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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 171557

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1556 UTC Tue Jul 17 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. 


A tropical wave is analyzed N of 05N along 90W and is estimated 
to be progressing W at 12 kt. No significant convection is
observed with this wave.

A tropical wave is analyzed from 04N to 14N near 109W. Scattered
moderate convection is noted where the tropical wave intersects
the ITCZ from 07N to 09N between 108W and 110W. 

A tropical wave is analyzed from 08N123W through a 1009 mb 
surface low embedded along the wave at 14N122W to 17N121W. This 
system is moving W at 10 to 15 kt. Scattered moderate and 
isolated strong convection is observed from 14N to 17N between
119W to 121W. Earlier scatterometer passes showed fresh easterly
flow within 180 nm either side of the wave axis from 13N to 15N.
A concurrent altimeter satellite pass showed seas to 8 ft.


The monsoon trough extends from 09N78W to 08N100W. The ITCZ
continues from 08N100W to the tropical wave near 109W, then on to
10N116W. The ITCZ continues from the 1009 mb low pressure near
14N122W to 09N130W to 10N140W. Scattered moderate convection is
noted within 120 nm either side of the ITCZ west of 125W.



A scatterometer pass from the previous evening along with reports
from Salina Cruz on the coast of Mexico near the Gulf of 
Tehuantepec indicated fresh to strong drainage flow into the 
Gulf of Tehuantepec earlier this morning. This flow is being
enhanced between high pressure over the western Gulf of Mexico 
and a tropical wave passing westward south of the region, and 
strong nocturnal winds with seas to 7 ft are expected into Thu 
morning. Light to gentle breezes and minimal seas are noted 
elsewhere over Mexican offshore waters. 

Divergent flow aloft associated with a mid to upper low over
northwest Mexico is supporting scattered overnight showers and 
thunderstorms inland over the mountainous terrain east of the 
Gulf of California. Some of this activity is currently impacting
the southern Gulf of California. This may repeat again tonight,
but taper off early as the mid/upper low migrates through the

Looking ahead, long period southwest swell will propagate into
the Mexican offshore waters by Fri, with combined seas in open 
waters building in excess of 5 ft. 


Gulf of Papagayo: Strong nocturnal drainage flow, accompanied by 
6 to 8 ft seas, are expected through Thu night with extended 
guidance suggesting these conditions will resume on Sun night. 

Gentle to occasionally moderate E winds are forecast elsewhere N 
of the monsoon trough which is meandering between 07N and 10N. 
Moderate southerly winds are forecast S of the monsoon trough 
for the next several days accompanied by 4 to 6 ft seas.

Long period southerly swell, in the form of 7 to 8 ft seas, will 
pass north of the Equator by Thu, and propagate northward into
the offshore waters of Central America through Sat.


A broad upper low is centered near 21N127W, supporting an
associated 1009 mb surface low near 14N122W along a tropical 
wave. While upper winds are unfavorable for further development, 
scatterometer data confirms fresh to occasionally strong easterly
flow in a swath on the northern side of the surface low through,
with seas observed at 8 ft. The tropical wave will continue 
west, reaching 130W by Thu, with the low gradually dampening out 
as the upper lift north of the area, allowing winds and seas to 
diminish. The subtropical ridge will build north of 20N, 
supporting moderate to fresh trade winds from 08N to 15N west of 
130W by late week.

Long period cross-equatorial swell, in the form of 7-9 ft seas, 
will move across the Equator between 90W and 125W on Wed, and 
continue to propagate N across the discussion area through Sat.