AXPZ20 KNHC 150336
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Sat Dec 15 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 0000 UTC surface analysis and satellite imagery through
Gulf of Tehuantepec Gale Warning: Strong northerly winds have
increased to gale force across the Gulf of Tehuantepec north of
14.5N in the past few hours, associated with a cold front
crossing the central Gulf of Mexico this evening. Strong high
pressure behind this front will produce a further increase in
winds to strong gale force winds during the next few hours and
continue through early Sun. Computer model guidance suggests
that these gales will continue through the weekend and will last
until Mon afternoon. Peak winds are forecast to be around 40 kt
on Sat as corresponding seas quickly build to near 18 ft.
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
The monsoon trough extends from 09N72W TO 06N82W TO 06N104W. The
ITCZ continues from 06N104W TO 09N131W to beyond 08N140W.
Scattered moderate isolated strong convection is noted within
150 nm S of the trough between 77W and 86W, and from 05N to
11.5N between 125W and 137W.
OFFSHORE WATERS WITHIN 250 NM OF MEXICO...
Weak high pressure ridging SE from 32N122W to near 28N116W is
maintaining light to gentle breezes across the Pacific waters
off Baja California. Fresh NW flow continues over the Gulf of
California between 24N and 29N. Meanwhile the next pulse of long
period NW swell has entered the area from the west, and is
moving S of Baja California Sur this evening. NW swell will
dominate the offshore waters off the entire Baja California
coast through the Revillagigedo Islands with seas building up to
9 ft tonight, followed by reinforcing NW swell through Sun.
Looking ahead, a cold front will reach the northern coast of
Baja California by Mon night, accompanied by large reinforcing
NW swell, bringing seas of 12 to 18 ft to all of the offshore
zones of Baja California and into the Revillagigedo Islands by
late Tue. Swell of this size and period will present hazardous
seas for mariners, cause very powerful and dangerous surf along
the Pacific reefs and beaches, and likely produce areas of
modest coastal flooding and beach erosion.
A mid to upper-level disturbance is approaching the area from
the west. This disturbance is currently interacting with a
surface trough extending from 09N133W TO 17N127W. The
disturbance is producing scattered moderate convection from 14N
to 23N between 117W and 127W, and is expected to shift NE
through the weekend. This may bring a few showers to the central
and southern portions of the Baja California Peninsula and Gulf
of California late tonight through Sun.
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...
Gulf of Papagayo...Fresh gap winds will pulse to around 20 kt
tonight before ramping back up to between fresh and strong
during the overnight and early morning hours Sat night. These
conditions will then persist through Mon night as high pressure
builds north of the region. Seas are expected to max out near 10
ft Sun morning.
Gulf of Panama...Fresh northerly winds across and downstream of
the Gulf will slowly diminish through Sat, then become fresh
from the north Sat night through Tue.
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...
Weak ridging prevails across the NE waters off of Baja
California. A persistent surface trough extends from 09N133W TO
17N127W. Afternoon scatterometer data indicated fresh to strong
winds on the W side of the trough between 11N and 19N, and east
of the trough to 125W from 16N to 19N. The high pressure ridge
to the N will weaken through tonight ahead of an approaching
cold front, allowing the winds to diminish to between moderate
and fresh by Sat morning.
A weakening cold front crossing the NW portion of the discussion
area extends from 30N132W TO 25.5N140W, and is introducing a new
round of NW swell with seas of 11 to 15 ft following the front.
The front will slow forward motion then dissipate through Sat,
with the swell propagating ahead of the front and slowly
subsiding. Elsewhere NW swell in excess of 8 ft will more or
less dominate the waters west of 110W through Sun. A stronger
cold front will usher in very large NW swell, in excess of 20
ft, which will enter NW portions of the forecast area early Sun.
Seas of 12 ft or higher could encompass almost all of the
forecast waters N of 07N and W of 115W by Tue morning.