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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 292208

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Thu Jul 29 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
2100 UTC.


Gale Warning: Showers and thunderstorms are becoming better
organized near a 1007 mb low pressure area centered along the 
monsoon trough near 12N108W. Environmental conditions are 
conducive for continued development, and a tropical depression is
expected to form during the next day or two while the system 
moves west- northwestward at 10 kt. Confidence is high enough 
that a gale warning has been issued preemptively. Numerous 
moderate to isolated strong convection is evident within 135 nm 
in the southeast semicircle of the low pressure. Fresh winds 
converging into the low pressure may be increasing to strong in 
some areas, and seas may be near 8 ft close to the center of the 
low pressure. 

Another 1007 mb low pressure area is centered farther west along
the monsoon trough near 13N124W. Upper level NW shear is keeping
scattered to numerous showers and thunderstorms within 90 to 210
nm to the east and southeast of the low. A recent altimeter
satellite pass indicated seas to 8 ft within 180 nm on the north
side of the low pressure, likely in fresh to strong winds. 
Environmental conditions remain conducive for continued 
development. There is a medium chance a tropical depression will 
form in the next couple of days, and a high chance of a tropical 
depression will form within the next five days while the system 
moves westward or west- northwestward at 10 kt.

Please see the latest NHC Tropical Weather Outlook at for more details on both these systems.


A tropical wave over the far eastern part of the area has been
reanalyzed to be a little farther east then previously thought,
and is now over the Caribbean and western Colombia near 77W. See
the Atlantic Tropical Weather Discussion at for
more information on this wave.

A tropical wave with its axis along 95W/96W extends from far 
southeastern Mexico and the Gulf Tehuantepec region to near 05N. 
It is moving westward at 10 to 15 kt. Scattered moderate convection
is evident from 10N to 13N between 93W and 98W. 

A tropical wave has its axis along 110W from 03N to 15N, moving 
west at 10 to 15 kt. No significant convection is evident with 
this wave.


The monsoon trough extends from the coast of Colombia near 07N78W
to across northern Panama to a 1007 mb low pressure near 12N108W
to 10N114W and northwest to another 1007 mb low pressure near 
13N124W and to 09N130W to beyond 10N140W. In addition to the 
convection described in the Tropical Waves section above,
scattered moderate convection is observed from 08N to 10N 
between 85W and 87W.


Fresh to strong north gap winds pulsing across the Gulf of 
Tehuantepec, between relatively higher pressure to the north of 
the region and lower pressure farther south, are starting to
diminish. Light to gentle variable winds are elsewhere with seas
mainly to 3 to 5 ft due to a south to southwest swell.

Farther north, a relatively weak pressure gradient supports 
gentle to locally moderate northwest winds over the Baja 
California offshore waters with seas in the 3 to 5 ft range in SW

For the forecast, the pattern will continue to support gap winds
across the Gulf of Tehuantepec and off western Oaxaca tonight 
through Sun, mainly at night and in the early morning hours. 
Winds will increase slightly and seas will build near Clarion 
Island Sat as the gale center near 12N108W moves westward, 
possibly as a tropical depression or storm, well to the south of 
the island. Mostly moderate winds and seas will persist 
elsewhere. Looking ahead, seas will build off southern Mexico 
starting late Sat due to increased southerly swell. 


Gentle to moderate south to southwest winds will remain 
south of the monsoon trough through the forecast period along 
with a southwest swell that will build seas to 5-7 ft. Seas of 
3-6 ft due to a southwest swell will change little over Gulf of 
Papagayo region during the next few days.

For the forecast, Fresh to strong gap winds will pulse mainly at night
and in the early morning tonight into Sun. Elsewhere, gentle to 
moderate south to southwest winds will dominate the waters south 
of the monsoon trough through the forecast period along with 
southwest swell. 


See the Special Features section above for details on two low 
pressure systems that have potential for tropical cyclone 

Aside from the two Special Features low pressure systems, 
relatively weak high pressure is present with the associated 
gradient allowing for generally moderate northeast trades to 
persist north of the monsoon trough and moderate south to 
southwest winds farther south, with 5 to 7 ft seas in mixed swell
in most areas. Larger southerly swell is noted south of the 
equator. Winds and seas over some sections of the area will be 
impacted by the Special Features low pressure systems during the 
next several days.