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Eastern North Pacific Tropical Weather Discussion



419 
AXPZ20 KNHC 221606
TWDEP 

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Sun Jul 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 1200 UTC surface analysis and satellite imagery through
1530 UTC.

...TROPICAL WAVES...

A low latitude tropical wave is just along the coast of Colombia
along 77W from 01N to 11N, moving westward at 15 kt. The wave is
evident in tropical wave model diagnostics as well as a maximum 
in total precipitable water satellite imagery. Scattered moderate
isolated strong convection has quickly flared up along the wave 
to the south of the monsoon trough.

A tropical wave has its axis along 91W north of 04N to inland 
Guatemala and the Yucatan Peninsula, moving westward 10-15 kt. 
The wave is evident in 700 mb model guidance streamlines as well 
as a maximum in total precipitable water satellite imagery. 
Numerous moderate to strong convection is occurring from 10N-13N
between 90W-94W. Scattered moderate isolated strong convection is
seen where the wave intersects the monsoon trough within 180 nm 
west of the wave from 06N to 09N, and also within 30 nm of
11N94.5W. Little development is expected of this wave over the 
next couple of days.

A tropical wave has its axis extending from 06N120W to 14N121W to 
19N120W, moving westward 15 to 20 kt. The wave is associated 
with troughing at 700 mb as depicted in model guidance. 
Scattered moderate to strong convection is present where the wave
axis intersects the monsoon trough. This convection is located 
within 180 nm west of the axis from 08N-10N. Scattered moderate 
convection is within 30 nm of a line from 12N118W to 12N121W, 
and within 30 nm of 09N119W.

The previously tropical wave analyzed from 02N126W to 14N125W is
no longer identifiable in model guidance, and satellite imagery 
indicates no signature of this wave.

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

The monsoon trough axis extends from a 1010 mb low over NW
Colombia to 09N84W to 08N92W to weak low pressure of 1010 mb near
11N104W to 10N122W and to 11N130W, where latest scatterometer 
data indicates the ITCZ begins and continues to a 1008 mb low at
13N139W. Aside from convection associated with the tropical 
waves, scattered moderate isolated strong convection is within 
240 nm south of the trough between 77W-81W, within 180 nm south 
of the trough between 81W-87W and within 120 nm south of the 
trough between 123W-128W. Scattered moderate convection is within
180 nm south of the trough between 95W-100W. Similar convection 
is within 180 nm north and 120 nm south of the trough between 
105W-118W and south of the ITCZ from 07N-09N.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

The southeastward extent of rather weak high pressure ridging 
that enters the region well beyond 250 nm of the Mexican coast 
is analyzed near the Revillagigedo Islands near 16N106W. The 
ridge is maintaining light to moderate NW winds across the 
Mexican offshore waters, except for the Gulf of Tehuantepec area 
as discussed below. Little change is expected in these conditions
during the next several days. A long period SW cross-equatorial 
swell is affecting the waters S of 15N. This extensive swell 
event will continue spreading N and will cause seas to build to 
the range of 7-9 ft in the open waters for all the forecast zones
through Tue of the upcoming week.

In the Gulf of Tehuantepec, pulses of fresh to strong N gap 
winds will occur during the late night and morning hours until 
Mon morning. Wind waves generated by these N winds will interact 
with the SW swell event to produce mixed seas south of the Gulf 
peaking near 10 ft today before winds diminish early on Mon.
Seas near the Gulf of Tehuantepec will remain above 8 ft until 
early Tue, then subside slightly during Tue and into Wed.

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

Gulf of Papagayo: Fresh to strong easterly winds will pulse 
during the late night and morning hours through Tue morning, then
winds during this time frame will diminish to fresh. Seas from 
these NE to E winds will interact with the SW swell event to 
produce mixed seas in the Gulf as high as high as 10 ft on Mon 
before seas begin to slowly subside on Tue.

A low latitude tropical wave is just along the coast of Colombia.
See above for associated convective activity.

NE to E winds of only moderate speeds or weaker are forecast 
elsewhere N of the monsoon trough which will meander west of 
Central America between 07N and 10N. Moderate to fresh S to SW 
winds are generally expected S of the trough axis during the next
several days.

A long-period SW cross-equatorial swell event is already 
affecting the region as seas to the south of the equator have 
build to 9 ft. Seas will peak between 8 and 10 ft on Mon in the 
open waters, with the highest seas expected west of Ecuador.

REMAINDER OF THE AREA...   

A surface ridge extends southeastward from 32N140W to 24N122W 
and to near the Revillagigedo Islands near 16N106W. The gradient 
between the ridge and lower pressures found to its south is 
generally maintaining mainly moderate trade winds north of the 
monsoon trough south of 20N and west of 115W. Little change in 
this pattern is expected for the next several days. Swell to 8 
ft generated by strong winds N of the area is propagating S to 
cover the discussion waters N of 29N between 130W and 138W. This 
swell will continue to affect this region while slowly shifting 
westward through Mon.

A 1008 mb area of low pressure is centered near 13N139W, moving
westward around 15 kt. Fresh to strong winds are occurring 
within about 300 nm N of the low center with associated seas to 
10 ft. Scattered moderate convection is seen within 180 nm S and 
60 nm N of the low. Scattered moderate convection is present from
06N to 10N W of 135W. This low and its associated fresh to 
strong winds will move west of the discussion area by Mon 
morning. Residual producing seas of 8 ft in mixed E and S swell
from 14N to 18N W of 138W will subside to less than 8 ft by 
early Mon afternoon

Large long period SW swell is crossing the equator, with seas of
8 to 10 ft extending from the Southern Hemisphere northward to a
line from 03.4S83W to 00N86W to 12N103W to 14N123W to 04N137W, 
as confirmed by overnight satellite-derived sea height data. The 
swell will continue to propagate northward and allow for seas to 
build to 8 ft or above to most of the area S of 25N and east of 
133W Mon, before the swell decay and seas subside on Tue.

$$
Aguirre