000 AXPZ20 KNHC 171603 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC WED DEC 17 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... INTERTROPICAL CONVERGENCE ZONE...04N76W TO 06N86W TO 06N100W TO 09N108W TO 09N130W TO 07N140W. SCATTERED MODERATE CONVECTION FROM 08N TO 13N BETWEEN 106W AND 112W ASSOCIATED WITH WEAK LOW LEVEL CYCLONIC CURL WILL PERSIST ACROSS THIS AREA NEXT 12 HOURS. SCATTERED MODERATE CONVECTION FROM 06N TO 10N BETWEEN 115W AND 120W WILL PERSIST NEXT 12 HOURS. SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 180 NM OF THE AXIS BETWEEN 125W AND 140W...AND WILL BECOME MORE CONCENTRATED E OF 132W NEXT 12 HOURS. ...DISCUSSION... LONGWAVE UPPER TROUGH WAS ALONG THE CONUS W COAST THIS MORNING... WITH AN EMBEDDED STRONG UPPER LOW CONTINUING TO DIG S AND E INTO THE CENTRAL CALIFORNIA COAST...BUT HAS SLOWED ITS EASTWARD PROGRESS DURING THE PAST 6 HOURS. A SECONDARY MID TO UPPER TROUGH LINGERING MANY DAYS FURTHER TO THE SOUTH HAS BECOME ABSORBED...AND EXTENDED SW TO 10N137W. COLD AIR CONTINUES TO DIVE INTO BACK SIDE OF ENTIRE LONGWAVE TROUGH...AND WILL AID IN MAINTAINING STRONG BAROCLINICITY AND GRADUAL EASTWARD PROGRESS OF THE TROUGH N OF 30N. STRONG LIFT/UPWARD MOTION EAST AND EXTENDING DOWNSTREAM OF THE TROUGH AXIS...IS BEING MAINTAINED BY AN 80 TO 120 KT JET STREAMING NE ACROSS THE BAJA...NRN MEXICO...AND INTO THE SW U.S. THE INTERACTION OF THIS STRONG LIFT WITH A FRONTAL ZONE EXTENDING W OF THE S CALIFORNIA/BAJA BORDER HAS INDUCED A DEEPENING LOW CENTER ALONG THE COAST JUST SOUTH OF THE BORDER... WITH A 1008 MB SURFACE LOW ANALYZED AT 17/1200 UTC NEAR 32N117W. BRISK N WINDS OF 20-30 KT TO THE N AND W OF THIS LOW HAS PUSHED AN ATTENDANT SURFACE COLD FRONT FROM THE LOW TO 25N124W TO 23N132W...WITH SEAS 10 TO 16 FT IN LARGE N SWELL BEHIND THE FRONT AND E OF 140W. GALE FORCE SW TO S WINDS ARE SUGGESTED TO BE OCCURRING ALONG AND WITHIN 180 NM E OF THIS FRONT AND PARENT LOW...EXTENDING ACROSS THE EXTREME N PORTIONS OF THE GULF OF CALIFORNIA....WHERE STEEPENING WAVES TO 6 FEET ARE EXPECTED DURING THE NEXT 6 HOURS. THIS LOW IS FORECAST TO MOVE SLOWLY E INTO NORTHERN BAJA/EXTREME SOUTHERN CALIFORNIA DURING THE NEXT 18 HOURS BEFORE IT IS EJECTED OVER THE WESTERN CONUS. HIGH SEAS IN THIS LARGE N SWELL GENERATED BEHIND THE FRONT WILL PROPAGATE SOUTH AND SOUTHEASTWARD...WITH WAVEWATCH GUIDANCE INDICATING SEAS OF 10 TO 14 FEET SPREADING 35N TO 22N BY 24 HOURS AND THEN SLOWLY DIMINISHING 10 TO 12 FEET 24 TO 48 HOURS. N WIND FLOW BEHIND THE EJECTED SURFACE LOW WILL FORCE THE FRONTAL ZONE FARTHER SE AND ACROSS ALL BUT THE SOUTHERN THIRD OF THE BAJA...AND FORCE THE FRONT SOUTHWARD INTO THE SUBTROPICAL EASTERN PACIFIC. HOWEVER...THESE WINDS WILL LIKELY TO DECREASE WITH THE RELAXING SURFACE PRESSURE GRADIENT FROM THE DEPARTURE OF THE SURFACE LOW. NORTHEASTERLY TRADE WINDS OF 20 TO 25 KT CONTINUE ACROSS A LARGE PART OF THE AREA NW AND W OF THIS THE COLD FRONT...BASED ON RECENT QUIKSCAT PASSES...WITH INCREASING WAVE HEIGHTS 8 TO 10 FT RESULTING FROM PERSISTENT NE WIND FLOW AND BUILDING NORTHERLY SWELL. THE AREA OF 20+ KT WINDS IS EXPECTED TO SHRINK OVER THE NEXT COUPLE DAYS IN RESPONSE TO THE APPROACH OF THE FRONTS FROM THE NW. ADDITIONALLY...N TO NE GAP WINDS 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. MARINE CONDITIONS ACROSS THE EQUATORIAL EASTERN PACIFIC W OF 85W WILL REMAIN SEASONABLE DURING THE NEXT 24 HOURS...WITH MODERATE S TO SE TRADE WINDS...AND A MIXTURE OF MODEST WIND WAVES AND MERGING LONG PERIOD SWELL ENERGY FROM BOTH HEMISPHERES. E OF 85W WINDS WILL REMAIN DOMINATED BY 15 TO 25 KT ONSHORE FLOW ASSOCIATED WITH AN ACTIVE COLUMBIAN LOW. WATER VAPOR IMAGERY AND CIMSS TPW PRODUCTS DEPICT LARGE POOLS OF MOISTURE OVER THE TROPICAL E PACIFIC E OF 140W...WITH WEAK EASTERLY WAVES SUGGESTED ALONG 131W...117W...AND 110W. ANTICYCLONIC SHEAR ASSOCIATED WITH THE AMPLIFIED UPPER TROUGH DISCUSSED ABOVE WILL CONTINUE TO PRODUCE VERY FAVORABLE VENTILATION AND UPPER DIVERGENCE DURING THE NEXT 12 TO 24 HOURS FOR ACTIVE ITCZ CONVECTION EAST OF THE UPPER TROUGH AXIS...AND MOST CONCENTRATED NEAR THESE WEAK EASTERLY PERTURBATIONS. $$ STRIPLING