000 AXPZ20 KNHC 180954 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC THU DEC 18 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 IS CENTERED ALONG...05N77W TO 06N94W TO 07N106W TO 10N117W TO 07N127W TO 06N140W. SCATTERED MODERATE FROM 07N TO 11N BETWEEN 109W AND 122W. ...DISCUSSION... UPPER LEVEL PATTERN IS CHARACTERIZED AS AN OMEGA BLOCK OVER THE PACIFIC...WITH A HIGHLY AMPLIFIED UPPER RIDGE W OF 140W WITH A LONGWAVE UPPER TROUGH BETWEEN THE ROCKIES OF THE CONUS AND 140W. A SHARP UPPER LEVEL SHEAR AXIS TRAILS FROM THE BASE OF THE LONGWAVE TROUGH NEAR 22N125W TO 13N133W TO 11N134W. A SURFACE COLD FRONT ASSOCIATED WITH THE LONGWAVE TROUGH EXTENDS FROM A 1004 MB SURFACE LOW IN N ARIZONA TO THE BAJA OF CALIFORNIA NEAR 28N114W TO 19N133W. A QUIKSCAT PASS NEAR 18/0300 UTC DEPICTS WIDESPREAD NW TO N WINDS OF 25 TO 30 KT IN THE WAKE OF THE COLD FRONT. ADDITIONALLY...NORTHERLY SWELL CONTINUES TO ENTER THE FORECAST AREA FROM THE NORTH...WITH A SHIP OBSERVATION AND WAVE WATCH GUIDANCE SUGGESTING WAVE HEIGHTS TO 15 FT IN THIS SWELL. THIS SWELL WILL CONTINUE TO MOVE SOUTHWARD WITH MAXIMUM WAVE HEIGHTS DECREASING WITH TIME. DURING THE NEXT DAY...THE COLD FRONT WILL SLOWLY SAG SOUTHWARD BEFORE STALLING FROM THE SOUTH CENTRAL BAJA TO 17N122W AS THE CORRESPONDING UPPER SUPPORT REMAINS NEARLY STATIONARY. HOWEVER...A STRONG UPPER LEVEL JET STREAK IS FORECAST TO CREST THE AFOREMENTIONED UPPER RIDGE...FORCING THE BASE OF THE UPPER LONGWAVE TROUGH TO THE EAST TO RAPIDLY DIG SOUTHWARD. THIS...IN TURN...WILL SHED OFF AN UPPER LEVEL LOW BY 20/0600 UTC. THIS UPPER LOW IS FORECAST TO DEEPEN IN RESPONSE TO CONVECTIVE PROCESSES SUPPORTED BY AN ASSOCIATED UPPER LEVEL JET STREAK AND INSTABILITY UNDER THE PARENT UPPER TROUGH...RESULTING IN THE FORMATION OF A SURFACE TROUGH OVER THE E CENTRAL PACIFIC REGION. SOME GLOBAL MODELS INDICATE THAT A SURFACE LOW WILL DEVELOP ON THIS TROUGH. THIS WILL INCREASE THE SURFACE PRESSURE GRADIENT N OF THE TROUGH GIVEN THE PRESENCE OF A SURFACE RIDGE TO THE NORTH. AS SUCH...THE AREA OF 20+ KT WINDS OVER THE E CENTRAL PACIFIC WILL LIKELY EXPAND RAPIDLY IN THE 48- TO 72-HOUR TIME FRAME. THE EXACT LOCATION OF THIS REGION WILL BE HIGHLY MODULATED BY THE LOCATION OF THE INCIPIENT LOW AND TROUGH...AS WELL AS THE UPPER LOW. GLOBAL NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT WITH REGARD TO THIS SCENARIO...BUT DISAGREE SOMEWHAT IN THE STRENGTH OF THE INCIPIENT LOW AND CORRESPONDING SURFACE PRESSURE GRADIENT. NORTHEASTERLY TRADE WINDS OF 20 TO 25 KT CONTINUE ACROSS THE W CENTRAL PORTIONS OF THE AREA BASED ON A RECENT QUIKSCAT PASS. THIS AREA IS FORECAST TO MERGE WITH THE AREA OF 20-30 KT WINDS IN THE NEXT 48 HOURS IN RESPONSE TO THE AFOREMENTIONED TIGHTENING PRESSURE GRADIENT. ADDITIONALLY...NE WINDS OF 20 KT ARE FUNNELING INTO THE GULF OF PAPAGAYO AND GULF OF PANAMA BASED ON RECENT ASCAT PASSES. SIMILAR WINDS ARE EXPECTED TO CONTINUE OVER THE NEXT COUPLE DAYS. ADDITIONALLY...THE INCREASED PRESSURE GRADIENT RESULTING FROM SURFACE PRESSURE RISES OVER CENTRAL MEXICO IS BRINGING N WINDS OF 20 TO 25 KT TO THE GULF OF TEHUANTEPEC. OTHERWISE...WATER VAPOR IMAGERY DEPICTS A LARGE POOL OF UPPER LEVEL MOISTURE OVER THE E PACIFIC E OF 132W...MAINLY ACROSS E PORTIONS OF THE UPPER LONGWAVE TROUGH DISCUSSED ABOVE. TO THE W...DEEP LAYER DRY AIR IS WRAPPING AROUND THE TROUGH. FARTHER TO THE SOUTH...MAINLY ZONAL FLOW IS PRESENT OVER THE ITCZ AXIS... WITH A WEST-TO-EAST UPPER RIDGE S OF 19N E OF 112W PROVIDING AMPLE UPPER LEVEL DIVERGENCE FOR CONVECTION ASSOCIATED WITH THE ITCZ E OF 115W. ADDITIONALLY...LOW LEVEL CONVERGENCE ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM 13N117W TO 05N121W IS ENHANCING CONVECTION IN THE VICINITY OF THE ITCZ. $$ COHEN/CANGIALOSI