000
AXPZ20 KNHC 261005
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED DEC 26 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 ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM 06N78W TO 09N85W TO 07N92W WHERE 
LOW LEVEL WINDS SUGGEST IT TRANSITIONS TO THE ITCZ AND CONTINUES
TO 06N104W TO 09N116W TO 08N132W TO 06N140W. SCATTERED MODERATE
CONVECTION IS WITHIN 120 NM N OF THE ITCZ BETWEEN 119W-125W AND
ALSO WITHIN 60 NM N OF THE ITCZ BETWEEN 125W-127W.

...DISCUSSION...

A DEEP UPPER LEVEL TROUGH JUST APPROACHING THE WESTERN U.S. WITH
GENERALLY A ZONAL FLOW PATTERN TO ITS S COVERS THE MUCH OF THE 
DISCUSSION AREA TO NEAR 25N. ABUNDANT UPPER LEVEL MOISTURE IN 
THE FORM OF MOSTLY BROKEN HIGH CLOUDS IS STREAMING EWD IN THE 
THIS FLOW PATTERN ACROSS THE AREA FROM 25N TO 32N. THIS MOISTURE 
SPREADS EWD TO ACROSS NORTHERN BAJA CALIFORNIA AND E TO THE SW
U.S. A SURFACE COLD FRONT ASSOCIATED WITH THE UPPER TROUGH EXTENDS
FROM CENTRAL CALIFORNIA SW TO 32N126W AND WEAKENS TO NEAR 
29N136W. AN ASCAT PASS FROM 0522 UTC THIS MORNING REVEALED A VERY
PRONOUNCED NW WIND FLOW BEHIND THE FRONT JUST N OF 32N AND BETWEEN
THE FRONT AND 136W.

A SHARPENING UPPER TROUGH AHEAD OF A LARGELY AMPLIFIED RIDGE WELL
W OF THE DISCUSSION AREA IS FAST APPROACHING THE NW CORNER OF 
THE AREA. THE TROUGH IS TAPPING TROPICAL CENTRAL PACIFIC 
MOISTURE THAT IS BEING CONTRIBUTED TO THAT ALREADY IN PLACE 
ACROSS THE NORTHERN SECTION OF THE AREA AS MENTIONED ABOVE. THIS
TROUGH WILL MOVE THROUGH THE WRN AND CENTRAL PORTIONS OF THE 
AREA N OF ABOUT 18N THROUGH THU...AND TO THE FAR NE PORTION FRI
WHERE IT BEGINS TO PHASE OUT AS BROAD TROUGHING BUILDS SWD. THE
AFOREMENTIONED COLD FRONT WILL WEAKEN AS IT QUICKLY SHIFTS E OF 
THE AREA TO THE SW U.S. BY EARLY TONIGHT. A HIGH PRES CENTER OF
1028 MB WELL NW OF THE AREA EXTENDS A RIDGE SEWD TO 32N135W AND
TO NEAR 26N117W. THE PRES GRADIENT BETWEEN THE HIGH CENTER AND
RELATIVELY LOWER PRES IN THE TROPICAL REGION OF THE AREA IS 
RESULTING IN FRESH TO STRONG TRADES FROM 08N TO 16N BETWEEN 121W
AND 130W...AND ALSO FROM 07N TO 19N W OF 130W WHERE SEAS ARE 
10 TO 12 FT IN MIXED NW AND NE SWELLS. ELSEWHERE SW OF A LINE 
FROM ABOUT 21N140W TO 24N115W TO 00N100W WINDS ARE 20 KT OR LESS
...WITH SEAS TO 9 FT PRIMARILY IN A NW SWELL.

THE HIGH IS FORECAST TO MOVE SE TO NEAR 36N135W OVER THE NEXT
24 HRS WHILE SLIGHTLY WEAKENING. THE TRADES WILL RESPOND BY 
SHRINKING A LITTLE IN AREAL COVERAGE FROM THE E. THE HIGH WILL 
CONTINUE TO MOVE SE THROUGH LATE THU AND CONTINUE TO WEAKEN. 
THIS WILL ALLOW FOR A WEAK COLD FRONT TO APPROACH THE FAR NW 
CORNER OF THE AREA. MODELS INDICATE THAT THIS FRONT WILL PASS 
JUST TO THE N OF 32N THROUGH FRI AS ANOTHER HIGH PRES AREA IN 
ITS WAKE BUILDS SE INTO THE AREA. THE TRADES FROM 10N TO 20N 
THEN EXPAND SOME IN AREAL COVERAGE FRI. ALTHOUGH THE COLD FRONT 
BYPASSES THE AREA JUST TO THE N...A BATCH OF LARGE NW SWELLS 
WITH SEAS MAXING OUT TO 11 OR 12 FT BEHIND THE FRONT WILL 
PROPAGATE SEWD TO JUST MAKE IT INTO THE EXTREME FAR NRN REACHES 
OF THE AREA BY LATE FRI.

TO THE S OF 25N...BROAD ANTICYCLONIC FLOW IS PRESENT BETWEEN 100W
AND AN UPPER TROUGH THAT EXTENDS FROM 22N125W SW TO 10N136W TO 
NEAR 01N132W. BROKEN TO OVERCAST MOSTLY MID AND HIGH LEVEL CLOUDS 
ARE STREAMING EWD TO THE E OF THE TROUGH TO 110W WHERE THEY 
TEND TO THIN OUT IN A DRIER ATMOSPHERIC ENVIRONMENT...WITH ONLY
A NARROW PLUME...ABOUT 190 NM IN DIAMETER...EXTENDS E TO ACROSS
CENTRAL MEXICO.

GULF OF TEHUANTEPEC...A COLD FRONT WILL PUSH THROUGH THE GULF OF 
MEXICO...DELIVERING A SURGE OF COLDER AND DRIER AIR DOWN THE 
COAST OF MEXICO TOWARD THE ISTHMUS OF TEHUANTEPEC BEGINNING AND
INTO THE GULF OF TEHUANTEPEC BEGINNING EARLY THIS EVENING AND
INTO EARLY THU. A GALE WARNING HAS BEEN ISSUED FOR THE GULF OF 
TEHUANTEPEC WED EVENING AND LASTING THOUGH TONIGHT BEFORE
WINDS DIMINISH TO BELOW GALE FORCE BY THU MORNING. 

$$
AGUIRRE