000
AXPZ20 KNHC 220950
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC MON DEC 22 2008

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

BASED ON 0300 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0900 UTC.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 07N77W 06N90W 07N105W 06N115W  
12N133W 09N140W. SCATTERED MODERATE CONVECTION IS FROM 10N TO 
13N BETWEEN 127W AND 133W.   

...DISCUSSION...
A REX BLOCK PATTERN IS WELL ESTABLISHED OVER MUCH OF THE 
DISCUSSION AREA...WITH A DEEP LAYERED CUT OFF LOW NEAR 
20.5N138.5W...WHICH WILL CONTINUE TO MOVE SLOWLY W AND GRADUALLY 
WEAKEN NEXT 48 HOURS. AN INVERTED SURFACE TROUGH CAN BE FOUND 
JUST A FEW DEGREES TO THE E OF THIS DEEP LAYERED LOW...EXTENDING 
FROM THE ITCZ ALONG 137W...NE TO 16N134W...AND MOVING W IN 
UNISON WITH ITS PARENT LOW. A BROAD ZONE OF LOW TO MID LEVEL 
CONVERGENCE AND ABUNDANT MOISTURE PERSISTS FROM THIS INVERTED 
LOW LEVEL TROUGH...N OF THE ITCZ AND E TO 116W. FAVORABLE UPPER 
LEVEL ANTICYCLONIC SHEAR AND UPPER DIVERGENCE IS VENTING 
SCATTERED TO NUMEROUS MODERATE CONVECTION...WITH ISOLATED STRONG 
CLUSTERS. THIS UNSTABLE REGIME WILL PERSIST THE NEXT 24 HOURS AS 
IT SLIDES GRADUALLY W. AT THE SURFACE...THE PRESSURE GRADIENT 
BETWEEN THE N PORTIONS OF THE INVERTED LOW LEVEL TROUGH AND A 
HIGH JUST TO THE NW IS MAINTAINING A BROAD BUT NARROWING ZONE OF 
20-25 KT NE TO E WINDS WITH SEAS OF 9-12 FT IN E WIND SWELL. 
THESE WINDS AND SEAS WILL SHIFT W AND NW AND SLOWLY DIMINISH 
DURING THE NEXT 48 HOURS.

THE UPSTREAM TROUGH IN THIS BLOCKING PATTERN WAS ALONG THE W 
COAST OF N AMERICA...AND WILL CONTINUE TO SHIFT E DURING THE 
NEXT 48 HOURS...WHILE A SHORT WAVE TROUGH WILL DIVE INTO THE W 
COAST BY 48 HOURS TO REESTABLISH THE UPPER TROUGH POSITION ALONG 
THE W COAST...AND SUPPORT ANOTHER COLD FRONT INTO N PORTIONS OF 
THE AREA. WINDS AROUND 20 KT WILL BE FOUND N OF THE FRONT...WITH 
SEAS BUILDING 10-14 FT N OF 28N BY 48 HOURS. 

THIS BLOCKING AND STAGNANT UPPER PATTERN IS EXPECTED TO HOLD FOR 
A FEW MORE DAYS BEFORE SLOWLY BREAKING DOWN AS A SERIES OF 
SHORTWAVES HELP DEEPEN THE TROUGH OVER THE NE PORTION OF THE 
AREA. 

GAP WINDS...
SEVERAL OF THE TYPICALLY WIND PRONE GAPS ARE ACTIVE TONIGHT... 
THOUGH NONE HAVE REACHED WARNING CRITERIA. STRONG HIGH PRESSURE 
BUILDING INTO THE CENTRAL U.S. BEHIND A GULF OF MEXICO COLD 
FRONT WILL INDUCE 20-25 KT FLOW THROUGH THE CENTRAL AMERICAN 
GAPS AND PASSES...EXTENDING DOWNSTREAM ACROSS TYPICAL ZONES. 
MEANWHILE HIGH PRESSURE RIDGING INTO THE N GULF OF CALIFORNIA 
BEHIND A FOLD FRONT HAS INDUCED A 20 KT NW TO N WIND FLOW 
THROUGH THE GULF...RAISING SEAS TO 6 FEET ACROSS THE S HALF OF 
THE GULF. AS THE NEXT FRONT APPROACHES THE BAJA OVER THE NEXT 
FEW DAYS...WINDS WILL BACK AHEAD OF THE FRONT AND REMAIN NEAR 20 
KT...WITH SEAS SUBSIDING TO LESS THAN 5 FEET. WINDS WILL SLACKEN 
BELOW 20 KT IN THE GULF OF TEHUANTEPEC BY 48 HOURS AS STRONG 
HIGH PRESSURE OPENS UP INTO THE GULF OF MEXICO...WHILE GAP 
FLOW THROUGH THE GULFS OF PAPAGAYO AND PANAMA REMAINS AT 20 KT 
AND GREATER. 

$$
STRIPLING