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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 012204

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Sat Oct 1 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 1800 UTC surface analysis and satellite imagery through
2145 UTC.


The Monsoon Trough axis extends from 09N85W to 09N96W to 10N102W
to 13N110W. It resumes at 11N122W to low pressure near 09N140W
1010 mb. Scattered moderate isolated strong convection is within 
120 nm south of the axis between 125W and 131W, and also within 
120 nm north of the axis west of 138W. Scattered moderate convection
is within 120 nm south of the axis between 89W and 91W, and
within 670 nm of the axis between 80W and 84W. Similar activity 
is seen north of the trough axis within 30 nm of a line from
12N96W to 12N101W.



A weak pressure gradient remains over the forecast waters, and is
supporting mainly light to gentle northwesterly winds across
much of the area. Northerly winds pulsed to around 30 kt late
last night into this this morning across the Gulf of Tehuantepec
with seas of 8-10 ft. Since 15Z this morning, these winds have 
diminished to the moderate to fresh range with seas now having
lowered to 8 ft based on a recent altimeter pass. Strong northerly
winds are forecast to materialize again late tonight, and into
early Sunday morning through the Gulf in a narrow swath as high
pressure over northeast and central Mexico ridges slightly
southward, and interacts with broad low pressure south of the
Gulf of Tehuantepec. These winds will diminish on Sunday
afternoon, then are expected to pulse back up again to strong
northerly winds late Sunday night, and diminish on Monday

A surface trough extends from 21N116W to low pressure near
18N115W 1011 mb to 15N113W. An Ascat pass from this afternoon
showed a weak cyclonic circulation consisting of gentle to
moderate winds, about 300 nm in diameter, associated with the low.
Seas are generally 5-6 ft outside the Gulf of California, and 2 ft
or less across all but the southern entrance to the Gulf of
California. The surface trough and low will continue to slowly
move westward through Sunday, then west-southwest as a dissipating
trough through Monday evening. While this takes place, the sub-
tropical ridge that presently extends from northwest to southeast
across the northwest and north-central waters will build east-
southeast and strengthen. This will tighten the pressure gradient
just north of the far northeast waters through by Monday with
northwest to north strong to near gale force winds just north of
30N. Northwest to north swell originating from north of 30N will
propagate as far south as 26N from between Baja California Norte
and 121W by Monday with resultant seas building to 9 ft.


Light and variable winds are expected north of the monsoon
trough, while gentle to locally moderate south to southwesterly
winds are expected south of the monsoon trough through Monday.
Combined seas of 4 to 7 ft, primarily in long-period southwesterly
swell is expected across the offshore waters into early next


A large upper anticyclone dominates the area east of 135W, while
broad upper troughing is over the area west of 135W. As stated
above, the aforementioned sub-tropical ridge will strengthen over
the northern portion through Monday. The pressure gradient between
the ridge and lower pressure within the monsoon trough region will
tighten.This will freshen winds north of the monsoon trough early
next week, with winds increasing to moderate to fresh category
from 15N to 25N west of about 120W. The long fetch of these fresh
trades will help build seas to the 7-9 ft from Sunday afternoon
into Monday.