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Eastern North Pacific Tropical Weather Discussion



222 
AXPZ20 KNHC 210347
TWDEP 

Tropical Weather Discussion 
NWS National Hurricane Center Miami FL
0405 UTC Fri Sep 21 2018 

Tropical Weather Discussion for the eastern Pacific Ocean from 
the Equator to 32N, east of 140W. The following information is 
based on satellite imagery, weather observations, radar, and 
meteorological analysis.

Based on 0000 UTC surface analysis and satellite imagery through 
0345 UTC.   

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... 

The monsoon trough extends W off the Caribbean coast of Colombia  
at 08N77W, and continues west across the northern Gulf of Panama 
and central Panama to the Pacific Coast of Costa Rica at 09N84W 
to 11N105W to 10.5N117W where it loses identity in the cyclonic 
circulation associated with a 1010 mb surface low at 14.5N124W.
The monsoon trough resumes southwest of the low at 13N125W and 
continues southwest to 10N133W. Scattered moderate isolated 
strong convection is observed within 180 nm either side of a 
line from 07N83W to 13N94W, and within the area bounded by 
06N to 15N between 102W and 119W.  

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO... 

Gulf of California: Gentle to moderate variable winds forecast 
across the gulf waters north of 30N through the upcoming weekend.
Otherwise, light to gentle variable winds expected through the
middle of next week.

Gulf of Tehuantepec: Fresh to locally strong nocturnal flow 
forecast through Tue with strong drainage flow forecast for Tue 
night through Thu night with seas building to 8 ft.

A ridge will meander from 22N116W to 14N97W through early next 
week. Gentle NW flow is forecast W of the Baja California 
through Sat except becoming a moderate NW breeze within 90 nm of 
the coast during the late afternoons and evenings. A tightening 
pressure gradient on Sat night will support moderate northwest 
flow west of Baja, except increasing to a fresh breeze during 
the evenings within 90 nm of the coast through Tue. 

Extended model guidance suggests a surface low will develop near 
12N103W on Sun night, and track northwest across the offshore 
waters seaward of 200 nm reaching near 17N109W on Wed.   

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND 
WITHIN 750 NM OF ECUADOR...

Gulf of Papagayo: Moderate to locally fresh east nocturnal 
drainage flow expected through Mon night. 

Light and variable winds are forecast elsewhere N of the monsoon 
trough which is meandering between 09N and 11N. Moderate 
southwest flow is forecast S of the monsoon trough through the 
middle of next week when long period SW swell, in the form of 6 
to 8 ft seas, will propagate northeast reaching the far offshore 
waters near 09N90W during the middle of the next week.  

Looking ahead, an increase in moist southwest flow is suggested 
by the major global models by early next week, possibly 
culminating in a Central American gyre pattern by the middle of 
next week.  This may bring increase showers and thunderstorms to 
the Pacific waters off Central America.

REMAINDER OF THE AREA...   

A 1010 mb surface low is analyzed near 14.5N124W and is 
accompanied by scattered moderate isolated strong convection 
extending southwest along a segment of the monsoon trough within 
75 nm either side of a line from 15.5N122.5W to 08N138W.
The low pressure area will weaken into a trough by Sun, and move 
west of the area early next week.

A broad ridge continues across the subtropics with an area of 
fresh north winds and 7 to 9 ft seas forecast across the waters 
north of 28N between 123W and 129W through early Fri. Fresh 
northeast trades and diminishing across the waters from 13N to 
19N west of 138W.

$$
Nelson