AXPZ20 KNHC 161605

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Sun Dec 16 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
1545 UTC.


Gulf of Tehuantepec Gale Warning: The tight pressure gradient
over southeastern Mexico resulting from the combination of strong
high pressure over northern Mexico and lower pressure south of 
Mexico is bringing strong gale force northerly winds over the 
Gulf of Tehuantepec with seas to 18 ft. This strong gap wind 
event will continue through tonight, before diminishing on Mon 
as the strong high pressure over Mexico shifts eastward and 
weakens. Seas with this event will subside to 9 to 13 ft Mon and 
to less than 8 ft on Tue as the northerly winds diminish to fresh
speeds. Please refer to the latest high seas forecast issued 
under AWIPS/WMO headers HSFEP2/FZPN03 for more specific marine 
related details. 


The monsoon trough axis extends from 07N78W to 06N88W, where 
latest scatterometer data indicated that it transitions to the 
ITCZ and continues to 04N110W to 07N118W to 08N130W to 09N140W.
Scattered moderate convection is within 30 nm either side of
ITCZ between 116W and 121W.



A weak ridge will prevail over the area maintaining light to 
gentle breezes across the area. Northwest swell with seas to 9 ft
will continue in the offshore waters of Baja California through 
this evening before subsiding to 8 ft late tonight. 

A cold front will approach the region Mon bringing a new set of 
northwest swell, with seas from 12 to 17 ft reaching the 
northern coast of Baja California Norte and Guadalupe Island. 
Swell of 12 to 15 ft will cover the Baja offshore waters to the 
Revillagigedo Islands into Tue. Swell of this size and period 
could likely pose hazardous seas for mariners, while at the same 
time create very powerful and dangerous surf along the Pacific 
reefs and beaches, and is expected to produce coastal flooding 
and beach erosion in some locations.

Over the Gulf of California, strong high pressure north of region
have been supporting moderate to fresh breezes across the basin.
A mid to upper-level disturbance approaching the area from the 
west may bring a few showers to the central and southern 
portions of the Baja California Peninsula and Gulf of California 
toda and tonight. Strong high pressure will build north of the 
area by Wed, and will support fresh to strong winds across the 
northern and central gulf.


Gulf of Papagayo...Strong northeast winds through the Gulf this 
morning will become mainly fresh to strong by this evening. These
winds will continue into mid week, pulsing to strong during the 
overnight and early morning hours through Tue then to fresh
speeds through Wed. Seas with these winds are expected to be 8 
to 9 ft. Fresh winds will also pulse across the Gulf of Panama 
and Gulf of Fonseca through Mon night.

Elsewhere, gentle to moderate winds will persist on either side 
of the monsoon trough through early next week, as seas remain in 
the 4 to 6 ft range.


A broad mid to upper-level trough stretches from a mid to upper-
level low over far northern Baja California to 23N117W and to 
near 17N122W. A very strong jet stream branch rounds the base of
this trough and extends northeastward to over northwestern 
Mexico. The combined factors of upper-level divergence to the 
east and southeast of the trough and jet dynamics aloft in 
combination with trade wind convergence in the lower atmospheric 
levels are supporting scattered moderate convection north of the 
ITCZ to near 15N and between 125W and 130W. Areas of moderate 
rain with possible embedded isolated thunderstorms are evident 
from 15N to 21N between 115W, while mostly rain is possible from 
18N to 24N east of 115W to central and southern Baja California. 
Ascat data from overnight last night highlighted fresh to strong 
east winds near 13N130W. A concurrent altimeter satellite pass 
showed seas to 9 ft, likely mixed with northwest swell.

A cold front has moved into the northwest corner of discussion 
area. This front and move eastward across the waters north of 20N
through Mon afternoon while weakening. The main impact will be a
new set of northwest swell, with combined seas in excess of 
12 ft to as high as 22 ft propagating across most of the region 
north of 12N and west of 120W through late Mon. 

During the early to middle part of next week, the leading edge 
of this next round of northwest swell will mix with shorter 
period northeast and east swell emerging from the gap wind areas,
and possibly even southerly swell, to create an area of mixed 
seas west of about 107W.