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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 201606

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Mon Sep 20 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 1200 UTC surface analysis and satellite imagery through
1500 UTC.


The axis of a tropical wave is along 101W and N of 06N, moving 
west at 10 to 15 kt. Scattered moderate convection is noted from 
07N to 13N between 100W and 106W.

The axis of a tropical wave is along 111W from 07N to 20N, moving
west at 10 to 15 kt. Scattered moderate convection is seen from 
14N to 20N between 106W and 114W.

The axis of a tropical wave is along 123W from 07N to 17N, moving
west at around 10 kt. Convection is limited near the wave axis. 


The monsoon trough extends from 09N84W to 11N100W a 1011 mb low 
pressure near 11.5N116W to 09N130W. The ITCZ continues from 
09N130W to 06N140W. Aside from the convection associated with the
tropical waves, scattered moderate convection is from 05N to 09N
E of 85W to the coast of Colombia. A cluster of moderate convection
is over the Gulf of Tehuantepec. Scattered moderate to isolated 
strong convection is noted from 08N to 12N between 112W and 120W.
The latter convective activity is mainly associated with the 
above mentioned low pressure.


A ridge dominates the offshore forecast waters of Baja California
producing mainly gentle to moderate NW-N winds. Seas are in the
4-6 ft. Light to gentle winds are seen elsewhere offshore of SW 
Mexico with seas in the 3 to 5 ft range. Light SE-S winds prevail
in the Gulf of California. Some shower activity is observed in 
parts of the central and southern Gulf of California and also 
near Los Cabos area.

For the forecast, a ridge will continue to dominate the offshore
waters of Baja California. Seas will build to 8 ft in NW swell N
of Punta Eugenia tonight. A gap wind event is expected in the 
Gulf of Tehuantepec beginning late Tue night with gale conditions
possible Wed to Thu night. Seas are forecast to build to 9 or 10
ft with this event.


Gentle to moderate southerly winds will prevail across the
offshore waters of Costa Rica, Panama, Colombia and Ecuador
during the forecast period with seas of 4-6 ft in SW swell.
Mainly light and variable winds are forecast across the offshore
waters from Guatemala to northern Costa Rica with seas of 3-5 ft
also in SW swell. In the Papagayo region expect moderate NE-E 
winds through Tue. 


A weakening frontal boundary is located just N of area and
extends from near the California/Baja California border to
30.5N128W. An altimeter pass indicates seas to 10 ft in the wake
of the front. These seas will propagate across the northern
forecast waters in NW swell trough late Tue or Tue evening.

The northern forecast waters are under the influence of a ridge 
anchored by a 1028 mb high pressure located near 40N135W. 
Moderate to locally fresh trades are noted along the southern 
periphery of the ridge with seas of 5-7 ft based on altimeter 

An area of low pressure is forecast to form several hundred miles 
southwest of the southern tip of the Baja California peninsula 
within the next couple of days. Thereafter, some gradual development
of this system is possible, and a tropical depression could form
by the latter part of this week while it moves west-northwestward
to northwestward at 10 to 15 mph. Regardless of development, 
winds may increase to fresh to strong with seas to around 9 ft on
the E side of the low center. At 1200 UTC, a 1011 mb low
pressure is analyzed along the monsoon trough near 11.5N116W.