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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 271941

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Wed Sep 27 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 1800 UTC surface analysis and satellite imagery through
2000 UTC.


A tropical wave is along 87W north of 05N to across portions of
Central America, moving west at around 10 kt. Scattered moderate
isolated strong convection is noted from 03N to 12N between 82W
and 94W.

A tropical wave is analyzed along 129W from 03N to 18N, moving W
at 10 to 15 kt. Scattered moderate isolated strong convection is
noted from 11N to 16N between 124W and 131W.


The monsoon trough extends from 09N80W to 10N98W to 09N106W to
10N118W. Segments of the ITCZ extend from 10N118W to 10N127W, 
and from 09N132W to 09N139W. Scattered moderate isolated strong 
convection is noted from 04N to 11N between 119W and 140W.


A ridge extends across the offshore waters W of Baja California 
with a trough extending along the Gulf of California. Moderate 
NW-N winds are offshore Baja California from near Cabo San Lazaro
northward per recent ASCAT scatterometer data, with seas of 7-11
ft in NW swell. A plume of moderate to fresh N-NE winds is in 
the Gulf of Tehuantepec. Winds are mainly light to gentle 
elsewhere, along with 4-6 ft seas in typical mixed S and NW 
swell. In the Gulf of California, seas are 1-3 ft, except 3-4 ft 
near the entrance.

For the forecast, seas of 7-11 ft in NW swell will persist 
through Thu offshore Baja California before slowly subsiding Fri 
through Sat. Farther south, moderate to fresh N gap winds will 
pulse to strong across the Gulf of Tehuantepec at night. 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. Winds
may increase to moderate to fresh offshore Baja California Sur
early next week as high pressure builds in behind the front.


A tropical wave is moving just W of the Papagayo region as 
described above. Light and variable breezes are evident off 
northern Central America, N of the monsoon trough, along with 
combined seas of 3-5 ft in southerly swell. Gentle to moderate 
southerly winds are noted S of the monsoon trough per recent 
ASCAT scatterometer data. Combined seas are 4-7 ft there, except 
5-8 ft offshore Ecuador, highest S of the Galapagos Islands.

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 build to 6-9 ft in 
southerly swell through Fri evening, with seas highest to the SW 
of the Galapagos. 


A tropical wave described above along 129W combined with high 
pressure N of the monsoon trough/ITCZ is supporting a growing 
area of fresh to strong winds roughly from 12N to 23N between 
124W and 140W as confirmed by recent ASCAT scatterometer data. 
Moderate to fresh trades cover the remainder of the waters N of 
the monsoon trough/ITCZ and W of 117W. A large area of northerly
swell of 7-11 ft roughly N of 13N and W of 114W, up to around 12
ft N of 25N between 119W and 130W per earlier altimeter data. To
the south, mainly moderate southerly winds are S of the monsoon 
trough/ITCZ. Southerly swell of 7-10 are S of 05N and W of 110W. 
Mainly gentle winds and 4-7 ft seas cover the remainder of the 
open waters.

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 this weekend, 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 W 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 weekend.