AXPZ20 KNHC 172135
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2137 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
Based on 1800 UTC surface analysis and satellite imagery through
Gulf of Tehuantepec Gale Warning: Gale force winds are present
across the Tehuantepec area as clearly depicted by recent 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
A tropical wave extends from 04N81W to 09N82W continuing
northward offshore of the Caribbean coast of Nicaragua in the SW
Caribbean Sea, moving W at 10 to 15 kt. Scattered moderate and
isolated strong convection is from 04N to 06N E of 79W to the
coast of Colombia. Scattered moderate convection is from 05N to
08N between 79W and 82W. Additional deep convection is in the SW
Caribbean westward across Costa Rica and SE Nicaragua.
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
The monsoon trough axis extends from 09N75W to 08N97W to
10N114W. The intertropical convergence zone axis extends from
10N114W to 08N124W to 12N137W. Scattered moderate and isolated
strong convection is from 07N to 10N between 91W and 95W, from
07N to 10N between 105W and 109W, and also within area bounded
by 12N123W to 12N114W to 07N114W to 07N127W to 12N123W.
OFFSHORE WATERS WITHIN 250 NM OF MEXICO...
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
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.
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...
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
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.
REMAINDER OF THE AREA...
Low pressure of 1014 mb near 24N127W continues to rapidly weaken
under very strong W to SW upper winds. A surface trough is just
to the W of the low extending from near 30N130W to 22N129W.
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 of 8 to 9 ft in
mixed swell persist within 180 nm in the NE semicircle of the low
as sampled by recent altimeter passes. This low will dissipate
into a trough late tonight with associated seas subsiding to less
than 8 ft by then.
A 1010 mb low pressure area is over the W central waters near
15.5N139W. Associated winds are moderate to fresh with some seas
to 8 ft mainly NW swell within 180 nm in the NE semicircle of the
low. This feature will move W of 140W through tonight with
associated conditions E of 140W subsiding to less than 8 ft.
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 within an area bounded by 15N112W
to 00N110W to 00N140W to 05N140W to 15N112W. The mixed swell is
forecast to gradually decay through the end of the week, however
a large 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