000 AXPZ20 KNHC 180348 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC THU DEC 18 2008 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0330 UTC. ...ITCZ... INTERTROPICAL CONVERGENCE ZONE IS CENTERED ALONG...4N77W 6N90W 6N100W 10N112W 9N125W 6N132W 6N140W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 110W -112W. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 112W-120W. ...DISCUSSION... LONGWAVE UPPER TROUGH EXTENDS FROM THE FAR NW REGION OF THE CONUS SW THROUGH TO CENTRAL CALIFORNIA WHERE AN UPPER LEVEL LOW MOVING NE IS LOCATED NEAR 35N119W. THE FRONT THEN CONTINUES SW INTO THE AREA SW THROUGH 32N123W TO 25N128W TO 20N133W AND FURTHER SW AS A NARROW TROUGH TO NEAR 10N136W. THE UPPER FLOW BEHIND THE TROUGH IS DEPICTED AS CONFLUENT ON WATER VAPOR IMAGERY. THIS ALLOWING FOR A COLD AIR MASS TO FUNNEL INTO THE BACK SIDE OF THE LONGWAVE TROUGH. THIS WILL MAINTAIN STRONG BAROCLINICITY WITH THE TROUGH MOVING EWD AT ABOUT 20 KT N OF 23N. THE ASSOCIATED SURFACE COLD FRONT EXTENDS FROM A 1005 MB LOW OVER NORTHERN BAJA CALIFORNIA SW TO 26N117W TO 21N123W. IT IS MOVING E 20-25 KT. THE LOW IS FORECAST TO QUICKLY LIFT NE ACROSS THE WESTERN CONUS THROUGH THU MORNING AS THE UPPER LEVEL LOW OVER CENTRAL CALIFORNIA BECOMES ABSORBED BY THE NORTHERN PORTION OF THE LONGWAVE TROUGH OVER THE NW U.S. AND THE MAIN AREA OF FAVORABLE UPWARD LIFT EJECTS NE TO WELL NE OF THE NE PART OF THE AREA. NW WINDS OF 20-25 KT ARE OCCURRING TO THE NW OF THE FRONT...BUT ARE FORECAST TO DIMINISH OVER THE NEXT 48 HRS AS THE FRONT DISSIPATES OVER THE FAR E PART OF THE AREA OVER THE SUB-TROPICAL PACIFIC NEAR SOUTHERN BAJA CALIFORNIA AS ITS MAIN UPPER LEVEL SUPPORT LIFTS NE OF THE MARINE AREA. ANTICYCLONIC SHEAR ASSOCIATED WITH THE AMPLIFIED UPPER TROUGH DISCUSSED IN FIRST PARAGRAPH WILL CONTINUE TO PRODUCE VERY FAVORABLE VENTILATION AND UPPER DIVERGENCE DURING THE NEXT 12-24 HRS FOR ACTIVE ITCZ CONVECTION EAST OF THE UPPER TROUGH AXIS...AND MOST CONCENTRATED NEAR WEAK LOW LEVEL TROUGHS MOVING THROUGH THE ITCZ FROM E TO W WITH THE MOST NOTICEABLE ONE ALONG 114W. THE MAIN MARINE PROBLEM CONTINUES TO BE THE RELATIVELY HIGH SEAS IN N SWELLS BEHIND THE FRONT THROUGH AT LEAST THU EVENING. SEAS UP TO 15 FT ARE INITIALLY BEING OBSERVED NEAR 28N127W...BUT ARE FORECAST BY WAVEWATCH MODEL GUIDANCE TO SUBSIDE TO 12 FT BY THU AFTERNOON AND TO 9 FT OVER THE AREA FROM 20N-25N E OF 121W BY FRI AFTERNOON. NE TRADE WINDS OF 20-25 KT THROUGH THE GULF OF PAPAGAYO WILL CHANGE LITTLE OVER THE NEXT 48 HOURS AS PRES GRADIENT OVER CENTRAL MEXICO ADJUSTS VERY LITTLE. GULF OF PANAMA N WINDS TO 20 KT WILL DIMINISH TO LESS THAN 20 KT IN 18 HRS. SIMILAR WINDS IN THE GULF OF TEHUANTEPEC WILL DIMINISH TO LESS THAN 20 KT IN 48 HRS. NE TRADES WILL CONTINUE OVER AN AREA THAT OVERLAPS THAT DESCRIBED BEHIND THE FRONT FROM 10N TO 25N W OF 125W. SEAS HERE ARE IN THE RANGE OF 8-10 FT. THIS AREA OF NE TRADES IS EXPECTED TO GREATLY DIMINISH OVER THE NEXT COUPLE DAYS AS HIGH PRES RIDGING OVER THE WESTERN PORTION OF THE AREA BREAKS DOWN AS THE NEXT FRONTAL SYSTEM ENCROACHES INTO THE NW CORNER IN ABOUT 18 HRS WEAKENS AT 48 HRS. NO SIGNIFICANT WINDS ARE EXPECTED WITH THIS NEXT FRONT. GAP WINDS... N TO NE WINDS OF 20 TO 25 KT ARE FUNNELING INTO AND DOWNSTREAM OF THE GULFS OF PANAMA...PAPAGAYO AND TEHUANTEPEC AREAS...AND WILL GENERATE BUILDING SEAS TO 6 FEET JUST OFFSHORE...INCREASING 6 TO 8 FEET FURTHER DOWNSTREAM. $$ AGUIRRE