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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 110905

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Tue Dec 11 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 0600 UTC surface analysis and satellite imagery through 
0900 UTC.


Gulf of Tehuantepec Gale Warning: A tight pressure gradient over 
the Isthmus of Tehuantepec is producing a large area of strong 
gales across the Gulf of Tehuantepec. A scatterometer pass at 
0400 UTC showed 40-45 kt winds extending from 16N95W to 14N95.5W 
and 30-40 kt winds between 94W and 97W north of 12.5N. The large 
area of strong gales will generate very large seas to 21 ft for 
the next several hours. Gale force winds will continue today and 
tonight, then rapidly decrease and become gentle to moderate by 
Wed evening as high pressure over the Gulf of Mexico weakens and 
shifts east. Large N to NE swell will propagate well away from 
the source region, with the leading edge of 8 ft seas expected 
to reach to 110W and 02N by early Wed, and merge with a larger 
area of 8 ft seas approaching from the northwest. Please refer 
to the Eastern Pacific High Seas Forecast under AWIPS/WMO 
headers HSFEP2/FZPN03 KNHC for more specific marine details.


The monsoon trough is analyzed from 05N77W to 04N91W. The ITCZ 
extends from 04N91W to 08N108W to 08N119W. The ITCZ resumes west 
of a surface trough from 08N124W to 07N140W. Scattered moderate 
isolated strong convection is occurring from 07N to 10N between 
116W and 131W.



Gulf of Tehuantepec...After the ongoing high wind event tapers 
off on Wed, light to gentle winds are expected through Thu 
night. A strong cold front moving into the Gulf of Mexico will 
initiate another gale force wind event Fri and Sat. 

High pressure NW of the area extends a ridge southeast to the 
Revillagigedo Islands. The pressure gradient between the high 
and troughing in the Gulf of California is supporting gentle to 
moderate NW winds across the entire Gulf of California. Model 
guidance suggests that the gradient will tighten early Thu, with 
fresh to strong winds expected over almost all of the Gulf of 
California through Fri morning.

5 to 9 ft seas west of Baja California will spread eastward 
through tonight, then subside below 8 ft through Wed evening.


Gulf of Papagayo...Winds will pulse to near gale force tonight, 
remain fresh to strong Wed night, then diminish to 10-15 kt Thu.

Elsewhere, gentle to moderate winds will persist on either side 
of a weakening monsoon trough, with seas in the 4-6 ft range.


A weakening cold front extends from 31N121W to 25N134W. NW swell 
associated with the front supports seas in excess of 8 ft across 
most of the area west of 120W. A tighter pressure gradient that 
will build east-southeast behind the front will support fresh to 
strong NE trade winds from 08N to 27N west of 128W through Thu.

Wave model guidance suggests a rather large area of 8 ft seas 
will stretch from about 02N to 15N between 92W and 110W as a 
result of long-period northwest swell mixing with shorter period 
northeast swell from the Gulf of Tehuantepec, and to a lesser 
extent those from the Gulf of Papagayo. This area of swell will 
merge into a larger area of seas associated with northwest swell 
which will cover most of the forecast area west of 92W on Wed. 

A surface trough is analyzed from 15N120W to 07N122W. Associated 
winds are moderate to fresh, with seas to 8 ft. The trough is E 
of a pronounced upper-level trough as seen in water vapor. The 
upper trough will amplify southward, but the surface trough will 
gradually loses its identity and continue westward.