Tropical Weather Discussion
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000
AXPZ20 KNHC 240945
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Sat Sep 24 2016

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
0945 UTC.

...SPECIAL FEATURES...

A broad and elongated area of low pressure continues within the
monsoon trough and is analyzed as 1007 mb low pressure at
12.5N118W. Scattered moderate isolated strong convection is
observed within 120 nm either side of a line from 11N117W to
15N120W where banding features appear to be developing. The
pressure gradient is supporting strong s to sw winds e of the
low center, within 120 nm either side of a line from 15N110W to
09N116W with seas of 8 to 11 ft. Atmospheric and oceanic
conditions are favorable for tropical cyclone formation over the
next several days. Even if it takes longer for the convection to
organize into persistent bands, the pressure gradient should
tighten with minimal gale winds developing on Sat night with the
low forecast near 16.5N116.5W. The low is forecast to move n
reaching near 18N117W on Sun night with seas gradually building
to about 15 ft. There will be plenty of uncertainty in the
intensity and track organization occurs. Please refer to the
latest Graphical Tropical Weather Outlook for more information
at http://hurricanes.gov.

...TROPICAL WAVES...

A tropical wave is analyzed n of 10N along 96W, and has been
progressing w at about 12 kt. Isolated moderate and strong
convection is observed within about 150 nm either side of the
wave axis. Expect the wave to gradually lose identity over the
next few days.

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

The monsoon trough extends sw off the Pacific coast at the
Nicaragua and El Salvador border at 13N88W to 10N100W to 13N107W
where it loses identity. Scatterometer winds indicate that the
monsoon trough resumes just w of the surface low at 12N118W, and
continues w through a 1009 mb surface low at 12N130W and
continues w to beyond 10N140W. Scattered moderate isolated
strong convection is observed well nw of the low pressure at
12N130W, roughly within 75 nm either side of a line from 15N129W
to 13N135W. Similar convection is observed within 120 nm either
side of a line from 10N91W to 11N103W, within 30 nm either side
of a line from 17N99W to 12N102W and elsewhere within 180 nm
either side of a line from 14N109W to 11N130W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

A sub-tropical ridge axis extends from nw to se across the
offshore zones w of the Baja Peninsula terminating at a fairly
sharp crest near 21N110W. Strong nw winds are observed from 30N
to 32N between 118W and 123W, with seas of 7 to 10 ft. Moderate
to fresh nw winds are observed elsewhere n of 24N within 250 nm
w of the Baja Peninsula with gentle n winds noted to the s of
24N. The pressure gradient is forecast to quickly relax today
with gentle nw to n flow expected w of the Baja Peninsula
through the remainder of the weekend.

A trough is barely noticeable across the southern Gulf of
California with moderate to locally fresh n winds across the
gulf waters n of 28N and light southerly winds s of 28N. Expect
strong n winds to develop across the gulf waters n of 30N late
tonight and persist through Sun night. Light and variable winds
expected elsewhere along the Pacific coast of Mexico primarily
to mixing long period s and nw swell. Uncertainty then increases
as the tropical low previously described, moves northward and
begins to affect offshore PMZ015 tonight, initially to the s of
19N between 112W and 116W, with the conditions deteriorating on
Sun and Mon as the gale center, or tropical cyclone, continues n
across the offshore waters w of the southern Baja Peninsula.
Plenty of uncertainty, so expect fluctuations in track and
intensity forecasts for the next few days.

Guidance is hinting at a fairly strong cold front reaching the
sw Gulf of Mexico on Tue, and reinforced on Wed, resulting in
strong to near gale flow across the Gulf of Tehuantepec on Wed
night and continuing into Fri.

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

Light to gentle e to se winds expected n of about 12N while
gentle to locally moderate s to sw flow is expected s of 12N
through the middle of the next week. Combined seas of 4 to 7 ft
will continue today primarily in mixing long-period sw and nw
swell, then subside to 3 to 5 ft on Sun and continuing into the
middle of next week.

REMAINDER OF THE AREA...

A 1009 mb low pressure area is analyzed along the monsoon trough
near 12N130W. Expect the low to move wnw to near 13N140W late
Sun. The pressure gradient between this low and the subtropical
ridge to the n will maintain fresh to strong ne trades, and
combined seas of 6 to 9 ft, across the discussion waters from
13N to 25N between 130W and 140W today, with these conditions
gradually diminishing/subsiding from the ne to 20 kt or less,
and seas less than 8 ft on Mon.

$$
Nelson



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