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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 280843

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Thu Sep 28 2023

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
0830 UTC.


A tropical wave is along 90W north of 05N to across portions of 
Central America, moving west at around 10 kt. Scattered moderate 
convection is noted from 05N to 07N between 87W and 89W.

A tropical wave is analyzed along 132W from 03N to 18N, moving W
at 10 to 15 kt. Scattered moderate isolated strong convection is
noted from 06N to 08N between 129W and 131W.


The monsoon trough extends from 09N83W to 09N95W to 07N105W. 
Segments of the ITCZ extend from 07N105W to 10N130W, and from 
09N133W to 11N140W. Scattered moderate convection is noted from 
05N to 07N between 123W and 125W.


Weak ridging extends across the region north of 22N, supporting 
moderate NW winds persist off Baja California, which is
accompanied by 8 to 12 ft seas in NW swell. Light to gentle 
breezes are observed elsewhere with 4 to 5 ft seas over open 
waters in southerly swell. Gentle southerly breezes and slight 
seas are evident in the Gulf of California. 

For the forecast, the long period NW swell in excess of 8 ft 
will persist off Baja California as far south as the 
Revillagigedo Islands into Fri, and will linger off Baja 
California Norte into Sat. Farther south, moderate to fresh N gap
winds will pulse to strong across the Gulf of Tehuantepec during
the early mornings though Sun. Looking ahead, fresh to strong 
westerly gap winds over the northern Gulf of California will 
start Fri evening, ahead of a weakening cold front, possibly 
reaching near-gale force by Sat evening. Expect moderate to fresh
winds off Baja California Sur early next week as high pressure 
builds in behind the front. 


Scattered showers and a few thunderstorms are noted within 90 nm
of the coast of Nicaragua and beyond 180 nm off Costa Rica and 
western Panama, south of the monsoon trough following the passage
of a tropical wave now extending through El Salvador. Light and 
variable breezes are evident off northern Central America, north 
of the monsoon trough, along with combined seas of 3-5 ft in 
southerly swell. Gentle to moderate southerly winds are noted 
south of the monsoon trough. Combined seas are 4-7 ft there, 
except 6-9 ft offshore Ecuador, highest south of the Galapagos 

For the forecast, gentle to moderate winds will prevail to the north
of 05N with seas 5 ft or less through Sun night, with moderate
SW winds farther south. Seas may build slightly in southerly
swell early next week. Seas south of 05N will be 6-9 ft in 
southerly swell through Fri evening, with seas highest to the SW 
of the Galapagos. 


Recent scatterometer satellite data from around 0530 UTC confirm
NE trade winds are starting to increase from 10N to 20N west of 
125W, where fresh to strong winds are evident. This is due to 
high pressure building north of 22N, and the passage of a 
vigorous tropical wave over the tropical waters west of 130W. 
Long- period NW swell has been propagating across most of the 
area north of 10N and west of 115W. The mix of the NW swell with 
the increasing trade winds has resulted in combined seas of 8 to 
12 ft from 10N to 20N and west of 125W as noted in altimeter
satellite data from around 0230 UTC. Farther south, cross- 
equatorial southerly swell of 8 to 10 ft is evident south of 07N 
and west of 105W, with moderate to fresh SE winds. Gentle breezes
and 5 to 7 ft seas are noted elsewhere. 

For the forecast, the tropical wave will continue westward, 
approaching 140W Fri morning. Some development of this system is 
possible over the next couple of days while it moves generally 
westward at about 10 to 15 kt. By late Fri, upper- level winds 
are forecast to become unfavorable for further development before
the system moves into the Central Pacific basin. At a minimum, 
fresh to strong seas and seas of 8-13 ft will accompany this 
feature. High pressure will dominate the waters elsewhere N of 
the monsoon trough/ITCZ. The pressure gradient will weaken by the
end of the week into the weekend as the tropical wave departs 
and the high weakens leading to improving conditions. Meanwhile, 
for seas, the northerly swell of 8 ft or greater will reach to 
the Equator and west of 115W by the end of the week, while the 
southerly swell of 8 ft or greater lingers near the Equator and 
southward. Both large areas of swell should gradually decay this 
by Sun.