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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 232150

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Thu Sep 23 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 1800 UTC surface analysis and satellite imagery through
2030 UTC.


The axis of a tropical wave is along 118W from 05N to 20N, 
moving west at 10 to 15 kt. Associated convection is occurring
near the monsoon trough and south of 14.5N, is described below. 

A 1009 mb low pressure center is near 19N124W and is accompanied
by active convection this afternoon. Scattered moderate isolated
strong convection is noted within 240 nm the NE and 210 nm SW 
semicircles. This system is forecast to move over cool waters 
and into an environment of stable air and strong upper- level 
winds, which should inhibit further development.

A tropical wave is analyzed along 137W from 10N to 18N, moving
westward at 10 to 15 kt. Associated active convection is confined
to along the ITCZ and is described below.


The monsoon trough extends from low pressure near 10N76.5W 1009 
mb to 08.5N86W to 11N96W to 13N121W. The ITCZ begins near 
11N126W to 09.5N135W to beyond 11N140W. Scattered moderate to 
strong convection is from 05N to 10N E of 87.5W, and within 30 
nm N and 180 nm of the ITCZ W of 127W. Scattered moderate convection
is from 07N to 14.5N between 90W and 118W.


Strong northerly gap winds to around 25 kt continue across the 
Gulf of Tehuantepec this afternoon and downstream to near 
12.5N97W. Peak seas have subsided to around 9 ft. These winds are
being forced by high pressure across eastern Mexico behind an 
early season cold front across the Gulf of Mexico. Elsewhere, a 
ridge continues to extend over the offshore forecast waters of 
Baja California providing mainly light to gentle NW to N winds as
shown by midday scatterometer data. Locally moderate NW winds 
are mainly along the coast and seas across the area remain 4 to 
6 ft. Light to gentle winds are also in the Gulf of California
and across the SW Mexico offshore waters, except for moderate
southerly winds in the far northern Gulf. Seas are in the 3 to 5
ft range for the SW Mexico offshore waters and up to 3 ft in the
Gulf of California. 

Northerly gap winds will continue across the Tehuantepec region
through Sunday, pulsing to strong each late night and early
morning. Surface ridging will continue to dominate the offshore
forecast waters of Baja California supporting mainly gentle to 
moderate NW to N winds through Mon. Light to gentle winds will 
dominate over the SW Mexico offshore waters. Otherwise, a surface
trough will move across the northern Gulf of California and will
support fresh to strong southerly winds through early this 
evening. After that, mainly light and variable winds are expected
across the entire Gulf through Mon. 


Gentle to moderate west to southwesterly winds will continue 
across the offshore waters of Costa Rica, Panama, Colombia and 
Ecuador today, then will diminish to light to gentle through Sat.
Winds will increase again to gentle to moderate Sat evening and 
continue through early next week. 

Light to gentle variable winds are forecast for the offshore
waters N of 10N with pulses of moderate NE to E winds in the 
Gulf of Papagayo over the weekend. Cross equatorial SW swell will
reach the forecast area early Sat, building seas to 6-7 ft 
across the regional waters through the weekend.


The northern forecast waters west of 120W remain under the 
influence of a surface ridge anchored by 1026 mb high pressure 
centered near 36N140W. The pressure gradient between the ridge 
and low pres center near 19N124W supports an area of moderate to
locally fresh NE winds roughly from 19N to 25N between 120W and
130W, and from 16N to 22N west of 130W. Seas are generally 7-9 ft
across this zone in mixed wind waves and NW swell. Winds across 
this area will gradually diminish over the weekend as the low 
shifts westward and weakens. Looking ahead, a cold front is 
expected to move into the NW waters early Tue and quickly weaken
as it moves southward. Associated NW swell is expected to raise 
seas to 8-10 ft.