Tropical Weather Discussion
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000
AXPZ20 KNHC 162123
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2130 UTC Mon Oct 16 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 1800 UTC surface analysis and satellite imagery through
2115 UTC.

...SPECIAL FEATURES...

Gulf of Tehuantepec Gale Warning:
A 1550 UTC ASCAT pass indicated an area of 30 to 35 KT gale force
winds within 90 nm of the coast of Mexico from 20N to 25N as high
pressure is building over the eastern slopes of the Sierra Madre
Mountains in Mexico and the western Gulf of Mexico in the wake of
a strong cold front. Recent surface observations at Minatitlan
indicated strong northerly winds suggesting a gap wind event is
unfolding in the Gulf of Tehuantepec. Gridded forecast data
suggests winds have already reached gale force. The event is
forecast to peak in intensity later tonight through most of
Tuesday with winds possibly reaching 40 to 45 KT and seas
peaking at 10 to 15 FT. 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 25 KT and seas to 8 FT Thursday through Friday
night.

Low pressure of 1007 mb is centered near 21N124W. Shower and
thunderstorm activity is becoming increasingly displaced from
the low level center due to westerly shear. Currently scattered
moderate isolated strong convection is displaced between 90 and
240 NM in the NE quadrant of the low. Although the system
officially has medium chance for tropical cyclogenesis, the
window for this opportunity is rapidly closing as the system is
forecast to move west- northwestward or northwestward into less
conducive environmental conditions. Please refer to the latest
Tropical Weather Outlook for more information.

INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

The monsoon trough extends across Central America near 09N84W to
09N99W, where it transitions to the ITCZ that continues to
08N115W to 12N125W to 13N134W. The ITCZ then resumes west of low
pressure near 13N135W 1007 mb to near 10N140W. Scattered
moderate and isolated strong convection was noted from 05N to
09N E of 80W, from 08N to 12N between 106W and 113W, and from
10N to 16N between 131W and 137W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

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.

Broad high pressure over the central United States region is
supporting moderate to fresh northwest winds over the northern
and central Gulf of California, with seas nearing 4 to 5 ft.
A 1732 UTC ASCAT pass confirmed 20 KT winds over the Gulf of
California from 25N to 28N. The high pressure will then shift
eastward through Tuesday which will help to decrease winds over
the area.

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 the middle of the week, 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 in the
Gulf of Tehuantepec will reach the offshore waters of Guatemala
and El Salvador, building seas to 8 to 10 ft tonight through
Wednesday. By Thursday, a fresh batch of SW swell will increase
seas to 6 to 8 ft between Ecuador and the Galapagos Islands.

REMAINDER OF THE AREA...

Please see the Special Features section above for more information
on low pressure centered near 21N124W. A 1007 mb low embedded in
the ITCZ region near 13N135W is producing winds of 20 to 25 kt
as indicated by the edge of an afternoon scatterometer pass.
This low will likely continue to generate strong winds and seas
to 9 ft through tonight. Elsewhere, 1030 MB high pressure
located N of Hawaii has a ridge axis that extends SE across the N
waters to near 25N117W. Cross equatorial southwesterly swell
will continue to propagate across the south- central waters,
particularly S of 15N between 100W and 130W through late today,
with seas of 8 to 9 ft. The aereal extent of the 8 ft seas or
greater will diminish on Tuesday, and by Tuesday night, seas of 5
to 7 ft will dominate most 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 16 ft over the NW waters by late Thursday
night and Friday, spreading across all the northern waters by
Friday night.

$$
Cobb


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