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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 170944

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
944 UTC Thu Jan 17 2019

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 0600 UTC surface analysis and satellite imagery through
0900 UTC.


A trough extends from 05N77W to 04N80W. The intertropical
convergence zone continues from 04N80W to 03N100W to 1011 mb low
pressure near 07N110W to beyond 07N140W. Scattered moderate
thunderstorms is noted within 90 nm in the east quadrant of the 
low pressure. Elsewhere scattered moderate thunderstorms are
observed from 11N to 13N between 110W and 115W.



Strong to near-gale force winds are pulsing through the Gulf of 
Tehuantepec, supporting 8 to 10 ft seas. These pulses will 
continue into Fri then diminish as the gradient weakens across 
the region. Fairly tranquil conditions will persist across the 
Gulf of Tehuantepec and downstream late Fri through late Sat. The
pattern will change abruptly Sat night, as a the leading edge of
a very strong cold front moves through southern Mexico, across 
the isthmus of Tehuantepec and into the adjacent waters of the 
Gulf of Tehuantepec. As high pressure builds behind the front 
over east central Mexico, and the bulk of the cold air reaches 
the southern Gulf of Mexico, the initial gale force winds will 
intensify to a strong gale into Sun morning, possibly reaching 
minimal storm force. Seas will build accordingly, reaching as 
high as 24 ft by midday Sun. Meanwhile, a large plume of 25 to 35
kt and seas in excess of 12 ft will push as far as 420 nm to the
south-southwest downstream of the Gulf of Tehuantepec. Strong 
gales will likely persist thereafter into Mon. Marine interests 
transiting through the Gulf of Tehuantepec Sun into early next 
week should be aware of this upcoming gap wind event, and take 
necessary action to avoid hazardous marine conditions over the 
affected waters.

Elsewhere over Mexican offshore waters outside of 
Tehuantepec...1023 mb high pressure west of Baja California near
28N119W continues to maintain light to gentle breezes across the
region north of 25N and gentle to moderate breezes elsewhere. NW
swell of 8 to 9 ft persist over open waters beyond 120 nm north 
of Cabo Corrientes. A weak cold front will move into into 
northern Baja California Norte this evening. While the front will
dissipate as it moves across Baja California and the Gulf of 
California through Fri, it will be accompanied by a new round 
long-period NW swell of 12 to 16 ft across the waters off Baja 
California. High pressure building behind the front will allow 
fresh to strong NW winds north of Cabo San Lucas late Fri into 

Over the Gulf of California, strong high pressure building over
the Great Basin north of the area will support fresh to strong 
NW winds extending the length of the Gulf from Fri night through
Sat. The strength, fetch and duration of the winds will be
enough to support wave heights to 8 ft in the southern Gulf of
California by Sat night. Winds and seas will diminish by Sun as
the high pressure weakens and shifts east.


Strong high pressure north of the area will keep gap wind areas
active through Fri and Sat. Fresh to strong gap winds persist as
far as 300 nm to the W-SW of the Gulf of Papagayo through the 
next several days. Winds will occasionally pulse to near-gale 
force during overnight and early morning hours. Seas will build 
to 8 to 10 ft. Similarly fresh to strong northerly gap winds will
impact mainly the western Gulf of Panama extending into the
waters south of the Azuero peninsula.

These gap winds will diminish Sat and Sat night as the high
pressure north of the region supporting them shifts eastward
ahead of a strong cold front. New high pressure will build in the
wake of the front, supporting another round of even stronger gap
winds through the Gulfs of Papagayo and Panama. Winds to gale
force are possible through the Gulf of Papagayo Mon night.


1009 mb low pressure is centered along the ITCZ near 07N111W
moving west at 10 to 15 kt. Observations from a nearby TOGA-TAO 
buoy along with data from an earlier scatterometer pass showed 
fresh to strong winds within 90 nm in the northern semicircle of 
the low pressure. An altimeter satellite pass from 05 UTC 
confirmed seas as high as 13 ft in the area of strong winds north
of the low pressure. Scattered thunderstorms are active within 
90 nm to the east of the low pressure. This is an indication the 
low pressure is experiencing strong westerly shear as it moves 
west of the upper trough axis that had been sustaining it over 
the past couple of days. The low will weaken through today, and 
open into a trough tonight as it reaches 115W. The trough will 
weaken further as it continues westward along the ITCZ over the 
next several days. 

Farther northwest, a weak cold front reaching from 30N130W to
28N140W will weaken through today as it continues to move
eastward across the waters north of 28N. The main impact will be
a new round of long-period heavy NW swell. An altimeter 
satellite pass from 0230 UTC showed seas of 15 to 23 ft behind 
the front entering the northwest portion of the discussion area 
near 30N140W. While the NW swell will subside somewhat through
today as it moves into the region, swell in excess of 12 ft will
reinforce existing NW swell of 8 to 10 ft farther south over 
waters west of 120W through Fri. 

An area of mixed swell will emerge roughly south of 15N between
95W and 100W, due to the reinforced NW swell, a component of SW 
swell, and shorter period NE and E swell originating out of the 
gap areas to the east. 

A ridge will build by Sat across the waters north of 25N in the 
wake of the front. This will support a broad area of fresh trade 
winds farther south into the tropics, with fresh to strong winds 
developing ahead of the surface trough moving along the ITCZ. The
ridge will weaken into Sun, allowing winds and seas to diminish 
somewhat across the tropics. Seas of 8 to 9 ft will persist
however Sun into next week south of 20N west of 135W in a mix of
NW swell and remaining windwaves from local trade winds.