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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 182113

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1858 UTC Tue Sep 18 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. 


The elongated area of low pressure currently centered SW of Cabo
San Lucas near 20N112W is expected to organize slowly and start 
tracking NNE tonight to reach central Baja early on Thu. Fresh to
locally strong winds and building seas to 8 ft are forecast for 
the southern and central Gulf of California starting Wed evening.
Winds and seas in this portion of the Gulf will continue through
Thu as the low/possible tropical cyclone passes inland over 
interior Mexico from the Gulf of California or dissipates. As 
indicated in the latest Tropical Weather Outlook, although 
environmental conditions appear conducive for tropical cyclone 
formation, the large size of the system and possible land 
interaction should prevent any significant or rapid development 
from occurring during the next two days. However, there is still 
a medium chance of this system becoming a tropical depression 
Wednesday or Thursday. Regardless of development, this broad 
disturbance will likely produce very heavy rainfall over Baja 
California Sur later this week. 


The monsoon trough axis extends from low pres 1006 mb over 
northern Colombia near 08N74W to 11N90W to 09N104W to 11N111W, 
then resumes from 13N125W to 11N132W to 11N136W. The ITCZ 
continues from 11N136W to beyond 11N140W. Scattered moderate 
isolated strong convection is present from 02N to 07N E of 80W, 
from 10N to 13N between 89W and 92W, from 13N to 15N between 95W 
and 101W and from 06N to 12N between 106W and 110W. Scattered 
moderate convection is seen from 10N to 12N W of 130W.



A surface trough over the Baja Peninsula will maintain light to 
moderate winds over the Gulf of California through this 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 and southern Gulf of California as a low pressure or 
possible tropical cyclone traverses the area Thu. See the 
Special Features section above for further details.

Building pressure to the NW is generating fresh winds W of Baja 
California Norte continuing through Wed morning. On the other 
hand, N swell will cause seas to build to just above 8 ft 
generally N of 27N between 118W and 127W tonight through Thu 
night. Otherwise, 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 tonight. 

A trough over the western Caribbean is inducing a gap wind event
over the Gulf of Tehuantepec. The event is expected to peak 
tonight at around 25 kt in concert with nocturnal drainage flow. 
Seas in this area are forecasted to top out around 8 ft. The 
trough will weaken and move NW into the Gulf of Mexico, which 
will allow this gap wind event to wind down. Otherwise, variable 
light to gentle winds will prevail elsewhere, with seas forecast 
to be in the 4 to 7 ft range.


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 arrive on the coast 
of Central America. A modest pulse of long period swell with up 
to a 20 second period is forecast to reach the coastal waters on
Wed morning. Seas are expected to be in the 5 to 7 ft range.


A tighter pressure gradient between a 1028 mb high centered NW 
of the area near 38N144W and the ITCZ supports fresh to strong 
winds from 12N to 22N west of 122W with seas to 9 ft. The center 
of high pressure is forecast to remain strong while it moves ESE 
but remains N of the area. This will sustain the fresh to strong 
winds in this region with seas up to 9 ft through Wed, then the 
high will begin to weaken as low pressure approaches it from the 

SW swell maintaining seas near 8 ft just S of the Equator and W 
of 105W are dispersing. This will allow seas in this region to 
subside below 8 ft by midday Thu. An area of seas associated with
low pres expected to form near 06N109W will develop on Wed, then
subside by Thu night as the SW swell disperse.

Finally, the center of low pressure located near 15N122W will 
continue to track WSW, accompanied by fresh to strong winds 
currently within 420 nm in the NW quadrant. Seas in this sector 
of the low will range between 8 to 9 ft. The low is forecast to 
weaken gradually tonight and Wed, allowing the associated winds 
and seas will subside.