000 AXPZ20 KNHC 262223 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC WED SEP 26 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... TROPICAL STORM MIRIAM WAS CENTERED NEAR 20.8N 115.4W 994 MB AT 2100 UTC SEP 26 MOVING N OR 350 DEG AT 6 KT. MAXIMUM SUSTAINED WINDS 50 KT GUSTS 60 KT. ESTIMATED MINIMUM CENTRAL PRESSURE WAS 994 MB. CONVECTION NEAR MIRIAM CONTINUES TO BE DISRUPTED BY VERTICAL WIND SHEAR AND INGESTION OF VERY DRY MID LEVEL AIR. THIS IS ALLOWING FOR ONLY SCATTERED MODERATE CONVECTION WITHIN 120 NM SE QUADRANT AND SCATTERED MODERATE CONVECTION ELSEWHERE FROM 90 TO 210 NM ACROSS THE E SEMICIRCLE OF CENTER. SLOW AND GRADUAL WEAKENING IS EXPECTED FOR MIRIAM AND IT MOVES N-NW TONIGHT THEN MORE NW THU AND FRI. COOLER WATERS...CONTINUED VERTICAL WIND SHEAR...AND DRY AIR ENTERING THE SYSTEM ON THE W SIDE ARE EXPECTED TO BRING ABOUT THIS GRADUAL DEMISE. SWELLS GENERATED BY MIRIAM WILL CONTINUE TO AFFECT THE PACIFIC COASTS OF SOUTH AND SOUTH CENTRAL BAJA PENINSULA DURING THE NEXT COUPLE OF DAYS. THESE SWELLS WILL PRODUCE STRONG SURF AND LEAD TO VERY DANGEROUS AND LIFE-THREATENING RIP CURRENT CONDITIONS ACROSS EXPOSED COASTLINES. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS. A DEVELOPING TROPICAL LOW PRESSURE CENTER WAS ESTIMATED NEAR 13N105W AT 1009 MB...AND EMBEDDED WITHIN A LARGE LOWER TROPOSPHERIC CYCLONIC CIRCULATION...ROUGHLY BETWEEN 100W AND 110W. THE SURFACE LOW HAS DEVELOPED ALONG THE MONSOON TROUGH...AND ABUNDANT TROPICAL MOISTURE HAS CONVERGED WITHIN AND AROUND THE PERIPHERY OF THIS CIRCULATION. SCATTERED TO NUMEROUS MODERATE TO STRONG CONVECTION DESCRIBED ABOVE IS OCCURRING ASSOCIATED WITH THIS FEATURE...AND WILL CONTINUE WITHIN THE BROAD CIRCULATION AS THE FEATURE IS IN A FAVORABLE ENVIRONMENT...A HIGH PRES RIDGE ALOFT...FOR SUSTAINED CONVECTION. VISIBLE SATELLITE IMAGERY THIS AFTERNOON SHOWED A LARGE LOW LEVEL WIND SURGE OF 20-25 KT MOVING FROM THE DEEP TROPICS INTO THE EASTERN SEMICIRCLE OF THIS SYSTEM...AND LIKELY BUILDING SEAS TO 8 TO 10 FT THERE. THIS SYSTEM IS EXPECTED TO CONTINUE TO SHIFT NW AROUND 10 KT THE NEXT FEW DAYS...AND HAS A MODERATE CHANCE OF DEVELOPING INTO A TROPICAL CYCLONE DURING THAT TIME. