000
AXPZ20 KNHC 210931
TWDEP 

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
931 UTC Wed Dec 21 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
0900 UTC.

...SPECIAL FEATURES...

Gulf of Tehuantepec: A gale warning remains in effect as a very
tight pressure gradient continues between 1029 mb high pressure
located over eastern Mexico near 23.5N99W and lower pressures
found near southeast Mexico. In addition, a stationary front
remains to the north of the area over the southwest Gulf of Mexico
with cooler and drier air continuing to be funneled through the
Chivela Pass southward. A recent ASCAT scatterometer pass measured
30 to 40 kt winds across the Gulf of Tehuantepec, and seas are
forecast to be 12 to 18 ft across the area. Winds should very
gradually diminish as continuous cold air advection over the
western Gulf is likely to reinforce the Tehuantepec event through
Friday. Gale conditions should likely diminish Saturday as the
surface winds switch to southerly over the western Gulf of Mexico.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...  

The monsoon trough axis extends from 09N83W to 05N97W. The
intertropical convergence zone axis extends from 05N97W to
11N119W, where it is disrupted by an embedded trough from 14N120W
to 08N126W, then resumes from 11N123W to 07N140W. Scattered
moderate convection is from 08N to 11N between 114W and 116W, and
also from 07N to 11N between 121W and 128W near the trough.

...DISCUSSION...   

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

Gulf of California: A recent ASCAT-B scatterometer pass indicated
fresh to strong northwest to north flow from 26N to 28N west of
110W in the central Gulf. These winds are a continuation of a
tight pressure gradient across the area which is in the process of
relaxing. The winds are now diminishing to 20 kt or less.

A strong upper-level cutoff low has induced a developing surface
low of 1012 mb near 22.5N118W, with a trough extending from
26N118W to 17N117W. Associated scattered moderate and isolated
convection can be found from 18N to 24N, within 210 nm east of the
trough axis. Recent ASCAT scatterometer passes just missed the
area east of the trough axis where fresh to strong winds are
likely. A recent altimeter pass did measure seas of 8 to 10 ft
east of the axis. These conditions should diminish by early
Thursday as the low and trough move to the northwest to north,
with the low reaching 30N119.5W by late tonight into early
Thursday.

On Saturday, southerly winds ahead of a cold front may reach a
fresh to near gale force breeze in the northern Gulf of
California. The cold front will be moving across forecast zones
PMZ009, PMZ011, and PMZ013 Saturday and Saturday night. The
northwest swell associated with the cold front could produce seas
of 11 to 14 ft on Saturday and Sunday.
  
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND
WITHIN 750 NM OF ECUADOR...

Gulf of Papagayo: Fresh to strong northeast winds are expected
to pulse in and downstream of the Gulf of Papagayo to near 90W
during the overnight and early morning hours through Saturday
night, with the assistance of the nocturnal drainage flow.
Locally, these winds will produce up to 8 ft seas. The fresh
northeast swells will merge with a Gulf of Tehuantepec gap wind
event to provide a large area of 8 to 12 ft seas downstream of the
gap regions.

Elsewhere across the region, winds will remain 20 kt or less,
with seas below 8 ft through Sunday night.

REMAINDER OF THE AREA...

A 1030 mb high centered north of the area near 33N139W along with
an embedded ITCZ surface trough from 14N120W to 08N126W support a
broad area of fresh to strong trades from roughly 07N to 21N west
of 133W. Seas of 8 to 11 ft in mixed wind waves and northwest swell
cover the majority of the waters north of the ITCZ west of 120W.
The high center is forecast to weaken over the next few days. As a
result, the aerial coverage of fresh to strong winds will decrease
through the day today, and remain limited through Sunday.

A cold front is forecast to drop south into the northern waters
Friday night with a brief surge of fresh to near gale northerly
winds possible behind it north of 28N. Large northwest swells,
building seas up to about 14 ft along 30N, will arrive behind the
front by early Saturday. New high pressure will build in behind
the front Saturday night through Sunday, with the next cold front
approaching from the north by late Sunday.
  
$$
LEWITSKY