Tue 
night, with seas in excess of 8 ft dominating the waters NW of a
line from Guadalupe Island to 14N140W by late Thu.