Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 180221

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0221 UTC Tue Oct 17 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 0000 UTC surface analysis and satellite imagery through
0215 UTC.


Gulf of Tehuantepec Gale Warning: Gale force winds are present 
across the Tehuantepec area as clearly depicted by an earlier 
ASCAT scatterometer passes. These gale force winds are supported 
by 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 04N along 82W continuing northward along
the Costa Rica/Panama border and offshore of the Caribbean coast
of Nicaragua in the SW Caribbean Sea, moving W at 10 to 15 kt. 
Associated convection has diminished during the past several


The monsoon trough axis extends from 10N74W to 10N90W to 11N114W
to low pressure near 10N118W to 10N120W. The intertropical
convergence zone axis extends from 10N120W to 08N126W to 11N140W.
Scattered moderate and isolated strong convection is from 07N to
11N between 92W and 95W, from 07N to 10N between 105W and 111W, 
and within an area bounded by 13N122W to 13N118W to 07N114W to 
07N128W to 13N122W.



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, 
with the pressure gradient between it and troughing along the 
eastern part of Baja California bringing 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 late 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 the 8 to 15 ft range. Also on Friday evening, 
NW winds will increase to fresh over the waters adjacent to Baja
California Norte.

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.


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 today through Wednesday, subsiding to 6 to 8 ft Wednesday 
evening and to 5 to 6 ft 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 6 to
8 ft on Friday.


Low pressure of 1013 mb near 24N128W continues to rapidly weaken
under very strong W to SW upper winds. Latest satellite imagery 
shows the low level center exposed and elongated with no deep 
convection present. Winds are 20 kt or less with the low, 
however, some residual seas to 8 ft in mixed swell persist 
within 150 nm in the N quadrant of the low as sampled by recent 
altimeter passes. This low will dissipate into a trough by late 
tonight with associated seas subsiding to less than 8 ft by then.

A 1009 mb low pressure area is over the W central waters near 
16N140W. Associated winds are moderate to fresh with some seas 
to 8 ft mainly NW swell on the E side of the low. This feature 
will move W of 140W through tonight with associated conditions E 
of 140W subsiding t less than 8 ft by early Wednesday.

Elsewhere, gentle to moderate winds are noted across the 
northern forecast waters under the influence of a weak ridge. 
Seas continue to subside across the S central waters, with an 
area of 8 to 9 ft seas in mixed swell. The mixed swell is 
forecast to gradually decay through the end of the week, however 
a new batch of SW swell is forecast by Wave model guidance to 
propagate through the far southern waters beginning on Thursday 
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 02:21:52 UTC