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... MONSOON TROUGH EXTENDS FROM 10N75W TO LOW PRES NEAR 09N89W 1010 MB TO LOW PRES NEAR 13N105W 1009 MB TO 13.5N110W WHERE IT FRACTURES...THEN RESUMES FROM S OF MIRIAM NEAR 13N116W TO 10N138W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON TO BEYOND 11N140W. SCATTERED MODERATE ISOLATED STRONG WITHIN 240 NM S OF TROUGH BETWEEN 86W AND 96W. SCATTERED TO LOCALLY NUMEROUS MODERATE TO STRONG FROM 08.5N TO 18.5N BETWEEN 100W AND 110W. ...DISCUSSION... UPPER LEVEL RIDGING EXTENDING E TO W BETWEEN 10N AND 22N HAS BEEN DISSECTED BY A DIGGING MIDDLE TO UPPER LEVEL TROUGH JUST TO THE W OF MIRIAM. THE TROUGH WAS NEARLY N TO S ALONG 119W...AND HAS BECOME INVOLVED WITH MIRIAM...INDUCING 20-25 KT OF VERTICAL SWLY WIND SHEAR...AND INTRODUCING DY AND SUBSIDENT AIR INTO W PORTIONS OF THE BROADER CIRCULATION OF MIRIAM. THE TROUGH WILL DRIFT E THROUGH THU AND THEN WEAKEN CONSIDERABLY. TO THE W AND E OF THIS TROUGH RESIDE UPPER RIDGES...CENTERED ON UPPER ANTICYCLONES NEAR 18N138W AND 16N101W. THIS GENERAL RIDGE ALIGNMENT IS EXPECTED TO REMAIN IN PLACE THROUGH FRI. A 1025 HIGH CENTERED NEAR 34N141W AND EXTENDS A RIDGE SE AND ACROSS N PORTIONS TO NEAR 28N118W. A SHRINKING AREA OF FRESH TRADE WINDS ON THE SOUTHERN PERIPHERY OF THE RIDGE WAS IDENTIFIED BY RECENT SCATTEROMETER PASSES FROM 12.5N TO 15N W OF 132W...WHERE SEAS ARE RUNNING 8-10 FT IN MIXED NW SWELL AND BUILDING NE WIND WAVES. THE AERIAL EXTENT OF THE FRESH TRADES WILL CONTINUE TO DECREASE DURING THE NEXT 24 HOURS AS HIGH PRES WEAKENS. ELSEWHERE E OF 110W...LIGHT TO MODERATE MONSOONAL FLOW IS MAINTAINING A MOIST AND UNSTABLE REGIME S OF THE TROUGH...AND WILL REMAIN ACTIVE CONVECTIVELY DURING THE NEXT FEW DAYS AS THE UPPER RIDGE REMAINS IN PLACE. TWO SWELL EVENTS PLUS SEAS GENERATED BY T.S MIRIAM ARE IMPACTING THE REGIONAL WATERS. MODERATE TO LARGE LONG PERIOD SWELLS FROM THE NW ARE SPREADING ACROSS THE NW WATERS...RAISING SEAS TO 7-9 FT TO THE W AND NW OF MIRIAM. MEANWHILE...A NEW PULSE OF CROSS EQUATORIAL SW SWELLS HAS MOVED THROUGH SE PORTIONS AND REACHED THE COAST OF MEXICO AND CENTRAL AMERICA WITH ANOTHER STRONG PULSE TO FOLLOW TONIGHT THROUGH THU. THESE SWELLS ARE ALREADY MERGING WITH SEAS OF 8 TO 11 FT AFFECTING MOST OF THE FORECAST WATERS W OF 105W. SWELLS GENERATED BY HURRICANE MIRIAM WILL CONTINUE TO REACH THE COASTS OF MEXICO TO PRODUCE STRONG AND LARGE SURF AND DANGEROUS RIP CURRENTS WITHIN THE SURF ZONE FROM THE SOUTH HALF OF BAJA CALIFORNIA TO NEAR MANZANILLO. SMALL SOUTHERLY SWELL FROM MIRIAM HAS MOVED THROUGH THE ENTRANCE INTO THE GULF OF CALIFORNIA AND WILL CREATE SMALL BUT STRONG SURF ALONG EXPOSED COASTLINES S OF 27N THROUGH THU MORNING. $$ STRIPLING