AXPZ20 KNHC 172121
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1845 UTC Mon Sep 17 2018

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
2045 UTC.

...SPECIAL FEATURE...

The low currently centered just S of the Revillagigedo Islands
will stay nearly stationary through Tue evening, then will start
tracking NNE and reach central Baja early on Thu. This system is
forecasted to remain weak during the next couple of days which
will allow the area of 8 ft seas in currently its vicinity to
subside tonight. Winds and seas on the E side of this system are
expected to reach advisory levels E of Baja California Sur Wed
and Wed night as the system gradually develops. Strong winds and
seas to 8 ft could affect the central Gulf of california Thu.
There is a medium chance of this system becoming a tropical
cyclone during the next 48 hours.

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

The monsoon trough axis extends from northern Colombia near
08N74W to 09N94W to 18N109W to low pressure 1007 mb centered near
17N114W to low pressure 1007 mb centered near 15N120W to low
pres 1009 mb near 09N140W. Numerous moderate and scattered strong
convection is seen within 90 nm of 15N121.5W. Scattered moderate
and isolated strong convection is found elsewhere within 240 nm
either side of a line from 19N105W to 14N124W. Scattered moderate
isolated strong convection is observed from 07N to 11N between
83W and 92W, from 07N to 11N between 99W and 106W and within 120
nm of the monsoon trough axis W of 135W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

A surface trough over the Baja Peninsula will maintain light to
moderate winds over the Gulf of California through Tue morning.
Afterwards, the winds are forecast to increase to moderate to
fresh speeds in response to a high pressure ridge building to the
NW. Winds over the gulf N of 29N are forecast to become strong
and from the S to SE early on Wed continuing through Thu
morning. Fresh to strong winds are then expected to develop
over the central Gulf of California as low pres traverses the
area Thu.

Building pressure to the NW will also generate fresh winds W of
Baja California Norte tonight through Wed morning with
corresponding seas to 8 ft. Pulses of long period SW swell will
continue to impact the entrance of the Gulf of California, and
the waters W of Baja California through Tue night. This same
ridge of high pressure will generate fresh to strong winds W of
California, which will generate NW swell. These swell will cause
seas to build to above 8 ft generally N of 27N between 119W and
129W Tue night through Thu night.

Monsoonal flow to the SE of a 1007 mb lows centered just S of
the Revillagigedo Islands near 18N114W and well to the SW of
these same islands near 15N120W is subsiding. This has allowed
seas in the offshore waters E of Cabo Corrientes to subside below
8 ft. Both lows will depart this area during the next several
days, thus allowing the current light wind regime to remain in
place in this area through the end of this week. The low
currently centered just S of the Revillagigedo Islands will stay
nearly stationary through Tue evening, then will start tracking
NNE and reach central Baja early on Thu. There is still a high
chance of this system on becoming a tropical cyclone within the
next 5 days.

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

The monsoon trough is expected to remain in the vicinity of 07N
to 12N during the next several days. Winds will be light to
gentle N of the trough and gentle to moderate S of the trough.

Cross-equatorial SW swell will continue to impact the coast of
Central America through Tue night followed by a modest pulse of
long period swell with up to a 20 second period reaching the
coastal waters on Wed morning. Seas are expected to be in the 5
to 7 ft range.

REMAINDER OF THE AREA...

The surface trough, remnant of Paul, has passed to the west of
the area. However, a tightening pressure gradient between this
feature and a 1021 mb high centered just north of the area near
31.5N138W supports fresh to strong east winds from 16N to 26N
west of 134W. Latest satellite-derived wind data indicates strong
winds in this region. Enhanced winds and seas in this area will
persist through Thu, then winds and seas will begin to subside.

Otherwise, the low currently centered SW of the Revillagigedo
Islands near 15N120W will continue to track WSW during the next
few days. The area of winds and seas associated with this low
will gradually expand and combine with the area of winds and seas
mentioned in the previous paragraph by late Tue night. This low
is forecast to weaken slowly Fri and Sat as the associated winds
and seas gradually subside.

$$
CAM

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