Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 191602

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1501 UTC Thu Oct 19 2017

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
1430 UTC.


Gulf of Tehuantepec Gale Warning: 
High pressure along the Sierra Madre Oriental of Mexico is 
weakening, which is allowing the pressure gradient over the 
isthmus of Tehuantepec to relax. Winds are still expected to 
diminish below gale force over the Gulf of Tehuantepec by mid 
afternoon today. Seas in this area will gradually subside as 
well. Winds of 20 to 30 kt and seas of 8 to 10 ft are then 
expected during the overnight and early morning hours through 
early Saturday morning. Strong gap winds from Sat through Sun 
will occur during the nocturnal drainage maximum and be 
restricted to N of 15N until late Sun night, when winds over the 
Gulf of Tehuantepec will ramp up again in response to the next 
cold front entering the Gulf of Mexico.


A tropical wave is N of 03N along 86W moving slowly W around 5 
kt. Scattered moderate and isolated strong convection is noted 
from 05N to 10N between 82W and 88W. This convection is situated 
just SW of the coasts of Panama and Costa Rica.


The monsoon trough axis extends from 09N84W to 08N103W to 
09N110W to 10N120W. The intertropical convergence zone axis 
continues from 10N120W to 11N127W to beyond 09N140W. Scattered 
moderate and isolated strong convection is present within 60 nm 
either side of a line from 10.5N123W to 12.5N129W to 12.5N133W. 
Scattered moderate convection is seen from 06N to 10N between 94W
and 107W and from 07N to 10N between 122W and 124W.



Please see the Special Features section above for information 
about the ongoing Gulf of Tehuantepec gale event.

A weakening surface ridge extends SE into the waters off Baja 
California, producing mainly gentle to moderate NW to N winds and
seas of 5 to 7 ft along the Pacific coast of Baja. A weakening 
cold front will reach 30N140W late tonight. By Friday evening, 
the front will have lost identity near Baja but will usher in a 
significant swell event from Fri evening through Mon. High 
pressure building in behind the front will cause winds to 
increase to 20 to 25 kt, with building seas between 8 and 12 ft 
across the waters N of 26N during the day on Fri. Seas will 
continue to build to 14 to 16 ft in NW swell N of 27N Friday 
night. This swell event will continue propagating SE across the 
remaining offshore forecast waters W of Baja California, reaching
the Revillagigedo Islands Saturday evening. High pressure in the
wake of the front will dominate the northern forecast waters 
during the upcoming weekend. As a result, fresh to strong NW 
winds will persist over the offshore waters west off Baja 
California through early Saturday, with moderate to fresh NW 
winds prevailing thereafter. The pressure gradient between the 
high pressure and lower pressure in the vicinity of the Monsoon 
Trough/ITCZ will also bring mainly fresh trade winds across the 
west-central waters during the weekend. In addition, expect fresh
to strong N to NW winds to commence across the Gulf of 
California by dawn on Sunday, the spread SE over the remainder of
the Gulf Sun night and Mon with seas peaking at 5 to 6 ft. Winds
will subside below advisory levels by Mon evening, but 
reinforcing NW swell will maintain seas above 8 ft W of Baja 
through the middle of next week.


Moderate to fresh offshore winds will develop nightly across the
Papagayo region through Sat night, accompanied by seas of 5 to 7
ft. Otherwise, light and variable winds and seas of 4 to 6 ft in
SW swell will prevail N of the monsoon trough, while gentle to 
moderate SW to W winds and seas of 5 to 7 ft in SW swell will 
prevail S of the trough.

Long period S to SW swell reaching the area between Ecuador and 
the Galapagos Islands will maintain seas around 8 ft this evening
through Friday evening. Moderate to fresh SW winds will cause 
seas to build to around 8 ft W of Colombia and S of Panama 
between 03N and 06N between 80W and 84W.


Gentle to moderate winds dominate the northern forecast waters 
under the influence of a ridge being weakened by an approaching 
cold front. Seas continue to subside across most of the region W 
of 110W. An area of 8 ft seas primarily in SE swell is present 
across the SW corner, mainly S of 04N and W of 135W. A new set of
long period S to SW swell is forecast to cross the Equator today
and propagate across the far southern waters, with resultant 
combined seas building back to 8 ft near the SW corner of the 
discussion area and in the waters near the Equator to the W of 
the Galapagos Islands through Friday night. The swell will then 
decay with seas subsiding to less than 8 ft this weekend.

A cold front will reach the far NW corner of the discussion area
this evening as it weakens. However, the large fetch of gales 
that has been in place to the NW of the front has already 
generated large long period swell which are propagating SE. 
Consequently, a significant swell event is expected. Seas will 
build to 10 to 16 ft over the NW waters tonight and Friday. The 
swells will continue to propagate SE to bring 8 ft seas to the 
waters NW of a line from 27N115W to 14N140W by Friday night. Seas
will be highest at around 15 ft near 30N 130W. By Saturday 
night, the highest seas of 12 to 13 ft will dominate most of the 
waters N of 23N E of 125W. Seas of 8 to 12 ft will affect most of
the area N of 08N W of 110W. Seas of 8 ft or greater will reach 
all the way to 110W on Sunday then continue to propagate SE, but 
begin to gradually decay thereafter through early next week.


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Page last modified: Thursday, 19-Oct-2017 16:02:59 UTC