000 AXPZ20 KNHC 201004 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC WED MAY 20 2009 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... AXIS WAS ALONG 09N79W TO 07N87W TO 09N99W TO 09N108W TO 11N115W TO 1009 MB LOW 11N120W TO 05N132W TO 05N140W. SCATTERED TO NUMEROUS MODERATE WITH ISOLATED STRONG CONVECTION WAS WITHIN 180 NM OF AXIS BETWEEN 114W AND 96W. SCATTERED MODERATE CONVECTION WAS WITHIN 180 NM S OF LOW AND WITHIN 120 NM N OF AXIS FROM 120W TO 136W. ISOLATED MODERATE CONVECTION WAS NOTED ELSEWHERE NEAR THE AXIS. .DISCUSSION... SHARP MID/UPPER TROUGH EXTENDS FROM CENTRAL CALIFORNIA SSW TO A CYCLONIC VORTEX AT 30N124W...WITH ASSOCIATED BROAD MID LEVEL CYCLONIC FLOW DOMINATING MUCH OF THE AREA N OF 20N AND FROM 135W TO BAJA CALIFORNIA. ALONG THE W COAST OF THE BAJA...A NEGATIVE TILT UPPER TROUGH EXTENDS FROM THE VORTEX ABOVE TO OFFSHORE OF MAINLAND MEXICO NEAR 20N...WITH A SHARP DOWNSTREAM RIDGE COMBINING WITH THIS TROUGH TO ENHANCE DIURNAL CONVECTION ALONG THE SIERRA MADRE OCCIDENTALES. UPPER LEVEL RIDGING EXTENDED W TO E ALONG ABOUT 10-11N...FROM 145W TO 85W. DRY SUBSIDENT AIR CONTINUES TO DOMINATE MOST OF THE AREA W OF 120W DUE TO THIS BROAD PERSISTENT TROUGH...WHILE ABUNDANT MOISTURE REMAINS TRAPPED TO THE E AND SE...COVERING MOST OF THE TROPICAL EPAC E OF 120W...AND EXTENDING N INTO THE EXTREME SRN GULF OF CALIFORNIA. AN UPPER LEVEL S/W COULD BE SEEN IN WATER VAPOR IMAGERY MOVING E INTO S CENTRAL MEXICO...AND HELPING TO ROTATE THE UPPER TROUGH ALONG THE MEXICAN COAST MORE NEGATIVELY TILTED WITH TIME. THIS UPPER TROUGHING RESIDING ACROSS THE AREA FOR THE PAST SEVERAL DAYS IS FORECAST TO BEGIN TO LIFT E AND THEN NE OVER THE NEXT 24-36 HOURS AND BRIEFLY LEAVE A ZONAL...WLY...FLOW ALOFT THERE...BEFORE ANOTHER S/W MOVES E INTO THE AREA AND REDEVELOPS THE TROUGHING IN NEARLY THE SAME LOCATION ALONG 120W MON AND TUE. WINDS ALOFT W OF TROUGH REMAIN QUASI-ZONAL WITH DUE W JET CORE OF 75-85 KT. A WELL DEFINED 1008 MB LOW WAS ALONG THE ITCZ AT 11N120W WITH TROUGHING EXTENDING NNE AND SSW. THIS LOW HAS BECOME STATIONARY AND MAY BEGIN TO DRIFT TO THE E AND NE NEXT 24 HOURS...AND GRADUALLY WEAKEN. CHANCES FOR TROPICAL DEVELOPMENT ARE CONSIDERED LOW. FURTHER TO THE E...ALONG THE ITCZ BETWEEN 102W AND 105W...A LARGE CLUSTER OF DEEP CONVECTION HAS DEVELOPED TONIGHT...WITH LOW TO MID LEVEL CYCLONIC TURNING NOTED IN IR SATELLITE IMAGERY. WLY WIND SHEAR ALOFT IS LIGHT AND HAS DIMINISHED IN THE PAST 24 HOURS. SHARP TROUGHING AT THE SURFACE HAS RECENTLY BEEN SUGGESTED BY SCATTEROMETER PASSES. THIS BROAD CIRCULATION IS FORECAST BY GLOBAL MODELS TO MOVE SLOWLY W INTO THE WEAKEN AND GRADUALLY BECOME BETTER ORGANIZED...BEFORE BEGINNING TO LIFT NE AND E LATE SUN INTO EARLY NEXT WEEK. THERE IS SOME POTENTIAL FOR TROPICAL DEVELOPMENT OF THIS SYSTEM IN THIS TIME FRAME. ELSEWHERE AT THE SURFACE... PREVIOUS HIGH PRES NEAR 28N126W HAS DISSIPATED AS COLD FRONT APPROACHES NORTHERN FRINGES OF FORECAST WATERS. FRONT EXPECTED TO MOVE E INTO CALIFORNIA WITH NEW HIGH PRES 1032 MB MOVING W INTO AREA JUST N OF E PAC. GRADIENT BETWEEN HIGH PRES AND LOW PRES 1003 MB OVER ARIZONA CAUSING GALE FORCE WINDS ALONG CENTRAL CALIFORNIA COASTAL WATERS AND BUILDING MODERATE N-NW SWELL SPREADING S JUST N OF 25N E OF 117W BY THU. GAP WINDS...AN EVENING QUIKSCAT PASS SHOWED GALE FORCE WINDS AGAIN IN THE GULF OF TEHUANTEPEC...AND WILL LIKELY PERSIST OVERNIGHT DUE TO A COMBINATION OF NOCTURNAL DOWNSLOPE FLOW...AND MOMENTUM TRANSFER FROM A OLD WEAKENED MID LEVEL DISTURBANCE DIVING S INTO THE BAY OF CAMPECHE...WITH COLDER AIR BEHIND IT. GALE FORCE WINDS SHOULD DIMINISH WITHIN A FEW HOURS AFTER SUNRISE...AND THEN REMAIN CLOSE TO 25-30 KT THROUGH THE AFTERNOON AND THEN DIMINISH RATHER QUICKLY THROUGH THU. SEAS DOWNWIND OF TEHUANTEPEC TO 102W RUNNING 8 TO 11 FT AND WILL SLOWLY SUBSIDE BY 36 HOURS. $$ STRIPLING