Tropical Weather Discussion
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AXPZ20 KNHC 170245

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
207 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
meteorological analysis.

Based on 0000 UTC surface analysis and satellite imagery through
0230 UTC.


Gulf of Tehuantepec Gale Warning:
An earlier 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 up to 30 KT
suggesting a gap wind event is in progress 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.


The monsoon trough extends across Central America near 09N85W to
08N92W, then transitions to the ITCZ near 09N105W and continues
to 09N115W to 13N130W to low pressure 1007 mb near 13N137W.
Scattered moderate and isolated strong convection was noted from
08N to 11N between 108W and 117W. Scattered moderate convection
was noted from 11N to 15N between 134W and 137W.



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.
An earlier 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.


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.


Low pressure near 22N125W has weakened and is no longer in the
Special Features section. Convection has become less organized
and is being sheared away from the low level center. Winds of 20
to 25 kt are estimated to be occurring within 150 NM in the N
semicircle of the low. A 1007 mb low embedded in the ITCZ
region near 13N137W 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 fresh winds and seas to 9 ft
through tonight. the low will degenerate into atrough on Thu
with winds and seas subsiding below High Seas criteria.

Elsewhere, 1029 MB high pressure located N of Hawaii has a ridge
axis that extends SE across the N waters to near 25N115W. 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 17 ft over the NW waters by early Friday,
spreading across all the northern waters by late Friday night.

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