AXPZ20 KNHC 282054

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Tue Sep 28 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 2045 UTC.


A tropical wave has its axis along 110W from 03N to 17N moving west at 10-15 kt. A very moist atmospheric environment surrounds this wave. Scattered moderate convection is within 120 nm either side of the wave from 12N to 15N.


The monsoon trough extends from 1010 mb low pressure over northern Colombia near 09N76W to 10N85W to low pressure near 09N88W 1010 mb to 13N100W to low pressure near 14N106W 1011 mb to 13N116W to low pressure near 12N123W 1010 mb and to 12N132W. An ITCZ segment extends from 10N133W to beyond 09N140W. Numerous moderate to isolated strong convection is seen from 03N to 09N between 77W-84W, from 05N to 09N between 84W-88W and within 180 nm in the NE quadrant of the 1011 low near 14N106W. Scattered moderate convection is within 120 nm north of trough between 116W-121W, also between 123W-125W, within 90 nm either side of trough between 98W-100W and within 60 nm south of the trough between 122W-125W.


Moderate to fresh northwest-north winds are present west of Baja California, the strongest offshore of Baja California Sur. Mainly light to gentle winds prevail elsewhere offshore of Mexico, except locally moderate to fresh in the central and northern Gulf of California. Seas are in the 5-7 ft range in mixed long-period northwest and south swell, except 3-5 ft due to a south to southwest swell from Cabo Corrientes to the entrance to the Gulf of California, and 1-3 ft in the central and northern Gulf of California, locally to 4 ft.

For the forecast, moderate to fresh winds offshore of Baja California and in the northern Gulf of California will diminish to gentle speeds on Thu. A broad area of low pressure located a few hundred nautical miles south of Manzanillo, Mexico may bring increasing winds and seas to the vicinity of the Revillagigedo Islands and southern Baja California by the end of the week into the weekend as low pressure may develop along it and move west- northwestward. Otherwise, mainly gentle winds will prevail offshore of Mexico through the week and into the weekend. Large NW swell will impact the waters west of Baja California by tonight, subsiding by the end of the week.


Moderate to fresh northeast to east winds are noted in the Papagayo region. Light to gentle winds are noted elsewhere north of the monsoon trough, higher in and near thunderstorms including in the vicinity of the Gulf of Panama. Moderate S-SW winds prevail south of the monsoon trough. Seas are mainly in the 5-7 ft range in mixed long-period southwest and northwest swell.

For the forecast, the moderate to fresh offshore winds in the Papagayo region will become gentle east to southeast winds Thu. Otherwise, light to gentle winds will prevail north of he monsoon trough, with mainly moderate south-southwest winds south of the monsoon trough. Cross-equatorial southwest swell will propagate through the regional waters during the next several days.


The remnants of a former cold front are analyzed as a trough from 27N117W to 26N123W and to 28N128W. Stronger high pressure is beginning to build southward across the northern section of the area, with the resulting gradient bringing mainly fresh north to northeast winds over those waters. With this surge of winds, a large set of northwest to north swell producing seas of 8-10 ft has infiltrated the waters northwest of a line from 30N120W to 27N129W and to 23N140W. Weaker high pressure is analyzed elsewhere over the area. The resultant lighter gradient is allowing for generally moderate to fresh northeast to east trades to exist from just north of the monsoon trough area to near 26N. The majority of the fresh trades are confined to west of about 130W. Seas there are in the 5-7 ft range in mixed south and northwest swell.

For the forecast, the trough will continue to move and dissipate by early Wed afternoon. The northwest to north swell will continue to propagate through the northern and central waters through late Thu while gradually decaying. No other large swell set is forecast to impact the discussion area during the next several days.

$$ Aguirre