000
AXPZ20 KNHC 210345
TWDEP 

TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI DEC 21 2012

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
SCATTERED MODERATE FROM 95W TO 99W WITHIN 60 NM OF TROUGH.THE 
MONSOON TROUGH EXTENDS FROM 06N77W TO 06N100W THEN ITCZ TO 
BEYOND 07N140W. NO SIGNIFICANT CONVECTION IN THE ENTIRE AREA.

...DISCUSSION...
A COLD FRONT EXTENDING FROM NW CALIFORNIA TO AROUND 28N140W WILL 
MOVE SLOWLY SE...WEAKEN...AND DISSIPATE BY LATE FRIDAY. 
LARGE NW SWELL ASSOCIATED WITH THIS FRONT WILL SWEEP ACROSS THE 
WESTERN HALF OF THE DISCUSSION AREA THROUGH MONDAY...WITH 
COMBINED SEAS PEAKING AROUND 20 FT ALONG THE NORTHERN BOUNDARY W 
OF 130W FRIDAY AND SATURDAY. THE WAVE FORECAST IS A BLEND OF THE 
MORE AGGRESSIVE UKMET/NOGAPS WITH THE SHORTER WAVEHEIGHTS 
PREDICTED BY THE GFS/ECMWF.  

TRADEWINDS ACROSS THE AREA OF LARGE SWELL WILL BE GENERALLY NE 
AT 10-20 KT. HIGH PRESSURE WILL BUILD EASTWARD BEHIND THE FRONT 
ALONG 26N THROUGH MONDAY NIGHT. THE HIGH WILL BECOME THE 
DOMINANT SYNOPTIC FEATURE ACROSS THE REGION SATURDAY THROUGH 
TUESDAY... WITH LIGHT WINDS AND SEAS SUBSIDING FROM 15-17 FT TO 
ONLY 6-8 FT N OF 22N BY CHRISTMAS DAY. THE HIGH WILL ALSO 
ENHANCE E-NE TRADEWINDS S OF THE RIDGE AXIS AND N OF THE 
CONVERGENCE ZONE. EXPECT FRESH TO STRONG TRADEWINDS BETWEEN 09N 
AND 20N W OF 120W SUNDAY THROUGH TUESDAY. THE COMBINATION OF 
THESE ENHANCED TRADEWINDS WITH CONTINUED LONG-PERIOD NW SWELL 
SHOULD PRODUCE COMBINED SEAS OF AROUND 12 FT ON THESE DAYS SOUND 
OF 22N.  

GAP WINDS...
STRONG HIGH PRESSURE BEHIND A FAST-MOVING COLD FRONT MOVING 
SOUTHWARD IN THE WESTERN GULF OF MEXICO IS INDUCING A SUDDEN 
INCREASE IN GAP WINDS THROUGH CHIVELA PASS INTO THE GULF OF 
TEHUANTEPEC. THE SALINA CRUZ WEATHER STATION ALONG THE GULF OF 
TEHUANTEPEC COAST JUST REPORTED 30 KT N WINDS AT 03 UTC AFTER 
OBSERVING WEAK WINDS UP UNTIL THEN. AS SEEN IN SALINA 
CRUZ...WINDS ARE SUDDENLY AND DANGEROUSLY SURGING FROM NEAR CALM 
CONDITIONS AHEAD OF THE COLD FRONT TO GALE FORCE N WIND 
CONDITIONS WITHIN MINUTES. OVER THE GULF OF TEHAUNTEPEC...THESE 
WINDS WILL CONTINUE TO BUILD TO AROUND STORM FORCE BY FRIDAY 
MORNING. SEAS WILL RAPIDLY BUILD TO AROUND 22 FT IN BY LATE 
FRIDAY. GLOBAL MODEL GUIDANCE INDICATES WINDS AT OR NEAR STORM 
FORCE WILL BEGIN LATE TONIGHT AND CONTINUE THROUGH FRIDAY 
AFTERNOON...WITH GALE CONDITIONS THROUGH LATE SATURDAY NIGHT. 
WIND-DRIVEN SEAS WILL FAN OUTWARD FROM THE SOURCE REGION AS N-NE 
SWELL EXTENDING DOWNWIND FROM THE GULF OF TEHUANTEPEC TO 
110W...MERGING WITH NW SWELL FROM THE COLD FRONT MENTIONED 
EARLIER.

AS THE TRADEWIND FLOW INCREASES ACROSS THE SW CARIBBEAN BY 
FRIDAY... EXPECT NE TO E WINDS OF 20-25 KT AND SEAS BUILDING TO 
NEAR 12 FT IN AND DOWNSTREAM OF THE GULF OF PAPAGAYO BY SATURDAY 
AFTERNOON.

A 1940 UTC OCEANSAT SCATTEROMETER PASS STILL SUGGESTED NW 30 KT 
WINDS IN THE CENTRAL GULF OF CALIFORNIA.  THESE WINDS LIKELY 
HAVE DIMINISHED SLIGHTLY THIS EVENING.  FORCING FOR THESE WINDS 
WILL RELAX BY FRIDAY AFTERNOON.

$$
LANDSEA