000
AXPZ20 KNHC 160932
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE DEC 16 2008

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

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0900 UTC.

...ITCZ...
INTERTROPICAL CONVERGENCE ZONE...05N77W TO 08N105W TO 09N125W TO 
06N140W. SCATTERED MODERATE CONVECTION WITHIN 120 NM EITHER SIDE 
OF THE AXIS BETWEEN 77W AND 81W AND BETWEEN 97W AND 130W.

...DISCUSSION...
SPLIT UPPER FLOW REGIME RESIDES OVER THE E PACIFIC REGION...WITH 
A PRIMARY POSITIVELY-TILTED LONGWAVE TROUGH N OF 31N E OF 
138W...WITH A SECONDARY AND MORE COMPACT UPPER TROUGH TO THE S 
AND AN ASSOCIATED UPPER LOW NEAR 22N129W. THE LONGWAVE TROUGH IS 
ASSOCIATED WITH A SURFACE COLD FRONT THAT EXTENDS FROM 32N112W 
TO 31N129W. N OF THIS COLD FRONT...PERSISTENT N TO NW GRADIENT 
WINDS ARE OCCURRING...WITH SPEEDS OF 20 TO 25 KT PER RECENT 
QUIKSCAT PASSES AND SHIP REPORTS. THESE INCREASED WINDS ARE 
GENERATING NW TO N SWELL...WHICH IS EXPECTED TO EXPAND ACROSS A 
LARGE PART OF THE FORECAST AREA OVER THE NEXT 48 HOURS. SEAS OF 
8 TO 12 FEET WILL BE FOUND IN THIS SWELL...WITH THE HIGHEST SEAS 
OVER N PORTIONS OF THE FORECAST AREA. DURING THE NEXT 24 
HOURS...THE AFOREMENTIONED SECONDARY UPPER TROUGH AND UPPER LOW 
ARE FORECAST TO BECOME ABSORBED BY THE LONGWAVE TROUGH IN 
RESPONSE TO THE APPROACH OF A 110-KT UPPER LEVEL JET STREAK 
EMBEDDED WITHIN THE LONGWAVE TROUGH RESULTING IN THE LONGWAVE 
TROUGH DIGGING SOUTHWARD. AS SYNOPTIC-SCALE ASCENT INCREASES 
DOWNSTREAM OF THE LONGWAVE TROUGH AXIS AND INTERACTS WITH 
AMBIENT VERTICAL VORTICITY ASSOCIATED WITH THE PRE-EXISTING 
SURFACE COLD FRONT W OF THE BAJA...THE INDUCED STRONG SURFACE 
PRESSURE FALLS ARE FORECAST TO SPIN UP A SURFACE LOW THAT WILL 
QUICKLY BE EJECTED INTO THE PLAINS OF THE CONUS LATE THIS WEEK. 
THE TIGHTENING SURFACE PRESSURE GRADIENT AROUND THIS LOW WILL 
LIKELY GENERATE ANOTHER AREA OF 20-25 KT WESTERLY WINDS TO THE W 
OF THE FRONT NEAR THE INCIPIENT SURFACE LOW. AFTER THE LOW 
DEVELOPS...THE N TO NW WINDS BEHIND THE COLD FRONT WILL 
POTENTIALLY AID IN THE EXPANSION OF THE 8+ FOOT SEAS AREA. 
CONFIDENCE IN THIS SOLUTION IS RATHER HIGH GIVEN STRONG 
CONSISTENCY AMONG GLOBAL MODELS.

ELSEWHERE ACROSS THE FORECAST AREA...TRADE WINDS CONTINUE TO 
DOMINATE SOUTHERN PORTIONS OF THE REGION AT THE SOUTHERN 
PERIPHERY OF A SURFACE RIDGE ORIGINATING FROM A 1026 MB SURFACE 
HIGH NEAR 32N143W. NE WINDS OF 20 TO 25 KT ARE OCCURRING AS THE 
TRADES FUNNEL INTO THE GULF OF PAPAGAYO. A SHIP RECENTLY 
TRAVELING NORTHWESTWARD RECENTLY ENCOUNTERED WINDS NEAR 25 KT... 
CONSISTENT WITH A RECENT QUIKSCAT PASS DEPICTING NE WINDS OF 20 
TO 25 KT IN A NARROW SWATH NEAR AND DOWNWIND OF THE GULF OF 
PAPAGAYO. THE PERSISTENT TRADES WILL LIKELY CONTINUE TO RESULT 
IN THESE GAP WINDS DURING THE NEXT COUPLE DAYS. THESE TRADE 
WINDS ARE ALSO REACHING SPEEDS OF 20 TO 25 KT WITH SEAS OF 8 TO 
10 FT OVER WEST CENTRAL PORTIONS OF THE REGION. WHILE WIND 
SPEEDS IN THIS AREA ARE FORECAST TO DIMINISH SOMEWHAT DURING THE 
NEXT COUPLE DAYS IN RESPONSE TO SURFACE PRESSURE FALLS TO THE 
NORTH...THE AFOREMENTIONED HIGHER SWELLS WILL LIKELY OVERTAKE 
THIS AREA.

OTHERWISE...WATER VAPOR IMAGERY DEPICTS A LARGE POOL OF UPPER 
LEVEL MOISTURE OVER THE E PACIFIC E OF 126W...MAINLY ACROSS E 
PORTIONS OF THE TWO UPPER TROUGHS PREVIOUSLY DISCUSSED. TO THE 
W...DEEP LAYER DRY AIR IS BEGINNING TO WRAP AROUND THE COMPACT 
SECONDARY TROUGH...WHILE A LONGWAVE UPPER RIDGE IS BRINGING 
SUBSIDENCE IN NORTHWESTERLY FLOW ALOFT W OF 137W. TO THE 
SOUTH...MAINLY ZONAL FLOW IS PRESENT OVER THE ITCZ AXIS...WITH A 
WEST-TO-EAST UPPER RIDGE S OF 16N E OF 105W PROVIDING AMPLE 
UPPER LEVEL DIVERGENCE FOR CONVECTION ASSOCIATED WITH THE ITCZ 
E OF 105W.

$$
COHEN/CANGIALOSI