000
AXPZ20 KNHC 281548
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN DEC 28 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 
1500 UTC.

...ITCZ...
THE INTERTROPICAL CONVERGENCE ZONE AXIS IS ALONG A LINE FROM 
08.5N83.5W TO 06N97W TO 09110W TO 08N126W TO 09N140W. NUMEROUS 
MODERATE AND ISOLATED STRONG CONVECTION TO CONTINUE WITH 120 NM 
OF 1008 MB LOW OFF COLUMBIA COAST NEAR 05.5N79.5W NEXT 24 HOURS 
AS LOW DRIFTS SW. ISOLATED MODERATE CONVECTION WITHIN 120 NM OF 
AXIS BETWEEN 88W AND 104W. SCATTERED MODERATE CONVECTION BETWEEN 
180 NM S AND 300 NM N OF AXIS BETWEEN 118W AND 140W.

...DISCUSSION...
THE TAIL OF A PROGRESSIVE SHORTWAVE TROUGH OVER THE MIDWEST 
EXTENDS WELL SOUTHWEST THROUGH NORTH CENTRAL MEXICO...ACROSS 
CENTRAL BAJA CALIFORNIA...AND THEN WESTWARD TO AROUND 23N123W. 
AS THE SHORTWAVE ABUTS AGAINST A LARGE AND DOMINANT RIDGE OF 
HIGH PRESSURE DOWNSTREAM...CENTERED OVER THE WESTERN ATLANTIC 
AND SOUTHEASTERN GULF OF MEXICO...LITTLE ADDITIONAL 
SOUTHEASTWARD PROGRESS OF THE TROUGH IS ANTICIPATED...AND THE 
SHORTWAVE SHOULD BEGIN TO LIFT OUT. A VERY BROAD AND FLAT 
TROPICAL UPPER RIDGE LIES ALONG 140W...WITH AN 85-100 KT JET 
SEGMENT RIDING OVER THE RIDGE BETWEEN 15N AND 20N...AND WAS 
CAPPING AND SHEARING CONVECTION OCCURRING WELL NORTH OF THE ITCZ 
IN THAT REGION...WHILE MAINTAINING MODERATE TO DEEP CONVECTION 
ALONG THE ITCZ. 

A COLD FRONT SUPPORTED BY THE MIDWEST SHORTWAVE TROUGH HAS 
PUSHED INTO THE NORTHERN HALF OF MEXICO AND PASSED THROUGH THE 
ENTIRE BAJA CALIFORNIA PENINSULA AND SHOULD SAG SOUTHWARD ALONG 
THE FRONT RANGE OF THE SIERRA MADRE ORIENTAL THIS AFTERNOON 
THROUGH TONIGHT...AND BARELY PUSH THROUGH THE ISTHMUS OF 
TEHUANTEPEC MONDAY MORNING. BRISK NW TO N WINDS OF 20 TO 30 KT 
PREVAIL BEHIND THE FRONT THROUGHOUT THE ENTIRE GULF OF 
CALIFORNIA...WITH SEAS LIKELY UP TO 8 FT S OF 29N...WHERE GAP 
FLOW BETWEEN INTERIOR ISLANDS CONTINUES TO FORCE WINDS TO 30 
KT...AT LEAST. AS WINDS BEGIN TO GRADUALLY DIMINISH LATER 
TONIGHT AND MON IN THE GULF OF CALIFORNIA...A FRESH SURGE OF 
HIGH PRESSURE BEHIND THE STALLING FRONT IN THE WESTERN GULF OF 
MEXICO SHOULD CAUSE WINDS TO RAPIDLY INCREASE ACROSS AND 
DOWNWIND OF THE GULF OF TEHUANTEPEC BY MON MORNING. MODELS NOW 
SUGGESTING A GALE EVENT FOR 24 TO 30 HOURS...INTO TUE. DUE TO 
THE LENGTH OF FETCH...SEAS SHOULD BRIEFLY BUILD UP TO 9 OR 10 FT 
DOWNWIND OF THE GULF OF TEHUANTEPEC EARLY TUE BEFORE SUBSIDING 
ON WED.

WELL BEHIND THE COLD FRONT...THE SHORTWAVE HAS DEPOSITED A 1031 
MB SURFACE HIGH NEAR 32N130W WHICH HAD BEEN SLIDING SLOWLY EAST 
OVER THE PAST 24 HOURS...BUT APPEARS TO HAVE RECENTLY BECOME 
STATIONARY. A STRONG PRESSURE GRADIENT SOUTH OF THIS RIDGE OF 
THE EASTERN PACIFIC WATERS HAS LED TO MODERATE TO STRONG TRADES 
OVER A LARGE EXPANSE FROM 10N TO 26N AND W OF 118W. LONG PERIOD 
NW TO N SWELL PROPAGATING STRAIGHT OUT OF THE NORTH CENTRAL AND 
NE PACIFIC HAS BEEN FLOODING THE NW HALF OF THE FORECAST AREA 
AND HAS COMBINED WITH NE WIND WAVES AND/OR SWELL AS A RESULT OF 
THE PERSISTENT...ENHANCED TRADES. THIS HAS PRODUCED CONFUSED 
SEAS OF 10 TO 17 FT OVER THE ABOVE MENTIONED AREA. THE LEADING 
EDGE OF THE NORTHERLY WAVETRAIN CONTINUES TO PROPAGATE SOUTHWARD 
AND IS CROSSING INTO THE SOUTHERN HEMISPHERE. OVER THE NEXT FEW 
DAYS...THE NW TO N SWELL SHOULD FADE RATHER QUICKLY...WHILE THE 
ZONE OF ENHANCED TRADES DIMINISHES SIGNIFICANTLY IN AREAL EXTENT.

FINALLY...AN ENHANCED LOW-LEVEL RIDGE OVER THE WESTERN ATLANTIC 
EXTENDS WEST SW INTO THE E GULF OF MEXICO AND NW CARIBBEAN SEA 
AND HAS ACTED TO ENHANCE THE TRADE WIND FLOW ACROSS THE ENTIRE 
CARIBBEAN AND ACROSS CENTRAL AMERICA DURING THE LAST FEW DAYS.  
WINDS ACROSS COSTA RICA AND PANAMA HAD BEEN MORE N TO NE 
YESTERDAY AND HAVE AIDED IN SPINNING UP THE 1008 MB LOW OFF OF 
THE COLUMBIAN COAST. HOWEVER...DURING THE PAST 12 HOURS THIS LOW 
HAS DETACHED FROM THE ITCZ...AND A MORE NE TO E FLOW HAS RESUMED 
BLOWING STRONGLY ACROSS CENTRAL AMERICA E OF 90W...AND THE GAP 
WINDS ACROSS THE GULF OF PAPAGAYO HAVE BROADENED AND INCREASED 
OVERNIGHT AND THIS MORNING. RENEWED WAVE GROWTH DOWNWIND OF 
PAPAGAYO WILL INCREASE SEAS 8 TO 9 FT TONIGHT THROUGH MONDAY 
MORNING. A GRADUAL DECREASE IN THIS WIND FLOW IS EXPECTED BY 24 
TO 36 HOURS. THEREAFTER...AS SURFACE RIDGING EXPANDS SOUTHWARD 
BEHIND THE FRONT OVER MEXICO...A RESURGENCE OF GAP WIND 
CONDITIONS DOWNWIND OF THE GULF OF PAPAGAYO IS LIKELY FOR WED 
AND THU.

$$
STRIPLING