Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 190920

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 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 0600 UTC surface analysis and satellite imagery through
0900 UTC.


Gulf of Tehuantepec Gale Warning: 
A recent scatterometer pass provided observations of minimal gale
force winds over the Gulf of Tehuantepec, with northerly winds of
20 to 30 kt extending downwind of the gulf to near 13N96W. Winds
are forecast to diminish below gale force this morning, and seas
will gradually subside during the day today. Winds of 20 to 30 kt
and seas of 8 to 10 ft are expected during the overnight and
early morning hours through early Saturday morning. 

In the Gulf of Tehuantepec, the first gale-force event of a
season typically occurs in mid-October. The 10-year climatology
indicates that on average 11.9 gale-force events and 6.3 storm-
force events occur in the Gulf of Tehuantepec each cold season.
About 84 percent of these events occur between November and
March, with the largest number of gale-force winds ocurring in
December. Storm-force events are most frequent in January. The
next gale-force wind event is forecast by the computer models to
occur in the Gulf of Tehuantepec Monday night into Tuesday as
another cold front moves across the Gulf of Mexico.


A tropical wave is N of 04N along 85W moving W at 10 to 15 kt.
Scattered moderate and isolated strong convection is noted within
about 150 nm E of the wave axis. This convective activity is
affecting parts of Honduras, Nicaragua and Costa Rica.


The monsoon trough axis extends from 10N85W to 08N100W to 10N120W.
The intertropical convergence zone axis continues from 10N120W 
to 11N130W to 09N140W. Scattered moderate convection is from 07N
to 09N between 91W and 105W. Isolated moderate convection is from
08N to 11N W of 110W. 



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 followed by a significant
swell event will reach the waters W of Baja California Norte, 
causing winds to increase to 20 to 25 kt, with building seas 
between 8 and 12 ft across the waters N of 26N. 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 prevaling
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 addtion, expect fresh to strong N 
to NW winds across most of the Gulf of California by early Sunday
morning, with seas building to 5 to 6 ft. These marine 
conditions are forecast to persist through Monday morning. 


Moderate to fresh offshore winds will develop across the Papagayo
region each night through tonight, 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 will reach the area between Ecuador 
and the Galapagos Islands this evening through Friday evening, 
building seas to 7 to 8 ft on Friday.


Scatterometer data indicate that 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,
aminly S of 06N W of 131W. 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 in the SW corner and far S central waters through 
Friday. The swell will then decay with seas subsiding to less 
than 8 ft during the upcoming weekend.

A cold front is forecast to reach the far NW corner of the 
discussion area this evening while weakening. A significant 
swell event will follow the front as it weakens and dissipates 
while moving across the forecast waters N of 28N. Seas will 
build to 10 to 17 ft over the NW waters tonight and Friday. This
swell event will continue to propagate SE covering the waters NW
of a line from 30N115W to 24N113W to 11N140W by Friday night 
with seas of 8 to 15 ft. By Saturday night, the highest seas of 
12 to 13 ft will dominate most of the waters N of 23N E of 125W, 
with seas of 8 to 12 ft affecting most of the area N of 05N 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 09:20:49 UTC