AXPZ20 KNHC 180914
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
914 UTC Tue Dec 18 2018
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 0600 UTC surface analysis and satellite imagery through
Gulf of Tehuantepec Gale Warning: A scatterometer satellite pass
from 0318 UTC showed gap winds were still reaching 35 kt into
the Gulf of Tehuantepec, between high pressure north of the area
and relatively lower pressure over the eastern Pacific. The high
pressure is moving eastward, allowing gap winds into the Gulf of
Tehuantepec to finally diminish below gale force early this
morning. Winds will diminish further to below 20 kt by late
today, as seas subside from 11 to ft less than 8 ft. Light to
gentle breezes will persist into Thu, followed by another gale
event by late Thu as a strong cold front pushes across the Gulf
of Mexico north of the area. Strong gales with seas reaching as
high as 18 ft will persist through late Fri and early Sat before
gradually diminishing. Please refer to the latest high seas
forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more
specific marine related details.
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
No monsoon trough is observed. A weak trough extends from 06N95W
to 07N120W to 09N140W. Scattered moderate convection is noted
from 05N to 08N between 108W and 113W.
OFFSHORE WATERS WITHIN 250 NM OF MEXICO...
A trough reaching from 32N118W to 27N127W is sliding eastward
across the northern waters toward Baja California Norte. The
front will become diffuse through early today, and be followed by
moderate high pressure and freshening northerly winds across the
offshore waters. This pattern will prevail through early Wed
before the ridge begins to weaken. Also accompanying the front is
very large NW swell, with the leading edge of 12 ft seas or
greater impacting the northern coast of Baja California Norte.
Seas of 12 ft or greater in NW swell will reach the length of the
coast of Baja California Sur and the Revillagigedo Islands by
this afternoon. Swell of this size and period will produce
hazardous seas for mariners, and create very large and powerful
surf along the Pacific reefs and beaches. This high surf will
also produce coastal flooding and beach erosion in many exposed
locations from southern California to western Mexico.
This swell will decay to 8 to 10 ft by late Wed, just ahead of
another round of NW swell to 12 ft reaching Guadalupe Island and
the northern coast of Baja California by late Thu. This swell
will also decay below 12 ft rapidly, leaving 8 to 10 ft NW swell
in place for the Mexican open waters west of 105W through Sat.
Across the Gulf of California, strong high pressure will build
over the Great Basin by Wed. The high will support fresh to
strong winds across the northern and central Gulf Wed through
Thu, while seas build to 5- 8 ft.
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...
The pressure gradient between a wedge of high pressure extending
from the Caribbean over Central America and lower pressure over
the eastern Pacific will continue to support fresh to strong gap
winds across Papagayo and other typical gap wind zones of
central America until tonight, then winds will slacken as the
high over the Caribbean shifts E.
Farther south, fresh to strong trade winds across the southwest
Caribbean will support fresh gap winds over the Gulf of Panama
through tonight. Winds during this time frame could possibly
pulse to strong off the Azuero Peninsula.
Elsewhere, gentle to moderate winds will persist on either side
of the monsoon trough through early next week, as seas remain in
the 4 to 6 ft range.
REMAINDER OF THE AREA...
An upper-level trough extending from northern Baja California
Norte to 10N135W is supporting a persistent surface trough along
roughly 132W from 06N to 17N. The combination of lower level
trade wind convergence and divergence aloft on the east side of
the upper trough is supporting scattered convection from 13N to
16N between 113W and 117W.
Farther N, a 1025 mb high is centered along 31N130W, behind the
trough approaching Baja California Norte. This high will meander
about this area for the next few days and maintain a modest
pressure gradient to the south and southwest, to produce fresh to
locally strong NE to E tradewinds between 10N and 20N to the W
of 110W. Large NW swell moving through this area will produce
rough seas of 10-15 ft today before seas subside very slowly
An area of confused seas running 8 to 10 ft lingers in the area
from 02N to 15N between 93W and 112W. The seas in this area are
primarily a mix of NW swell with shorter period NE and E swell
from ongoing Mexican and Central American gap wind events. This
area will gradually diminish to 8 to 9 ft west of 100W by mid
week in predominantly NW swell as it merges with the larger area
of NW swell approaching from the west.