000 AXPZ20 KNHC 010355 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SAT SEP 01 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 FEATURES... TROPICAL STORM ILEANA CENTERED AT 22.6N 116.7W AT 01/0300 UTC. ILEANA IS MOVING NW OR 300 DEG AT 07 KT WITH AN ESTIMATED MINIMUM CENTRAL PRESSURE OF 991 MB. MAXIMUM SUSTAINED WIND SPEED IS 55 KT WITH GUSTS TO 65 KT. SCATTERED MODERATE ISOLATED STRONG CONVECTION REMAINS CONCENTRIC WITHIN ABOUT 90 NM OF CENTER. THE CYCLONE IS MOVING OVER INCREASINGLY COOLER SEAS SURFACE WATERS AND MORE STABLE ATMOSPHERIC CONDITIONS AND IS EXPECTED TO STEADILY WEAKEN. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP4/WTPZ24 KNHC FOR MORE DETAILS. TROPICAL LOW...AN ILL-DEFINED CYCLONIC SWIRL IS NOTED WITHIN THE MONSOON TROUGH NEAR 12N101W. SCATTERED MODERATE ISOLATED STRONG DISORGANIZED CONVECTION IS NOTED WITHIN 60 NM OVER W SEMICIRCLE OF CENTER. GLOBAL GUIDANCE SUGGESTS THAT THIS LOW PRESSURE WILL MOVE W TONIGHT THEN TURN NW AND DEEPEN WITH POSSIBLE TROPICAL CYCLONE DEVELOPMENT. THE GRADIENT BETWEEN STRONG HIGH PRESSURE BRIDGING SW ACROSS THE GULF OF MEXICO AND THROUGH THE ISTHMUS OF TEHUANTEPEC AND LOW PRESSURE WITHIN THE BROAD MONSOON TROUGH HAS ENHANCED EASTERLY WINDS TO 20 TO 25 KT WELL TO THE NE AROUND 420 NM FROM THE ESTIMATED CENTER. THE LOW IS FORECAST TO BE NEAR 14N104W LATE SAT AND NEAR 16N108W LATE SUN. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS W FROM THE AT THE PANAMA/COLOMBIAN BORDER ACROSS SW PANAMA TURNING NW ALONG THE PACIFIC COAST OF COSTA RICA...THEN MOVING OFFSHORE PARALLELING THE PACIFIC COAST OF NICARAGUA...EL SALVADOR AND NICARAGUA TO 13N91W WHERE IT TURNS ABRUPTLY SW INTO AN EMBEDDED LOW PRESSURE NEAR 12N101W. THE MONSOON TROUGH RESUMES AT 14N118W AND EXTENDS SW TO 10N130W THEN W TO BEYOND 11N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED WITHIN 120 NM OF COAST OF CENTRAL AMERICA FROM 82W TO 100W AND ALSO ELSEWHERE FROM 06N TO 17N BETWEEN 93W AND 110W. SCATTERED MODERATE CONVECTION IS NOTED WITHIN 30 NM EITHER SIDE OF A LINE FROM 17N111W TO 11N116W AND ANOTHER LINE FROM 10N129W TO 08N134W. ...DISCUSSION... A LONG WAVE UPPER TROUGH DOMINATES THE EASTERN N PACIFIC WITH AN EMBEDDED SHORTWAVE SWINGING SE AND BECOMING NEGATIVE TILT OVER THE DISCUSSION AREA FROM 32N123W TO 27N120W. A SECOND SHORTWAVE IS NOW REINFORCING FROM 32N130W TO 24N128W. AS THE INITIAL SHORTWAVE LIFTS FURTHER NE THE WEAKENING TROPICAL CYCLONE ILEANA SHOULD TURN MORE WESTERLY AS THE STEERING RIDGE WILL THEN BUILD FURTHER W. AN UPPER LEVEL ANTICYCLONE IS CENTERED AT 22N132W WITH ITS ENVELOPE OF ANTICYCLONIC UPPER FLOW COVERING THE AREA FROM 11N TO 22N BETWEEN 127W AND 146W. THESE FEATURES COMBINE TO DRY OUT THE UPPER LEVELS TO THE W OF A LINE EXTENDING FROM CALIFORNIA/ARIZONA BORDER AT 32N114W TO 13N140W WITH THIS UPPER STABILITY CONTRIBUTING THE WEAKENING TREND OF TROPICAL CYCLONE ILEANA. THE UPPER ANTICYCLONE OVER TROPICAL CYCLONE ILEANA HAS NEARLY DISSIPATED WITHIN THE MORE PREDOMINATE UPPER RIDGE EXTENDING SW FROM A LARGE ANTICYCLONE OVER NORTHWESTERN OLD MEXICO AT 29N108W. SOME OF THE DEBRIS MOISTURE FROM ILEANA CONCENTRATES INTO A 360 NM WIDE PLUME EXTENDING SW TO NEAR 12N130W WHERE IT EVAPORATES. SOME OF THE TROPICAL CYCLONE DEBRIS MOISTURE ALSO CONCENTRATES INTO A 240 NM WIDE THAT SPREADS NE AROUND THE W PERIPHERY OF THE UPPER ANTICYCLONE ACROSS THE NORTHERN BAJA CALIFORNIA PENINSULA...THE NORTHERN GULF OF CALIFORNIA...EXTREME NW OLD MEXICO AND IS NOW SPREADING OVER SE ARIZONA AND SW NEW MEXICO. AN UPPER TROUGH ORIGINATING IN THE CENTRAL N ATLANTIC CONTINUES SW ACROSS THE NW CARIBBEAN AND ACROSS THE YUCATAN PENINSULA TO OVER THE TROPICAL E PACIFIC AT 14N94W...THEN TURNS SE THROUGH 05N97W CROSSING THE EQUATOR JUST E OF THE GALAPAGOS ISLANDS. AN UPPER RIDGE IS BUILDING W ACROSS THE EASTERN PORTION OF CENTRAL AMERICA. AN AREA OF UPPER DIFFLUENCE IS INDUCED OVER CENTRAL AMERICA...AND OVER THE EASTERN PORTIONS OF THE PACIFIC MONSOON TROUGH...AND IS SUPPORTING INTENSE CONVECTION OVER AND JUST OFFSHORE NICARAGUA AND GUATEMALA. THE RESULTANT DENSE UPPER DEBRIS MOISTURE IS ADVECTED S ACROSS THE EQUATOR BETWEEN 78W AND 103W. ELSEWHERE AT THE LOW LEVELS...SOUTHWESTERLY MONSOONAL FLOW AT 15 TO 20 KT WINDS WITH SEAS 8 TO 11 FT ARE OBSERVED FROM 03N TO 22N FROM 122W TO THE COAST OF MEXICO...MERGING WITH THE SW AND W WIND WAVE OVER THE S SEMICIRCLE OF TROPICAL CYCLONE ILEANA. LONG PERIOD CROSS EQUATORIAL SOUTHWESTERLY SWELL AT 15 TO 19 SECONDS HAS REACHED ALONG 07N BETWEEN 78W AND 86W RESULTING IN SEAS TO 9 FT...WITH THIS AREA OF SW SWELLS EXPECTED TO SUBSIDE OVER THE NEXT 48 HOURS. MIXED SOUTHERLY LONG PERIOD SWELL AT 14 TO 18 SECONDS IS NOTED FROM 03N TO 17N BETWEEN 88W AND 122W AND IS ALSO EXPECTED TO SUBSIDE OVER THE NEXT COUPLE OF DAYS. $$ NELSON