000 AXPZ20 KNHC 130251 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC TUE AUG 13 2013 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 0230 UTC. ...SPECIAL FEATURE... SATELLITE IMAGERY LATE THIS AFTERNOON AND EVENING SHOWED A COMPLEX CYCLONIC CIRCULATION ASSOCIATED WITH A TROPICAL LOW PRES SYSTEM...WITH A MEAN CENTER NEAR 13N129W AND ANALYZED AT 1008 MB. SEVERAL LOW LEVEL CYCLONIC SWIRLS COULD BE SEEN IN VISIBLE IMAGERY THROUGHOUT THE AFTERNOON ROTATING CYCLONICALLY ABOUT THE MEAN CENTER. SIGNIFICANT CONVECTION ASSOCIATED WITH THIS FEATURE CONTINUES TO OCCUR ACROSS THE SW QUADRANT OF THE LOW...WHERE THE BEST MOISTURE AND LLVL CONVERGENCE AREA OCCURRING. AS MENTIONED BELOW...AN INVERTED MID TO UPPER TROUGH APPROACHING THIS CIRCULATION THE PAST FEW DAYS FROM THE EAST HAS NOW MERGED WITH THIS LOWER LEVEL CIRCULATION. DRY AND STABLE CONDITIONS PERSIST ACROSS THE E SEMICIRCLE OF THE LOW OUT TO NEARLY 500 NM...AND IS LIMITING CONVECTION DEVELOPMENT BEYOND THE SOUTHWESTERN QUADRANT. THERE REMAINS AN OPPORTUNITY FOR THE LOW TO BECOME BETTER ORGANIZED OVER THE NEXT FEW DAYS...AND IT HAS A MEDIUM CHANCE OF INTENSIFYING INTO A TROPICAL CYCLONE OVER THE NEXT 48 HOURS AS IT TRACKS IN A GENERALLY WESTWARD MOTION. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... MONSOON TROUGH AXIS EXTENDS FROM CARIBBEAN LOW PRES NEAR 11.5N78W 1009 MB TO 11.5N87W TO WEAK LOW PRES NEAR 09N111.5W 1010 MB TO 10N114W WHERE IT REMAINS FRACTURED. TROUGH RESUMES NEAR 16N121.5W TO COMPLEX LOW PRES NEAR 13N129W 1008 MB TO 10N133W... WHERE IT TRANSITIONS TO ITCZ...CONTINUING TO BEYOND 12N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION NOTED FROM TROUGH S TO 07N E OF 87W. SCATTERED MODERATE CONVECTION NOTED WITHIN 180 NM S OF TROUGH BETWEEN 127W AND 132W. SCATTERED MODERATE TO STRONG CONVECTION NOTED WITHIN 90 NM N AND 60 NM S OF ITCZ W OF 135W. ...DISCUSSION... AN UPPER LEVEL ANTICYCLONE IS NOTED OVER FAR N CENTRAL MEXICO AT 30N106W WITH A RIDGE STRETCHING SW TO 20N137W...THROUGH A COL REGION...THEN CONTINUES SW TO ANOTHER ANTICYCLONE NEAR 15N145W. BROAD UPPER LEVEL SW TO W FLOW PREVAILS TO THE N AND NW OF THE RIDGE...WITH WATER VAPOR IMAGERY SHOWING MODERATE TO STRONG SUBSIDENCE ALLOWING FOR DRY AND STABLE ATMOSPHERIC CONDITIONS WITHIN AND NW OF THE RIDGE. E TO NE WINDS ALOFT GENERALLY PREVAIL ACROSS THE REMAINDER OF THE AREA S AND SE OF THE RIDGE...CONTINUING TO PRODUCE A GENERALLY LIGHTLY SHEARED ENVIRONMENT. THE TROPICAL LOW DESCRIBED ABOVE IN SPECIAL FEATURES IS OBSERVED TO THE S OF THE AFOREMENTIONED RIDGE. AN INVERTED MID TO UPPER TROUGH TO THE E OF THIS TROPICAL LOW HAS BEEN MOVING WWD THE PAST SEVERAL DAYS...GRADUALLY GETTING CLOSER TO THE LOW...AND APPEARS TO HAVE MERGED WITH THE BROAD CIRCULATION OF THIS LOW. UPPER CONVERGENCE BEHIND THIS FEATURE IS MAINTAINING STABLE CONDITIONS BETWEEN 124W AND 128W. THE UPPER ANTICYCLONE OVER N MEXICO IS AIDING IN PRODUCING A GENERAL NE TO E UPPER FLOW ACROSS PORTIONS OF THE AREA SE OF THE RIDGE AND E OF 120W. SATELLITE DERIVED WINDS INDICATED AN INVERTED MID LEVEL TROUGH OVER THE FAR EASTERN PART OF THE AREA TO THE S OF THE UPPER ANTICYCLONE...ROUGHLY FROM 25N115W TO 16N111W...DRIFTING WWD. INSTABILITY CREATED BY THIS FEATURE RESIDES OVER AN ABUNDANT POOL OF TROPICAL MOISTURE...AND A SURFACE TROUGH OFF THE S TIP OF BAJA CALIFORNIA...WHICH HAVE CONTINUED TO PRODUCE SCATTERED MODERATE CONVECTION THROUGHOUT THE DAY. HOWEVER...THIS CONVECTION HAS DIMINISHED DURING THE PAST FEW HOURS...BUT IS EXPECTED TO BECOME MORE ACTIVE S OF 23N TONIGHT AS THE SURFACE TROUGH DRIFTS VERY SLOWLY W. AT THE SURFACE...A WEAK 1021 MB HIGH IS ANALYZED NEAR 30N137W WITH A RIDGE EXTENDING SE TO NEAR 26N115W. THE WEAK PRES GRADIENT BETWEEN THE HIGH AND PERSISTENT LOW PRES ALONG THE SIERRA MADRES OCCIDENTALES HAS BEEN PRODUCING NNW WINDS 15-20 KT ALONG AND OFFSHORE OF THE W COAST OF BAJA CALIFORNIA TO ABOUT 120W...WHERE WAVE MODEL GUIDANCE AND A FEW SHIP OBSERVATIONS FROM THE PAST 24 HOURS INDICATED PEAK SEAS ARE 5-7 FT. THESE CONDITIONS ARE FORECAST TO GENERALLY PREVAIL OVER THE NEXT 24-48 HOURS...WITH BRIEF PULSING OF WINDS TO AROUND 20 KT WITH HIGHER GUSTS AND SEAS BRIEFLY 6-7 FT EXPECTED EACH OF THE NEXT FEW EVENINGS. THE HIGH IS FORECAST TO WEAKEN SLIGHTLY AS IT SHIFTS SLOWLY E DURING THE NEXT 24-48 HOURS. THE PRES GRADIENT BETWEEN THE HIGH AND THE MONSOON TROUGH CONTINUES TO SUPPORT NE WINDS OF 20-25 KT WITH SEAS PRESENTLY TO 9 FT TO THE NW AND N OF THE TROPICAL LOW NEAR 13N129W. THESE MARINE CONDITIONS ARE LIKELY TO PERSIST OVER THE NEXT 48 HOURS AS THE LOW BEGINS TO ACCELERATE TO THE W AT 15 TO 20 KT THE NEXT FEW DAYS. $$ STRIPLING