000 AXPZ20 KNHC 032151 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC MON SEP 03 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 2145 UTC. ...SPECIAL FEATURE... TROPICAL STORM JOHN IS AT 21.1N 114.0W 1002 MB AT 2100 UTC... MOVING NW OR 305 DEG AT 12 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 360 NM OVER THE SW QUADRANT...AND WELL N OF THE CENTER FROM 90 NM TO 240 NM OVER N QUADRANT. MAXIMUM SUSTAINED WINDS ARE 35 KT WITH GUSTS TO 45 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 TO A TROPICAL DEPRESSION TONIGHT...AND FURTHER WEAKEN TO REMNANT LOW IN 72 HOURS. 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 ALONG 08N FROM THE PANAMA/COLOMBIA BORDER TO ACROSS PANAMA AND SOUTHERN COSTA RICA...TO THE PACIFIC AT 10N88W...THEN DIPS SW TO 09N95W...THEN TURNS SLIGHTLY NW TO 11N105W WHERE IT LOSES IDENTITY IN THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH TROPICAL CYCLONE JOHN. THE MONSOON TROUGH BECOMES DEFINED AGAIN SW OF TROPICAL CYCLONE JOHN NEAR 16N112W...AND CONTINUES SW TO 07N132W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS OBSERVED WITHIN 150 NM EITHER SIDE OF A LINE FROM 05N79W TO 15N97W...AND ALSO WITHIN 75 NM OF 10.5N101W...AND WITHIN 60 NM EITHER SIDE OF A LINE FROM 06.5N TO 04.5N102.5W. SCATTERED MODERATE CONVECTION IS OBSERVED WITHIN 60 NM OF 07.5N111W. THUNDERSTORMS ALONG THE PACIFIC COAST OF W PANAMA AND COSTA RICA WILL MOVE W OFF THE COAST WITHIN THE NEXT FEW HOURS ACCOMPANIED BY FREQUENT LIGHTNING. ...DISCUSSION... A UPPER SHORTWAVE TROUGH EXTENDS SW INTO THE DISCUSSION AREA FROM 32N128W TO A BASE AT 20N132W. AN UPPER CYCLONE IS N OF THE AREA AT 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 23N135W. 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 34N97W...WITH A SECOND UPPER ANTICYCLONE OVER NORTHWESTERN OLD MEXICO NEAR 27N107W...WITH A MID/RIDGE EXTENDING SW TO A CREST OVER THE PACIFIC AT 25N127W. THE MID/UPPER ANTICYCLONIC FLOW ALONG THE SW PERIPHERY OF THIS EXTENSION OF THE LARGE RIDGE IS STEERING TROPICAL CYCLONE JOHN NW. JUST A LITTLE TO SW OF THE RIDGE CREST THE UPPER EASTERLY FLOW TURNS CYCLONICALLY S INTO AN UPPER TROUGH EXTENDING FROM 24N128W TO 18N131W INTO AN UPPER CYCLONE OVER THE DEEP TROPICS AT 11N131W. THE NORTHERN SEGMENT OF THIS UPPER TROUGH PASSES OVER THE REMNANT LOW PRESSURE 1009 MB OF TROPICAL CYCLONE ILEANA AT 21N127W. THIS REMNANT SURFACE LOW IS FORECAST TO CONTINUE TO MOVE SW REACHING NEAR 19N130W ON TUE...AND NEAR 17N133W ON WED WITH MAXIMUM WINDS OF 25 KT WITHIN 330 NM OVER ITS NW QUADRANT TODAY EXPECTED TO SHRINK INWARD TO ABOUT 150 NM BY MIDDAY WED. THE UPPER LEVELS APPEAR VERY DRY OVER THE ENTIRE AREA W OF 122W. ISOLATED CONVECTION IS ENHANCED ALONG THE SE PERIPHERY OF THE UPPER RIDGE OVER INTERIOR NW MEXICO FROM 28N103W TO 25N88W AND CONTINUING SW OVER THE PACIFIC JUST TO THE N OF TROPICAL CYCLONE JOHN AS PREVIOUSLY DESCRIBED. THE DEBRIS MOISTURE FROM THIS CONVECTION IS SPREADING ANTICYCLONICALLY N...AND THEN NE AROUND THIS UPPER MEXICAN RIDGE...ROUGHLY COVERING ALL OF THE BAJA CALIFORNIA PENINSULA...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 TROPICAL CYCLONE JOHN IS ADVECTED SW MERGING WITH ADDITIONAL MOISTURE OVER THE TROPICS S OF 22N BETWEEN 103W AND 114W. IF THE CONVECTION OVER INTERIOR MEXICO PERSISTS IT MAY MOVE W OVER THE EASTERN PORTION OF THE GULF OF CALIFORNIA TONIGHT...FROM 22N TO 25N. A BROAD INVERTED UPPER TROUGH IS NOTED OVER THE FAR SE PORTION OF THE DISCUSSION AREA FROM 17N99W TO OVER THE GALAPAGOS ISLANDS. IMMEDIATELY TO THE E OF THIS UPPER TROUGH AN UPPER RIDGE EXTENDS ACROSS W THE W CARIBBEAN ALONG 14N TO A CREST OVER WESTERN GUATEMALA. 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 100W...BUT MOST OF THE DEBRIS MOISTURE SPREADS NE ACROSS THE UPPER RIDGE OVER CENTRAL AMERICA TO THE E OF 93W...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