000 AXPZ20 KNHC 292157 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC WED AUG 29 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 ILEANA IS CENTERED NEAR 18.5N 113.0W AT 29/2100 UTC. ILEANA IS MOVING NW OR 320 DEG AT 07 KT AROUND THE W PERIPHERY OF AN UPPER RIDGE THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB. MAXIMUM SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS WITHIN 120 NM OF CENTER WITH THE HEAVIEST ACTIVITY CURRENTLY OVER THE SE QUADRANT. ISOLATED MODERATE AND STRONG CONVECTION IS NOTED ELSEWHERE WITHIN 240 NM OF CENTER. ILEANA IS GRADUALLY STRENGTHENING AND IS FORECAST TO BECOME A HURRICANE TONIGHT. THE CYCLONE WILL BEGIN TO MOVE OVER COOLER SEAS SURFACE WATERS LATE THU AND IS EXPECTED TO BEGIN TO WEAKEN. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP4/WTPZ24 KNHC FOR MORE DETAILS. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM NW COLOMBIA WESTWARD ACROSS THE CARIBBEAN SEA ALONG 10.5N TO THE PACIFIC COAST OF NORTHERN COSTA RICA...THEN TURNS SW TO 09N95W...THEN NW TO 14N104W WHERE THE TROUGH LOSES IDENTITY IN THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH TROPICAL CYCLONE ILEANA. THE MONSOON TROUGH BECOMES ESTABLISHED AGAIN SW OF ILEANA NEAR 14N113W AND CONTINUES SW TO 10N123W THEN WESTWARD TO 10N130W...THEN TURNS SLIGHTLY NW TO BEYOND 12N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION VERIFIED BY LIGHTNING DATA IS OBSERVED WITHIN 240 NM EITHER SIDE OF A LINE FROM 06N78W TO 14N104W. ...DISCUSSION... AN UPPER LEVEL TROUGH IS MOVING OVER THE NW COAST OF THE CONUS AND CONTINUES SW INTO THE DISCUSSION AREA FROM 32N137W TO 27N142W. A LOW LEVEL TROUGH IS NOW INDUCED FROM 33N136W TO 28N137W EMBEDDED WITHIN A BROADER LOW LEVEL RIDGE THAT DOMINATES THE AREA N OF 15N W OF 120W. NORTHEASTERLY SURFACE WINDS ARE EXPECTED TO CONTINUE FOR A COUPLE OF DAYS AT 15 TO 20 KT SW OF THE RIDGE...IN THE AREA FROM 12N TO 15N W OF 135W...WITH SEAS 7 TO 9 FT IN NE SWELL. AN UPPER LEVEL ANTICYCLONE IS OVER COLORADO WITH AN UPPER RIDGE EXTENDING SW INTO THE DISCUSSION AREA TO 31N120W. ANOTHER UPPER ANTICYCLONE IS CENTERED NEAR 18N135W WITH A RIDGE NE TO 25N128W...AND A RIDGE ALSO EXTENDS SW TO A CREST AT 13N144W. A WEAK SURFACE LOW IS DISSIPATING JUST W OF THE AREA NEAR 12N141W WITH THE ASSOCIATED DEBRIS MOISTURE NOW RETURNING NE AROUND THE RIDGE ACROSS THE TROPICS FROM 15N TO 20N W OF 137W. AN ILL-DEFINED UPPER CYCLONE IS OBSERVED AT 27.5N119W WITH AN UPPER TROUGH EXTENDING S TO A BASE AT 23N118W. THIS WEAK UPPER TROUGH IS NOT DETECTED BY THE GLOBAL MODELS...BUT MAY PLAY INTO THE STEERING OF THE ILEANA IN THE FEW DAYS AS THE CYCLONE MOVES NW AROUND THE PERIPHERY OF AN UPPER RIDGE THAT EXTENDS FROM THE ANTICYCLONE OVER ILEANA TO ANOTHER WEAK ANTICYCLONE OVER THE SOUTHERN TIP OF THE BAJA CALIFORNIA PENINSULA. MOST OF THE DEBRIS MOISTURE FROM ILEANA IS ADVECTED SW TO ALONG 10N BETWEEN 110W AND 123W...BUT SOME MOISTURE IS ALSO FANNING OUT IN THE UPPER ANTICYCLONIC FLOW N OF ILEANA ACROSS THE SOUTHERN BAJA PENINSULA AND GULF OF CALIFORNIA. OTHERWISE...THE UPPER LEVELS APPEAR VERY DRY TO THE W OF A LINE EXTENDING FROM THE BAJA PENINSULA AT 25N111W TO THE EQUATOR AT 130W. AN UPPER CYCLONE IS OVER THE NW CARIBBEAN AT 20N80W WITH AN UPPER TROUGH EXTENDING S ACROSS PANAMA TO BASE AT 06N79W. AN UPPER ANTICYCLONE...ASSOCIATED WITH ATLANTIC TROPICAL CYCLONE ISSAC...IS OVER THE N CENTRAL GULF OF MEXICO WITH AN UPPER RIDGE EXTENDING SW ACROSS OLD MEXICO TO A BROAD CREST OVER THE TROPICAL PACIFIC NEAR 13N96W. THE UPPER DIFFLUENCE BETWEEN THE CARIBBEAN UPPER CYCLONE AND THIS UPPER RIDGE IS SUPPORTING CONVECTION OVER CENTRAL AMERICA AND THE TROPICAL PACIFIC AS PREVIOUSLY DESCRIBED. THE RESULTANT DEBRIS MOISTURE IS ADVECTED SW TO ALONG 03N BETWEEN 80W AND 108W. ELSEWHERE AT THE LOW LEVELS...SOUTHWESTERLY MONSOONAL AT 20 TO 25 KT WINDS WITH SEAS 8 TO 11 FT ARE OBSERVED FROM 12N TO 18N BETWEEN 107W AND 116W...MERGING WITH THE SOUTHERLY WINDS OVER THE S SEMICIRCLE OF TROPICAL STORM ILEANA. GLOBAL MODELS SUGGEST THAT A SURFACE LOW WILL FORM ALONG THE MONSOON TROUGH NEAR 10N95W ON THU AND MOVE NW WITH CYCLONIC WINDS OF 20 TO 25 KT GRADUALLY EXPANDING OUT TO ABOUT 180 NM ON FRI MIXING WITH LONG PERIOD CROSS EQUATORIAL SOUTHWESTERLY SWELL AT 18 TO 20 SECONDS...THAT WILL PROPAGATE N TO ALONG 15N BETWEEN 88W AND 100W. $$ NELSON