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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 181604

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1439 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 1200 UTC surface analysis and satellite imagery through
1445 UTC. 


The broad area of low pressure currently centered SW of the Cabo
San Lucas is expected to organize slowly and remain nearly 
stationary until tonight, then will slowly develop and start 
tracking NNE to reach central Baja early on Thu. Fresh to 
locally strong winds and building seas to 9 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 the coast of northern 
Colombia near 12N73W to 09N79W to 10N86W to 11N90W to 09N104W to 
10N110W, then resumes from 14N123W to 11N136W. The ITCZ continues
from 11N136W to beyond 11N140W. Scattered moderate isolated 
strong convection is present within 150 nm of the coast of South 
America, Central America and Mexico between 77W and 100W, from 
07N to 12N between 105W and 110W and 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. 

Variable light to gentle winds will be elsewhere, except for 
moderate NE gap winds in the Gulf of Tehuantepec through Thu. 
Seas are 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 slightly tighter pressure gradient between a 1027 mb high 
centered northwest of the area near 37N145W and the ITCZ 
supports fresh winds from 12N to 22N west of 122W with seas to 9
ft. The center of high pressure is forecast to gradually 
strengthen 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 Thu afternoon.

Finally, the center of low pressure located near 16N121W will 
continue to track WSW, accompanied by fresh to strong winds 
mainly within 300 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 Fri and Sat, and the associated winds and seas 
will subside.