000 AXPZ20 KNHC 280243 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC FRI SEP 28 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0215 UTC. ...SPECIAL FEATURES... POST-TROPICAL CYCLONE MIRIAM NEAR 22.0N 116.7W 999 MB AT 0300 UTC SEP 28 MOVING S OR 180 DEG AT 1 KT. MAXIMUM SUSTAINED WINDS 30 KT GUSTS 40 KT. MIRIAM REMAINS A LOW LEVEL SWIRL OF CLOUDS... WITH SHALLOW CONVECTION OCCURRING ACROSS THE NE QUADRANT WITHIN 180 NM OF THE CENTER...AND HAS THUS LOST ITS TROPICAL CHARACTERISTICS. MIRIAM IS EMBEDDED WITHIN AN ELONGATED AND SOMEWHAT TRIANGULAR SHAPED CYCLONIC CIRCULATION OF THE LOWER TROPOSPHERE EXTENDING FROM OFFSHORE OF BAJA CALIFORNIA NORTE TO AROUND 10N. MIRIAM WILL GRADUALLY SPIN DOWN WITHIN THIS CIRCULATION DURING THE NEXT 72 HOURS AND IT DRIFTS W TO SW. SEAS SURROUNDING MIRIAM ARE EXPECTED TO FALL BELOW 12 FT WITHIN THE NEXT 12-18 HOURS. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS. A DEVELOPING LOW PRESSURE CENTER EMBEDDED WITHIN THE MONSOON TROUGH WAS NEAR 19N108W WITH AN ESTIMATED PRESSURE OF 1007 MB. IN FACT...SEVERAL LOW LEVEL SWIRLS ARE SUGGESTED BY SATELLITE IMAGERY ALONG THE MONSOON TROUGH ACROSS THIS GENERAL AREA...AS STRONG SW TO S WINDS CONTINUE TO GENERATE HORIZONTAL WIND SHEAR THAT IS AIDING IN THE FORMATION OF THE LOWS. THIS BROAD AREA OF WEATHER HAS TRACKED NW DURING THE PAST 24 HOURS AND HAS BECOME CAPTURED ON THE EASTERN FLANKS OF THE ELONGATED N TO S ALIGNED CYCLONIC CIRCULATION MENTIONED ABOVE WITH MIRIAM. STRONG S TO S-SE LOW LEVEL WIND FLOW IS EXPECTED TO TRANSPORT THIS EMBEDDED LOW CENTER N-NW TOWARDS THE S TIP OF BAJA CALIFORNIA AND THE SOUTHERN ENTRANCE INTO THE GULF OF CALIFORNIA DURING THE NEXT 24 HOURS. ASSOCIATED MAINLY SLY WINDS OF 20 TO 30 KT WITH GUSTS TO GALE FORCE WILL ACCOMPANY THIS LOW DURING THIS TIME...WITH ASSOCIATED SEAS 8 TO 12 FT. SATELLITE IMAGERY THIS EVENING SHOWS CONVECTION OCCURRING ALONG AND TO THE SE OF THE MONSOON TROUGH...EXTENDING FROM NEAR 11N130W SPIRALING NE THEN N TO THIS DEVELOPING LOW...WITH STRONG SLY FLOW CONTINUING NWD TO THE ENTRANCE INTO THE GULF OF CALIFORNIA. SCATTERED TO LOCALLY NUMEROUS MODERATE TO STRONG CONVECTION PREVAILS ALONG THIS ZONE OF STRONG MONSOON FLOW...AND WILL CONTINUE TO SPREAD NWD INTO S PORTIONS OF THE GULF OF CALIFORNIA...THE SOUTHERN BAJA PENINSULA...AND COASTAL MEXICO ADJACENT TO THE GULF. SQUALLS WITH WIND GUSTS IN EXCESS OF GALE FORCE CAN BE EXPECTED...AND WITH SCATTERED THUNDERSTORMS PRODUCING VERY HEAVY RAINFALL. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 36 HOURS BEFORE IT IS EXPECTED TO MOVE INLAND ACROSS MEXICO. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... MONSOON TROUGH FROM 11N79W TO LOW PRES NEAR 10N97W 1008 MB TO 12N100W WHERE IT FRACTURES...THEN RESUMES FROM LOW PRES NEAR 19N108W 1006 MB TO 16N107W TO 10N140W. SCATTERED MODERATE ISOLATED STRONG N OF 07.5N BETWEEN 80W AND 86W. SCATTERED MODERATE ISOLATED STRONG WITHIN 180 NM NW SEMICIRCLE OF LOW NEAR 10N97W. SCATTERED MODERATE TO STRONG S OF TROUGH TO 10N BETWEEN 106W AND 116W. SCATTERED MODERATE TO STRONG FROM 08.5N TO 11N BETWEEN 129W AND 133W. ...DISCUSSION... SUBTROPICAL HIGH CENTERED NEAR 33N142W 1022 MB EXTENDS A RIDGE SE AND ACROSS THE NW WATERS TO NEAR 29N119W. MODERATE TRADE WINDS ARE NOTED ON THE SOUTHERN PERIPHERY OF THE RIDGE AND W OF 140W BY RECENT SCATTEROMETER PASSES...WITH 7-9 FT SEAS IN MIXED NW SWELL AND NE WIND WAVES. LIGHT TO MODERATE W-SW WINDS ELSEWHERE E OF 105W ARE MAINTAINING A MOIST CONVECTIVELY UNSTABLE REGIME S OF THE TROUGH THAT IS EXPECTED TO REMAIN CONVECTIVELY ACTIVE THE NEXT FEW DAYS AS AN UPPER RIDGE REMAINS IN PLACE OVER THE MONSOON TROUGH AXIS. ACTIVE CONVECTION WILL CONTINUE NEAR AND TO THE W OF THE LOW NEAR 10N97W AND IS CONTINUES TO SHIFT W THROUGH FRI. TWO AREAS OF SWELL MOVING THROUGH THE REGION IN ADDITION TO SEAS GENERATED BY T.S. MIRIAM WILL CONTINUE TO AFFECT THE DISCUSSION AREA THROUGH TONIGHT. MODERATE LONG PERIOD SWELLS ARE SPREADING ACROSS THE WATERS NW OF MIRIAM. WHILE CROSS-EQUATORIAL SW SWELLS MOVING THROUGH SE PORTIONS ARE REACHING THE COAST OF MEXICO AND CENTRAL AMERICA...WITH ANOTHER STRONG PULSE TO FOLLOW TONIGHT... MERGING WITH 8-10 FT SEAS W OF 105W. ADDITIONAL PULSES OF NW SWELL WILL REACH THE NW CORNER OF THE DISCUSSION AREA FRI NIGHT AND SAT...BUILDING SEAS TO 9 FT. ROUGH SEAS...WITH SCATTERED TO NUMEROUS SQUALLS AND TSTMS WILL CONTINUE ACROSS FAR S PORTIONS OF THE GULF OF CALIFORNIA OVERNIGHT THROUGH FRI...AS MENTIONED ABOVE WITH THE DEVELOPING LOW PRESSURE CENTER. $$ STRIPLING