000 AXPZ20 KNHC 040321 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC TUE SEP 04 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 0315 UTC. ...SPECIAL FEATURE... TROPICAL DEPRESSION JOHN IS AT 21.7N 114.6W 1003 MB AT 0300 UTC...MOVING NW OR 305 DEG AT 11 KT ALONG THE SW PERIPHERY OF A MID TO UPPER LEVEL RIDGE. CURRENTLY SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED WELL S OF THE CENTER FROM ROUGHLY 60 TO 420 NM OVER THE SW QUADRANT...AND WELL N OF THE CENTER FROM 60 NM TO 180 NM OVER NW QUADRANT. MAXIMUM SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT MAINLY OVER THE N SEMICIRCLE. JOHN IS EXPERIENCING NORTHEASTERLY WIND SHEAR AND IS ALSO BEGINNING TO MOVE OVER MUCH COOLER SURFACE WATERS...AND IS EXPECTED TO WEAKEN GRADUALLY WEAKEN OVER THE NEXT FEW DAYS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP5/WTPZ25 KNHC FOR MORE DETAILS. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS W TO E FROM THE PANAMA/COLOMBIA BORDER TO ACROSS PANAMA AND SOUTHERN COSTA RICA...TO THE PACIFIC AT 10N90W TO 10N106W WHERE IT LOSES IDENTITY IN THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH TROPICAL DEPRESSION JOHN. THE MONSOON TROUGH BECOMES DEFINED AGAIN SW OF TD JOHN NEAR 14N113W TO 08N132W WHERE LOW LEVEL INDICATES A TRANSITION TO AN ITCZ WHICH CONTINUES W TO BEYOND 09N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS OBSERVED WITHIN WITHIN 45 NM OF THE COAST FROM 81W TO 86W...WITHIN 120 NM EITHER SIDE OF A LINE FROM 05N83W TO 11N94W...WITHIN 60 NM EITHER SIDE OF A LINE FROM 09N95W TO 05N103W...AND WITHIN 90 NM OF LINE 06N110W TO 10N116W. ...DISCUSSION... A UPPER SHORTWAVE TROUGH EXTENDS SW INTO THE DISCUSSION AREA FROM 32N127W TO A BASE AT 20N132W. AN UPPER CYCLONE IS N OF THE AREA NEAR 37N138W WITH A SECOND SHORTWAVE TROUGH NOW MOVING OVER THE NW PORTION FROM 32N137W TO 28N136W. ALTHOUGH AN UPPER LEVEL ANTICYCLONE HAS CONTINUED TO SHIFT W AND FURTHER AWAY FROM THE DISCUSSION AREA TO NEAR 20N144W...IT STILL RIDGES E TO A SHARP CREST OVER THE DISCUSSION AREA AT 24N134W. THE NE PORTION OF THE DISCUSSION AREA CONTINUES TO DOMINATED BY AN LARGE UPPER RIDGE WITH EMBEDDED ANTICYCLONES CENTERED NEAR THE TEXAS/OKLAHOMA BORDER AT 34N96W...WITH A SECOND UPPER ANTICYCLONE OVER NORTHWESTERN OLD MEXICO NEAR 29N110W...WITH A MID/RIDGE EXTENDING SW TO A CREST OVER THE PACIFIC AT 26N127W. THE MID/UPPER ANTICYCLONIC FLOW ALONG THE SW PERIPHERY OF THIS EXTENSION OF THE LARGE RIDGE IS STEERING TD JOHN NW. JUST A LITTLE TO SW OF THE RIDGE CREST THE UPPER EASTERLY FLOW TURNS CYCLONICALLY S INTO AN UPPER TROUGH EXTENDING FROM 23N130W S INTO AN UPPER CYCLONE OVER THE DEEP TROPICS AT 11N131W. THE NORTHERN SEGMENT OF THIS UPPER TROUGH PASSES OVER THE REMNANT LOW PRESSURE 1010 MB OF TROPICAL CYCLONE ILEANA AT 21N127.5W. THIS REMNANT SURFACE LOW IS FORECAST TO CONTINUE TO MOVE SW REACHING NEAR 19N130W ON TUE AND WEAKEN INTO AN OPEN TROUGH ON WED. MAXIMUM WINDS HAVE DIMINISHED TO 20 KT WITHIN 420 NM OVER ITS NW QUADRANT TONIGHT EXPECTED TO SHRINK INWARD TO ABOUT 120 NM W OF THE TROUGH ON WED. THE UPPER LEVELS APPEAR VERY DRY OVER THE ENTIRE AREA W OF 124W. SCATTERED CONVECTION IS ENHANCED ALONG THE SE PERIPHERY OF THE UPPER RIDGE OVER INTERIOR MEXICO 22N TO 29N THEN RESUMES N OF TD JOHN NEAR 23N116W. THE DEBRIS MOISTURE FROM THIS CONVECTION IS SPREADING ANTICYCLONICALLY N...AND THEN NE AROUND THIS UPPER MEXICAN RIDGE...ROUGHLY COVERING THE BAJA CALIFORNIA PENINSULA S OF 30N...AND OVER ALL OF THE GULF OF CALIFORNIA...AND NOW SPREADING OVER THE EXTREME SOUTHERN PORTIONS OF ARIZONA AND NEW MEXICO. HOWEVER...THE DEBRIS MOISTURE FROM THE CONVECTION OVER THE S QUADRANT OF TD JOHN IS ADVECTED SW MERGING WITH ADDITIONAL MOISTURE OVER THE TROPICS S OF 22N BETWEEN 106W AND 116W. A BROAD INVERTED UPPER TROUGH IS NOTED OVER THE FAR SE PORTION OF THE DISCUSSION AREA FROM 19N98W TO JUST W OF THE GALAPAGOS ISLANDS. IMMEDIATELY TO THE E OF THIS UPPER TROUGH AN UPPER RIDGE EXTENDS W ACROSS THE W CARIBBEAN ALONG 14N TO A CREST OVER ISTHMUS OF TEHUANTEPEC AT 16N94W. THE ASSOCIATED WEAK UPPER DIFFLUENCE IS SUPPORTING THE CONVECTION ALONG THE E SEGMENT OF THE MONSOON TROUGH AS PREVIOUSLY MENTIONED. SOME OF THE DEBRIS MOISTURE IS NOW ADVECTED S ACROSS THE EQUATOR NEAR 101W...BUT MOST OF THE DEBRIS MOISTURE SPREADS NE ACROSS THE UPPER RIDGE OVER CENTRAL AMERICA TO THE E OF 95W...AND OVER THE W CARIBBEAN...BUT EVAPORATES BEFORE REACHING JAMAICA AND THE CAYMANS. ELSEWHERE AT THE LOW LEVELS...SURFACE HIGH PRESSURE IS CENTERED NW OF THE AREA RIDGES SE TO A CREST NEAR 27N121W. $$ NELSON