000 AXPZ20 KNHC 252214 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC TUE SEP 25 2012 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2115 UTC. ...SPECIAL FEATURES... HURRICANE MIRIAM CENTERED NEAR 18.9N 114.9W 979 MB AT 2100 UTC SEP 25 MOVING WNW OR 300 DEG AT 4 KT. MAXIMUM SUSTAINED WINDS 75 KT GUSTS 90 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 979 MB. NUMEROUS STRONG CONVECTION WAS NOTED FROM 17N TO 21N BETWEEN 112.5W AND 115.5W...WHILE SCATTERED MODERATE TO STRONG CONVECTION WAS ELSEWHERE WITHIN 150 NM NE SEMICIRCLE. THIS CONVECTION HAS DECREASED CONSIDERABLY IN THE PAST 6-8 HOURS AS MIRIAM HAS BEGUN TO ENCOUNTER SWLY UPPER LEVEL WIND SHEAR. AS MIRIAM BEGINS TO TURN MORE N-NW THIS EVENING AND CONTINUE ON THAT COURSE THROUGH EARLY THU...SLOW AND GRADUAL WEAKENING IS FORECAST. LONG PERIOD SWELL GENERATED BY MIRIAM WILL CONTINUE TO AFFECT THE SOUTH AND WEST COASTS OF THE SOUTHERN BAJA PENINSULA DURING THE NEXT COUPLE OF DAYS...AND THE W COAST OF MEXICO FROM ACAPULCO INTO THE SOUTHERN GULF OF CALIFORNIA. THESE SWELLS ARE LIKELY TO CAUSE STRONG AND POWERFUL SURF LEADING TO DANGEROUS AND POTENTIALLY LIFE THREATENING RIP CURRENT CONDITIONS. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... MONSOON TROUGH EXTENDS FROM COLOMBIA NEAR 10N75W TO 09N87W TO 12N97W TO LOW PRES NEAR 11N102.5W 1009 MB WHERE IT FRACTURES... THEN RESUMES FROM S OF MIRIAM NEAR 14N115W TO 12N129W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON TO BEYOND 10N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION S OF TROUGH TO 05.5N E OF 90W. SCATTERED MODERATE TO STRONG CONVECTION FROM 07N TO 15N BETWEEN 95W AND 110W. ...DISCUSSION... UPPER LEVEL RIDGING EXTENDS NEARLY E TO W ALONG 16-18N AND FROM 07N TO 26N...BETWEEN OLD MEXICO AND 144W...WITH TWO DISTINCT ANTICYCLONIC CIRCULATIONS ON EACH END OF RIDGE. PROGRESSIVE WLY UPPER LEVEL FLOW GENERALLY PREVAILS N OF THE RIDGE...WITH A MIDDLE TO UPPER LEVEL S/W SINKING E-SE IN BETWEEN THE TWO ANTICYCLONES ALONG 121W. A MIDDLE LEVEL CYCLONE WITHIN THE S/W IS NOTED IN WATER VAPOR IMAGERY NEAR 25N121W...AND HAS BEGUN TO PRODUCE MODEST BUT DEEP LAYERED SWLY WIND SHEAR UPON MIRIAM...AS MENTIONED ABOVE. S OF 15N AND E OF 110W...NELY WINDS TO 45 KT PREVAIL ACROSS THE SE QUADRANT OF THE UPPER RIDGE...AND ARE PROVIDING A FAVORABLE ENVIRONMENT FOR CONTINUED DEEP CONVECTION ALONG AND NEAR THE MONSOON TROUGH THERE. OTHERWISE STRONG SUBSIDENCE WITH DRY AND STABLE AT THE MIDDLE AND UPPER LEVELS IS ACROSS THE AREA N OF 16N W OF 120W. A 1025 HIGH CENTERED NEAR 36N140W EXTENDS A RIDGE ACROSS NW PORTIONS TO NEAR 25N124W. AN AREA OF 20 KT TRADE WINDS ON THE SOUTHERN PERIPHERY OF THE RIDGE WAS IDENTIFIED BY AFTERNOON SCATTEROMETER PASSES FROM 13N TO 17N BETWEEN 128W AND 138W...WHERE SEAS ARE RUNNING 8-10 FT IN MIXED NW SWELL AND BUILDING WIND WAVES. THE AERIAL EXTENT OF THE FRESH TRADES WILL DECREASE DURING THE NEXT 24 HOURS AS HIGH PRES MOVES WWD AND WEAKENS. A PERTURBATION OR WAVE HAS DEVELOPED ALONG THE MONSOON TROUGH IN THE VICINITY OF 102W...WHERE A 1009 MB SURFACE LOW IS FOUND ALONG THE TROUGH ABUNDANT TROPICAL MOISTURE IS CONVERGING AROUND A BROAD LOW LEVEL CYCLONIC CIRCULATION THERE BETWEEN 97W AND 110W...AND WILL REMAIN ACTIVE CONVECTIVELY FOR THE NEXT 24-36 HOURS. TWO SWELL EVENTS PLUS SEAS GENERATED BY HURRICANE MIRIAM ARE IMPACTING THE REGIONAL WATERS. LARGE AND LONG PERIOD SWELLS FROM THE NW ARE SPREADING ACROSS THE NW WATERS RAISING SEAS TO AROUND 9 FT MAINLY W OF A LINE FROM 30N120W TO 12N130W TO 05N140W. CROSS EQUATORIAL SW SWELLS ARE REACHING THE COAST OF MEXICO PARTICULARLY E OF 105W. THESE SWELL EVENTS WILL MERGE THIS EVENING AND TONIGHT WITH SEAS OF 8 TO 11 FT AFFECTING MOST OF THE FORECAST WATERS W OF 105W...EXCEPT HIGHER SEAS ASSOCIATED WITH HURRICANE MIRIAM. $$ STRIPLING