Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 250952

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Sun Sep 25 2016

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
0945 UTC.


A broad and elongated area of low pressure continues within the
monsoon trough and is analyzed as 1006 mb low pressure near
14.5N120W. Scattered moderate isolated strong convection is
observed within 120 nm either side of a line from 16N113W to
16N119W to 12N124W where banding features becoming more
persistent. The pressure gradient is supporting strong winds
within about 90 nm of the low center surrounded by fresh winds
within 210 nm of the center, with seas of 8 to 12 ft.
Atmospheric and oceanic conditions are favorable for tropical
cyclone formation over the next several days. Even if it takes
longer for the convection to organize into persistent bands, the
pressure gradient is forecast to strengthen with minimal gale
winds developing tonight over the ne quadrant of the low
forecast near 16N119W. The low is forecast to move n reaching
near 18N118W on Mon night with seas gradually building to about
18 ft. There is uncertainty in the intensity and track, please
refer to the latest Graphical Tropical Weather Outlook for more
information at http://hurricanes.gov. 


A tropical wave is relocated to the n of 08N along 97W. Isolated
moderate and strong convection is observed within about 150 nm
either side of the wave axis. Expect the wave to gradually lose
identity over the next few days.  

A 1009 mb low pressure is embedded in the monsoon trough near 
12N137W. Scattered moderate isolated strong convection is noted 
within 45 nm either side of a line from 12N134W to 14N137W to
12N139W, but currently lacks persistent banding. The low is
forecast to move w to near 12N140W late tonight, then stall and
strengthen on Mon and Tue, then move ne and back into the area
near 15N140W on Wed night accompanied by at least strong winds.
Atmospheric and oceanic conditions will become more favorable
for tropical cyclone formation in 3 to 5 days.   


The monsoon trough extends w off the Pacific coast of northern
Costa Rica at 10N85W to 10N96w, then dips sw to 08N110W where it
loses identity. Scatterometer winds indicate that the monsoon
trough resumes just sw of the surface low at 14.5N120W, and
continues sw to 11N127W, then turns nw through the 1009 mb
surface low at 12N137W, and continues w to beyond 12N140W. 

Scattered moderate isolated strong convection is observed within
120 nm either side of a line from 04N77W to 08N82W, and within
30 nm either side of a line from 11N124W to 13N133W. Isolated
moderate and strong convection is noted elsewhere n of 05N
between 82W and 107W.   



A sub-tropical ridge axis extends from nw to se across the
offshore zones w of the Baja Peninsula terminating near 22N112W.
Gentle nw winds are observed w of the Baja Peninsula with little
change expected through Mon night, then the gradient should
relax supporting light n winds through early Wed. 

Gentle to occasionally moderate flow expected elsewhere along
the Pacific coast of Mexico today. Uncertainty begins tonight as
the tropical low previously described, moves northward and
begins to affect the w portion of offshore PMZ015, with gale
conditions forecast in that area on Tue and shifting n across
the far outer portion of PMZ013 on Wed night. Plenty of
uncertainty, so expect fluctuations in track and intensity
forecasts for the next few days. 

Fresh to occasionally strong nw winds are expected across the
northern Gulf of California through Mon morning, then the
gradient will relax supporting mostly moderate n flow through
Tue. Gentle to moderate n flow expected across the gulf waters
elsewhere n of 25N today, then light the gentle n flow beginning
on Mon night. Light and variable winds forecast s of 25N this

Guidance is hinting at a fairly strong cold front reaching the
sw Gulf of Mexico on Tue, resulting in strong drainage flow
across the Gulf of Tehuantepec beginning late Wed, and
increasing to near gale force late Wed night, and continuing
through Thu, with minimal gale conditions on Thu night.


Light to gentle southerly winds expected n of about 08N, while
gentle to locally moderate s to sw flow is expected s of 08N
through the middle of the week. Combined seas of 3 to 6 ft
primarily in mixing long-period sw and nw swell are expected
through the middle of the week.


The pressure gradient between the low previously described near
12N137W and the subtropical ridge to the n, will maintain fresh
ne trades, and combined seas of 6 to 9 ft, across the discussion
waters roughly from 13N to 23N between 130W and 140W today, with
these conditions gradually diminishing/subsiding from the ne to
20 kt or less, and seas less than 8 ft early Mon. 


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Page last modified: Sunday, 25-Sep-2016 09:53:09 UTC