Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 180930

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
601 UTC Wed Oct 18 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 0600 UTC surface analysis and satellite imagery through
0900 UTC.


Gulf of Tehuantepec Gale Warning: 
Gale force winds are blowing across the Tehuantepec area. Salinas
Cruz, Mexico is reporting sustained N winds of 25 kt. This gap
wind event is the result of a tight pressure gradient between
high pressure across the eastern slopes of the Sierra Madre
Mountains in Mexico, and across the western Gulf of Mexico in the
wake of a stationary front which extends from N to S over the
central Bay of Campeche. Seas are in the range of 10 to 15 ft
across the area of gale force winds, with seas of 8 ft or 
greater spilling out to areas downwind of the gale. Global model 
guidance indicates that the high pressure will weaken through 
Thursday, with the corresponding tight gradient slackening. This 
will allow for the gale force winds to eventually diminish to 
below gale force just after sunrise on Thursday, however, 
northerly winds of 20 to 30 kt will continue through Friday along
with seas of 8 to 10 ft. Looking ahead, another gale force wind 
event is possible early next week.


A tropical wave is N of 06N along 83W, moving W at 10 to 15 kt. 
A cluster of moderate to isolated strong convection is along the
wave axis near 13N. This convective activity is currently 
affecting Nicaragua. 


The monsoon trough axis extends across parts of Panama and Costa
Rica near 10N86W to 08N100W to 09N110W. The intertropical 
convergence zone axis continues from 09N110W to 10N120W to 07N135W
to beyond 09N140W. Scattered moderate to strong convection is 
noted along the coast of Colombia N of 03N, and in the Gulf of 
Panama N of 07N. Scattered moderate isolated strong convection 
is from 08N to 11N between 94W and 100W, and from 08N to 11N 
between 110W and 130W.



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

A surface ridge extends across the waters off Baja California, 
producing mainly gentle to moderate NW to N winds and seas of 5
to 7 ft. The ridge will remain in place during the next few days
with little change in winds and seas over the offshore waters 
aside from the Gulf of Tehuantepec region as described above. By 
Friday afternoon into Friday evening a weakening cold front and 
accompanying set of large NW swell will propagate through the 
waters W of Baja California building seas to 8 to 12 ft across
the waters N of 27N. Seas will continue to build to 14-15 ft in
NW swell by Friday night. This swell event will continue to
propagate across the offshore forecast waters on Saturday. Also 
on Friday, expect increasing winds of 20to 25 kt over the waters
adjacent to Baja California Norte as high pressure in the wake 
of the front begins to dominate the northern forecast waters.

Mainly gentle to moderate NW to N winds are expected over most 
of the Gulf of California through early Wednesday, then winds 
become light and variable through Friday. Seas will be mainly 2 
ft or less, except for higher seas of 3 to 5 ft at the entrance 
to the gulf in SW swell subsiding to 3 to 4 ft Wednesday through
Thursday night, and then to 2 to 3 ft on Friday. Seas will build
back to 3 to 5 ft near the entrance during the upcoming weekend
as southerly swell reaches the area.


Moderate to fresh offshore winds will develop across the Papagayo
region each night through Thursday night, with seas of 5 to 7 
ft. 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.

Swells originating from the gale force wind event in the Gulf of
Tehuantepec will reach the far western section of the offshore 
waters of Guatemala and El Salvador, building seas to 8 to 10 ft
there through this afternoon, subsiding to 6 to 8 ft this 
evening, and to 5 to 6 ft on Thursday. Long period SW swell is 
forecast to reach the area between Ecuador and the Galapagos 
Islands from Thursday evening into Friday, building seas to 7 to
8 ft on Friday.


The low pressure area previously located near 24N128W has 
weakened, and a surface trough is analyzed on the 0600 UTC 
surface map extending from 22N128W to 27N128.5W. Winds and seas 
have diminished in association with this feature. 

The low pressure area located over the west-central waters near 
16N140W has also weakened and now a trough is analyzed west of
the forecast region. Seas of 8 to 9 ft in mixed NE and NW swell
are still noted over the forecast waters in association with 
this trough from 15N to 21N W of 136W. A pair of altimeter 
passes confirmed the presence of these sea heights.

Elsewhere, gentle to moderate winds are noted across the 
northern forecast waters under the influence of a weak ridge. 
Seas continue to subside across most of the region W of 110W 
with an area of 8 ft seas in mixed swell S of 05N W of 130W. A 
new set of long period southerly swell is forecast to cross the 
Equator on Thursday and propagate across the far southern waters 
with resultant combined seas building back to 8 to 9 ft in the SW
corner and far S central waters through Friday before decaying 
during the upcoming weekend.

Looking ahead, a cold front is forecast by the global models to 
reach the far NW corner of the forecast region by Thursday night.
A significant swell event will follow the front, with seas 
building to 10 to 17 ft over the NW waters Thursday night into
early Friday before spreading across all the northern waters W 
of 115W, and across the west-central waters by late Friday night.
Seas of 8 ft or greater will reach all the way to 110W by early
Sunday then will begin to gradually decay while reaching to 100W


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Page last modified: Wednesday, 18-Oct-2017 09:30:33 UTC