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
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.
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
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.
...OFFSHORE WATERS WITHIN 250 NM OF MEXICO...
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.
...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA,
COLOMBIA, AND WITHIN 750 NM OF ECUADOR...
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.
...REMAINDER OF THE AREA...
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