Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 170931

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


Gulf of Tehuantepec Gale Warning: 
October marks the beginning of the Tehuantepec wind events. The
first gale-force event of a season typically occurs in mid-
October. Currently, gale force winds of 30 to 35 kt are noted
across the Tehuantepec area based on a recent ASCAT pass.
Building 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 cold front, located over the central Bay of
Campeche, supports this gap wind event. Winds are forecast to
further increase to 40 kt early this morning with seas building
to 14-15 ft. Gale force winds are expected to persist across the
Tehuantepec region through Wednesday night. Then, winds are
forecast to diminish below gale force early Thursday, but the gap
wind event will continue through the remainder of the forecast
period, with northerly winds of 20 to 30 kt and seas of 8 to 10
ft Thursday through early Friday morning.


The monsoon trough extends across Panama and Costa Rica to near 
09N85W to 08N95W to 08N102W. The ITCZ continues from 08N102W to 
09N108W to 08N120W to 11N130W to low pressure 1007 mb near 
14N136W to 11N140W. Scattered moderate convection is noted from 
08N to 10N between 95W and 103W. Scattered moderate isolated 
strong convection is within about 180 nm N of ITCZ axis between 
111W and 118W. Similar convection is near 11N136W.



Please see Special Features section above for information about
the Gulf of Tehuantepec. A surface ridge extends across the 
waters off Baja California producing gentle to moderate 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. By
late Friday a weakening cold front and accompanying large NW 
swell event will spread over the waters W of Baja California
building seas to 12-14 ft.

Winds have diminished below 20 kt over the northern and central 
Gulf of California as high pressure, previously located over the
Great Basin, moves eastward. A recent ASCAT pass indicates 
mainly moderate NW winds over this area. Expect mainly gentle to 
moderate NW-N winds across most of the Gulf of California 
through Wednesday, with light and variable winds on Thursday.


Moderate to fresh offshore winds will develop across the Papagayo
region each night through Thu night, with seas of 6 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 offshore waters of Guatemala 
and El Salvador, building seas to 8 to 10 ft today through 
Wednesday. Long period SW swells are forecast to reach the area 
between Ecuador and the Galapagos Islands late Thu into Fri, 
building seas to 7 to 8 ft on Fri.


A low pressure near 22N126W has weakened. Convection has become 
less organized and is being sheared away from the low level 
center. Winds of 20 to 25 kt are estimated to be occurring within
120 NM in the NE semicircle of the low with seas of 8-10 ft 
based on altimeter data. This low will degenerate into a trough 
late tonight into Wednesday.

A 1007 mb low pressure embedded in the ITCZ region near 14N136W 
is producing winds of 20 to 25 kt with seas of 8 to 9 ft based on
altimeter data. This low will also open up into a trough by 
tonight as it moves westward, reaching near 140W. 

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 south-central waters, and
currently seas of 8-9 ft are noted mainly S of 10N between 105W 
and 135W. By tonight, seas of 5 to 7 ft will dominate much of 
the waters W of 110W.

Looking ahead...a cold front is forecast by the NWP 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 by early Friday, 
spreading across all the northern waters W of 115W, and across
the west-central waters by late Friday night.


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Page last modified: Tuesday, 17-Oct-2017 09:31:20 UTC