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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 260235

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
154 UTC Mon Sep 26 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 0000 UTC surface analysis and satellite imagery through
0230 UTC.


Tropical Depression Eighteen-E is near 16.7N 120.1W at 26/0230Z
or about 660 nm southwest of the southern tip of the Baja
California peninsula, moving north-northwest at 6 kt. Estimated
minimum central pressure is 1005 mb. Maximum sustained wind speed
is 30 kt with gusts 40 kt. Scattered moderate showers and
thunderstorms are active within 210 nm of the southeast semicircle
of the center of T.D. Eighteen-E. The depression is forecast to
intensify to tropical storm strength overnight and move within
180 nm to the west of Clarion Island Monday night before
weakening. See latest NHC forecast/advisory under AWIPS/WMO
headers WTPZ23 KNHC/TCMEP3 or visit the NHC website at for more details .


A tropical wave is located to the north of 09N along 97W/98W
drifting west. A weak surface low pressure area may be starting
to develop along the monsoon trough in the vicinity of the
tropical wave.

Another area of showers and thunderstorms has persisted over
western Panama and Costa Rica and the adjacent Pacific waters
over the past couple of days, propagating slowly westward.
Specifically, scattered moderate to isolated strong convection is
noted north of 05N between 82W and 86W off western Panama and
southwest Costa Rica. This may be evidence of another tropical
wave moving from the southwest Caribbean into the eastern Pacific.
Unlike the previous tropical wave, this tropical wave would be
fairly low latitude and is probably better defined in the lower to
mid levels of the atmosphere than at the surface. The main impact
will be persistent scattered to numerous showers and thunderstorms
over the next couple of days mainly east of 80W.


The monsoon trough extends from 11N86W to 10N112W. It resumes at
14N123W to 12N125W to 1011 mb low pressure near 12N139W to beyond
11N140W. Scattered moderate convection is within 60 nm south of
the monsoon trough axis between 92W and 100W and within 120 nm
south of axis between 135W and 140W.



The pressure gradient between relatively low pressure over
southern Arizona and northwest Sonora compared to strong high
pressure farther north over the Great Basin is contributing to the
potential for fresh eastern winds across the far northern Gulf of
California from late tonight through Monday, locally reaching 25
kt at times. Wave height development will be limited by fetch
however, and winds will diminish by late Monday. Elsewhere winds
and seas will remain fairly limited across the region through mid
week, except in areas beyond 200 nm off Baja California Sur that
will be impacted by increased winds and seas by mid week on the
periphery of the by then weakening T.D. Eighteen-E, tracking
mainly just outside of the offshore waters zones.

Farther south, a cold front is forecast to move across the Gulf
of Mexico waters early in the week. High pressure behind the
front will likely induce the first Gulf of Tehuantepec gap wind
event of the season with fairly weak pulse Tuesday night into
Wednesday morning followed by a strong pulse Wednesday night into
Thursday morning. At this time, marine guidance suggests
northerly winds of 20-25 kt and building seas to 8 ft by early


Mainly light and variable winds are noted north of the monsoon
trough while gentle to locally moderate south to southwest flow
is expected south of monsoon trough the middle of the week. Combined
seas of 3-6 ft, primarily in long-period southwest swell, are
expected through the middle of the week.


An area of low pressure located near 12N139W or about 1100 nm
east-southeast of the Big Island of Hawaii continues to produce
disorganized showers and thunderstorms. Satellite imagery
indicates scattered moderate convection within 90 nm in the
southeast quadrant of the center of the low pressure. Any
development of this disturbance should be slow to occur during the
next couple of days. After that time, environmental conditions
could become more conducive for development. This system is
expected to move west-northwestward during the next couple of
days, and then turn northward as it approaches the Central Pacific
basin. The pressure gradient between this low and the subtropical
ridge to the north is resulting in an area of fresh to strong
northeast from 13N-22N W of 130W. Persistent northeast swell is
allow combined seas to 9 ft north of the low pressure, from 13N to
17N west of 138W.