000
AXPZ20 KNHC 201559
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT DEC 20 2008

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1530 UTC.

...ITCZ...
05N77W TO 07N86W TO 05N95W TO 11N122W TO 11N121W TO 07N140W. 
SCATTERED MODERATE CONVECTION WITHIN 120 NM S OF AXIS BETWEEN 
109W AND 111W.

...DISCUSSION...

A LARGE MID- TO UPPER-LEVEL CLOSED CYCLONE CENTERED CLOSE TO 
21N132W HAS CARVED OUT A DEEP MID- TO UPPER-LEVEL TROUGH W OF 
115W. IN THE STRONGLY DIVERGENT REGION E OF THE TROUGH AXIS...
EARLIER QUIKSCAT DATA SUGGESTED THE FORMATION OF A WEAK 
LOW-LEVEL TROUGH STRETCHING FROM 10N TO 17N ALONG 121W AND 
MOVING W AT 10 KT. ALSO E OF THE TROUGH AXIS...THE FORCED ASCENT 
OF MOIST AND UNSTABLE AIR HAS LED TO THE FORMATION OF SCATTERED 
BANDS OF CONVECTION...SOME LOCALLY HEAVY. THE GRADIENT BETWEEN 
THE DEVELOPING LOW-LEVEL TROUGH AND ENHANCED LOW-LEVEL 
SUBTROPICAL RIDGING IS LEADING TO A BAND OF FRESH TO 
OCCASIONALLY STRONG TRADES EXTENDING ROUGHLY 300 NM EITHER SIDE 
OF A LINE FROM 23N118W TO 18N140W. QUIKSCAT AND ASCAT DATA 
INDICATE THAT ISOLATED NE WINDS OF UP TO 30 KT ARE OCCURRING 
OVER THE EASTERN PART OF THIS AREA...THOUGH MOST WINDS RANGE 
FROM 20 TO 25 KT. THE PERSISTENT NE WIND HAS LED TO STEEP NE 
WIND WAVES OF 8 TO 12 FT WITH PERIOD OF 6 TO 7 SEC...COMBINED 
WITH OLD NW SWELL COMING OUT OF THE NE PACIFIC.

OVER THE NEXT FEW DAYS...MODEL GUIDANCE SUGGESTS THAT THE CLOSED 
CYCLONE AND RELATED SURFACE LOW PRES WILL GRADUALLY TRACK W AS 
SUBTROPICAL RIDGING OVER THE NE PACIFIC SHIFTS W WITH IT. AS A 
RESULT...THE ZONE OF ENHANCED TRADES SHOULD OCCUPY A LARGE PART 
OF THE AREA FROM 15N TO 25N W OF 130W...WITH SEAS OF 8 TO 13 
FT...AGAIN IN STEEP NE WIND WAVES AND NW SWELL.

ELSEWHERE...ALTHOUGH THE LARGE-SCALE PATTERN IS GRADUALLY 
CHANGING...THE CONFIGURATION OF HIGH PRES OVER CENTRAL MEXICO 
AND RELATIVE LOW PRES TO THE S HAS KEPT N TO NE 20 TO 25 KT 
WINDS WITHIN THE IMMEDIATE COAST OF THE GULF OF TEHUANTEPEC WITH 
SEAS OF LESS THAN 8 FT. WINDS NEAR THE GULF OF TEHUANTEPEC 
SHOULD TAPER OFF LATER TODAY...ONLY TO RESTRENGTHEN WITH 
ADDITIONAL VIGOR BY MONDAY MORNING ONCE A NEW COLD FRONT PUSHES 
INTO THE GULF OF MEXICO.

QUIKSCAT AND ASCAT IMAGERY ALSO REVEAL NE WINDS OF 20 TO 25 KT 
DOWNWIND OF THE GULF OF PAPAGAYO...WITH SEAS LIKELY UP TO 8 FT. 
OVER THE LAST 24 HOURS...THESE WINDS APPEAR TO BE DIURNALLY 
DRIVEN WITH ACTIVE WINDS DURING THE DAYTIME HOURS AND WINDS LESS 
THAN 20 KT FROM DUSK TO ALMOST DAWN. MODEL GUIDANCE INDICATES 
THAT THIS TREND SHOULD CONTINUE OVER THE NEXT DAY OR TWO.

FINALLY...THE GRADIENT BETWEEN HIGH PRES BUILDING SOUTHWARD FROM 
THE WESTERN U.S. INTO NORTHERN MEXICO AND RELATIVE TO LOW PRES 
TO THE S IS RESULTING IN NW 20 TO OCCASIONALLY 25 KT WINDS IN 
THE GULF OF CALIFORNIA. WITH A LIMITED FETCH WIDTH...SEAS OF 4 
TO 7 FT ARE EXPECTED S OF 30N IN THE GULF OF CALIFORNIA DURING 
THE NEXT 48 HOURS. WINDS AND SEAS SHOULD BEGIN TO DIMINISH AND 
SUBSIDE THEREAFTER ONCE THE PRES EQUALIZES OVER THE REGION.


$$
KIMBERLAIN