277 
AXPZ20 KNHC 222128
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2127 UTC Sat Sep 22 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 1800 UTC surface analysis and satellite imagery through
2100 UTC.
    
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... 

A segment of the monsoon trough extends from 10N85W to 11.5N107W
to 09N123W. Another segment of the monsoon trough reaches from 
11.5N130W to 11.5N140W. Scattered moderate convection is ongoing
beyond 120 nm off the coast of Mexico from 11N to 15N between 
95W and 102W. 
     
...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO... 

Strong gap winds will pulse into the Gulf of Tehuantepec over the
next several nights both ahead of and in the wake of the northern
extent of a tropical wave that will move across southern Mexico
through early next week. A sharp upper trough over the Gulf of
Mexico is enhancing leftover convection off southern Mexico and
north of the monsoon trough. Major global models are indicating
development of broad low pressure south of the Revillagigedo
Islands Sunday through Tue moving westward, although they still 
differ on exact location. 

A surface trough is analyzed from 15N106W to just off the coast
of Cabo Corrientes. A few showers and thunderstorms are active
within 60 nm west of trough from 15N to 18N. The trough and
accompanying weather may drift west to Socorro Island by late Sun
before dissipating. 

Farther north, weak ridging will persist across the region north
of 20N, maintaining generally moderate NW flow off the coast of 
Baja California, becoming locally 15 to 20 kt near the coast 
north of Cabo San Lazaro during the late afternoons. Light to 
gentle breezes along the Gulf of California will become more 
southerly by late Sun as high pressure builds over northwest 
Mexico. 

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. Moderate to fresh southwest monsoonal flow 
is expected south of 10N late next week as a surface low begins
to develop near 12N92W on Thu, and then tracks northwest of the
area on Fri accompanied by thunderstorms. 

REMAINDER OF THE AREA...   

A surface trough is analyzed along 130W from 11N to 19N. An
earlier altimeter satellite pass indicated seas to 8 ft along 
this trough axis, which could also indicate there are fresh to 
strong winds on the northern end of the trough, facing ridging to
the north. Scattered showers and thunderstorms in this area 
appear to be weakening through the early morning. 

A broad ridge continues across the subtropics accompanied by 
moderate to locally fresh anticyclonic flow south of 23N west of 
120W, with strongest winds near the trough. The trough will move
west of 140W by early Tue, with ridging building into the deep
tropics in its wake, allowing a large areal extent of fresh trade
winds. Looking ahead, global models indicate the potential for 
low pressure to develop along the monsoon trough around 10N130W 
by Wed, but differ on whether this will deepen much as it move
westward through late week. Similarly, a more developed low
pressure area farther east will move westward and to the south 
of the Revillagigedo Islands through mid week.

$$
Christensen