Tropical Weather Discussion
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000
AXPZ20 KNHC 181002
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Wed Jan 18 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
0930 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

A meandering trough extends from 05N77W TO 02N79W to 03N90W. The
ITCZ axis extends from low pressure near 05N93W 1012 mb to 03N103W
to 03N110W to 08N118W where it briefly ends. It resumes at
08N122W to 06N130W to 05N140W. Scattered moderate isolated
strong convection is seen within 180 to 240 nm north of the axis
between 112W and 118W, and also within 60 nm north of the axis
between 122W and 127W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

Satellite water vapor imagery shows an upper level trough
extending from a deep layered cut-off low pressure system across
the central portion of SW New Mexico southwestward to far NW
Mexico, and continuing to across Baja California Norte and to
beyond 19N120W. An upper level jetstream branch is moving through
the base of this trough from 18N120W northeast to 24N110W and to
over west-central Mexico at 25.5N108W. It continues well inland
to over much of northern Mexico and into SE Texas. The imagery
depicts a 450 nm wide moisture plume consisting of mid and upper
level clouds located to the southeast of the jet stream branch.
The strong southwest jet stream winds are advecting these clouds
northeastward towards much of central Mexico. Jetstream energy is
sufficiently available, and will combine with the deep moisture
to produce scattered showers and isolated thunderstorms offshore
the Mexican coast from near Manzanillo north to just south of
Baja California Sur and the coast of Mexico near Los Mochis.
Similar activity is very possible inland the Mexican coast
between these two locations to well inland across the Sierra
Madre Occidental mountains.

Gentle to moderate northwest to north winds prevail off the
coast of Baja California and in the Gulf of California per
the Ascat pass from 0514Z, and from a couple of ship
observations noted along the ocean side of the Baja California
coast. Light to gentle northerly winds prevail south and east of
Acapulco. Seas across the area are running 5-6 ft west of Baja
California, 1-3 ft in the Gulf of California, and 3-5 ft
elsewhere.

Global models indicate a cold front will move into the waters
off Baja California Norte Thursday, then become diffuse ahead of
a much stronger cold front that will quickly move in across Baja
California and the Gulf of California Friday and Saturday. The
second cold front will be accompanied by fresh to strong winds
and large northwest swell. This swell event is expected to build
seas to the range of 12-19 ft in the waters off Baja California
Norte Saturday, and 8-13 ft seas off Baja California Sur.
Wave model guidance actually indicates that seas may max out
higher to around 21 ft in the waters north of 29.5N on Saturday.
These marine conditions are likely to bring hazardous marine
conditions to mariners navigating the nearshore and coastal
waters, and very dangerous surf conditions along the coasts and
beaches. Southwest winds ahead of the second cold front are
expected to increase to near gale force over much of the northern
portion of the Gulf of California Friday night into Saturday,
with seas possibly building to 8-9 ft, quite impressive for those
waters.

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...

Moderate northwest winds this afternoon will pulse to 25 kt late
tonight through Wednesday morning, and then again briefly late
Wednesday night across the Gulf of Papagayo and downwind to
about 89W. Winds area then expected to diminish by Thursday
night. Light to gentle variable winds are expected there Friday.

Light to gentle easterly winds will prevail elsewhere through
Saturday. Seas will be generally 3-5 ft in the forecast waters.

REMAINDER OF THE AREA...

A 1024 mb high pressure centered at 26.5N135W extends a ridge
southeast to the vicinity of Cabo Corrientes. The gradient
between this high and lower pressure associated with the ITCZ is
supporting an area of fresh to strong northeast trade winds from
10N TO 16N west of 130W and from 12N to 14N between 122W and
133W, with seas in the range of 9-11 ft. Fresh trades are found
elsewhere roughly from 07N to 19N west of 133W, and from 10N to
15N between 116W and 133W per the 0510Z Ascat pass. Seas with
these trades are in the 8-10 ft range due to mixed northwest
swell with northeast windwaves. Fresh trades will remain from 07N
to 20N west of 122W, with 8-10 ft seas in mixed NE and NW swell.
The 1024 mb high will be nudged to the southwest over the next
few days in response to the aforementioned cold fronts forecast
to pass across the waters north of 25N. This will allow for the
zone of the strong trades to decrease in coverage and shift
westward through Friday.

As mentioned above, a very active jet stream branch is rounding
the base of the deep layered trough across northwest Mexico. The
upper trough will continue to slide eastward through Friday while
shearing out, however a stronger trough will quickly sweep
southeastward, and merge into the first trough on Thursday. High
pressure will build eastward behind the previously mentioned
cold fronts, with associated moisture and weather shifting
eastward with it.

Looking ahead, northwest swell with seas to 8-16 ft associated
with a cold front moving eastward across the waters north of 25N
through Thursday will be followed by a second front expected to
sweep southeastward across the northern waters Thursday night
and Friday. Wave model guidance shows large northwest swell will
propagate southeastward into the waters north of 20N behind the
second front, with seas building quite large to 15-21 ft in the
far northern waters east of 130W late Friday into Saturday.

$$
AGUIRRE



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