Tropical Weather Discussion
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AXPZ20 KNHC 181603

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1512 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 1200 UTC surface analysis and satellite imagery through
1430 UTC.


Gulf of Tehuantepec Gale Warning:
Gale force winds continue over the Gulf of Tehuantepec. Recent
satellite-derived wind data indicated 11 ft seas in the vicinity
of the Gulf of Tehuantepec, suggesting the current gale event is
still in progress. This gap wind event continues as result of a
tight pressure gradient between high pressure over the eastern
slopes of the Sierra Madre Mountains in Mexico. Seas remain in
the range of 10 to 15 ft within the area of gale force winds.
with seas of 8 ft or greater are propagating downwind from 09N to
13N between 93W and 100W. Global model guidance remains
consistent in indicating that the current event has peaked and
that high pressure adjacent to the eastern Gulf will weaken
through Friday, allowing the pressure gradient over the Isthmus
of Tehuantepec to slacken. Winds are still expected to fall below
gale force just after sunrise on Thursday. However, northerly
winds of 20 to 30 kt and seas of 8 to 10 ft will persist through
Friday. Winds over the Gulf of Tehuantepec will pulse to strong
speeds during the overnight hours on Sat night and Sun, before
another gale force wind event commences Mon night.


A tropical wave is N of 06N along 85W, moving W at 10 to 15 kt.
Virtually all of the convection associated with this wave remains
north of the Pacific coasts of Panama and Costa Rica and inland
over Nicaragua.


The monsoon trough axis extends W from Panama and Costa Rica
to 09N84W to 08N100W to 10N114W to 10N118W. The intertropical
convergence zone axis continues from 10N118W to 07N133W to
beyond 08N140W. Scattered moderate and isolated strong
convection is noted from 07N to 11N between 93W and 95W, from
07N to 10N between 105W and 112W and from 06N to 12N between
117W and 128W.



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

A 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. 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 evening a weakening cold front and accompanying set of
large NW swell will propagate into the waters W of Baja
California, causing seas to build to between 8 and 12 ft across
the waters N of 26N. Seas will continue to build to 14-16 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 on Saturday. Also on Friday, expect increasing winds of 20
to 25 kt over the waters adjacent to Baja California Norte as
high pressure building in the wake of the front tightens the
pressure gradient over the northern forecast waters. These winds
will subside on Sat.

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 stay mainly 2
ft or less, except for higher seas of 3 to 5 ft at the entrance
to the gulf in SW swell. Seas will subside to 3 to 4 ft Wednesday
through Thursday night, and then to 2 to 3 ft on Friday. Seas
will rebuild 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 Saturday night, accompanied by 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.

Long period S to SW swell will reach the area between Ecuador
and the Galapagos Islands Thursday evening through Friday evening,
building seas to 7 to 8 ft on Friday.


Elsewhere, gentle to moderate winds are noted across 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 S of 05N W of 130W. A new set of
long period S to SW 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 the swell
decay and seas subside below 8 ft during the upcoming weekend.

Looking ahead, models agree in bringing a cold front to the far
NW corner of the discussion area Wednesday evening. A
significant swell event will follow the front as it weakens and
dissipates. Seas will building to 10 to 17 ft over the NW waters
Thursday night and Friday. The seas will spreading across all of
the waters N of 08N and W of 110W by Fri evening, then across all
of the waters N of the Equator and W of 108W by Sunday night.
Seas of 8 ft or greater will reach all the way to 110W by early
Sunday then continue to propagate SE but begin to gradually
decay thereafter.

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