000 AXPZ20 KNHC 150345 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SAT OCT 15 2011 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 0215 UTC. ...SPECIAL FEATURES... AT 15/0300 UTC...TROPICAL STORM IRWIN IS CENTERED NEAR 17.7N 106.4W MOVING S-SE OR 165 DEG AT 6 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB. MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP1/WTPZ21 KNHC FOR MORE DETAILS. LIMITED DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH IRWIN. A SMALL CLUSTER OF NUMEROUS MODERATE TO ISOLATED STRONG CONVECTION IS NOTED WITHIN 120 NM SW QUADRANT. ISOLATED MODERATE CONVECTION IS ELSEWHERE FROM 15N TO 19N BETWEEN 105W AND 110W. IRWIN WILL BE MOVING THROUGH A MARGINAL ENVIRONMENT FOR THE NEXT SEVERAL DAYS...CHARACTERIZED BY DRY MID-LEVEL AIR...THE COOL WAKE LEFT FROM HURRICANE JOVA...AND MODERATE TO STRONG VERTICAL SHEAR. THE OFFICIAL NHC INTENSITY FORECAST CALLS FOR IRWIN TO GRADUALLY WEAKEN TO A TROPICAL DEPRESSION IN ABOUT 96 HOURS AND A REMNANT LOW IN ABOUT 120 HOURS. ...ITCZ/MONSOON TROUGH... MONSOON TROUGH EXTENDS FROM A 1005 MB LOW PRES OVER GUATEMALA NEAR 15N89W TO 16N103W WHERE IT ENDS. IT THEN RESUMES SW OF TROPICAL STORM IRWIN FROM 15N111W TO 12N123W TO 14N130W TO 11N140W. SOUTH OF THE MONSOON TROUGH...NUMEROUS MODERATE TO ISOLATED STRONG FROM 12N TO 14N BETWEEN 90W AND 93W...AND N OF THE MONSOON TROUGH TO THE MEXICAN COAST BETWEEN 96W AND 98W. SCATTERED MODERATE FROM 10N TO 15N BETWEEN 97W AND 100W. SIMILAR CONVECTION IS NOTED IN THE MONSOONAL FLOW FROM 06N TO 10N BETWEEN 105W AND 11OW. ...DISCUSSION... A COLD FRONT IS MOVING ACROSS THE NW CORNER OF THE AREA AND EXTENDS FROM 30N136W TO BEYOND 25N140W. AN EARLIER SCATTEROMETER PASS INDICATED 20-25 KT NW WINDS BEHIND THE FRONT WITH HIGHER WINDS W OF THE AREA. SEAS ARE ALSO RUNNING UP TO 10 FT IN NW SWELL IN THIS SAME REGION. BY 12 HOURS...A RATHER SIGNIFICANT 1006 MB AREA OF LOW PRES WILL BE JUST N OF THE AREA NEAR 31N138W WITH A WEAKENING COLD FRONT EXTENDING FROM THE LOW INTO THE AREA FROM 30N134W TO 20N140W. MODEL GUIDANCE CONTINUES THE 20-25 KT WINDS BEHIND THE FRONT WHILE SEAS BUILD TO BETWEEN 9-14 FT IN NW SWELL. THE SWELL WILL ALSO PROPAGATE S REACHING TO 20N BY SAT NIGHT. THE LOW WILL WEAKEN TO 1007 MB AS IT MOVES TO NEAR 31N136W IN 48 HOURS WITH THE REMNANT FRONT STRETCHING FROM THE LOW INTO THE AREA FROM 30N130W TO 26N131W. WINDS WILL DIMINISH TO LESS THAN 20 KT IN 48 HOURS WHILE LINGERING NW SWELL RANGES FROM 8-11 FT W OF LINE FROM 26N131W TO 20N134W TO 17N140W. THE WEAK LOW PRES EMBEDDED IN THE MONSOON TROUGH AND PREVIOUSLY LOCATED NEAR 12N123W HAS DISSIPATED. HOWEVER...MODEL GUIDANCE CONTINUES TO INDICATE A FEW 20 KT SOUTHERLY WINDS S OF THE MONSOON TROUGH WITH SEAS OF 8-11 FT IN MERGING SW AND NW SWELL. VERY WEAK PRES GRADIENT EXISTS OVER WATERS N OF THE MONSOON TROUGH BETWEEN IRWIN AND THE COLD FRONT. A WEAK 1012 MB HIGH PRES IS ANALYZED ON THE 0000 UTC SURFACE MAP NEAR 21N119W. LITTLE CHANGE IS EXPECTED IN THIS WEATHER PATTERN THROUGH 48 HOURS AS RATHER STRONG LOW PRES AFFECTS THE NW PORTION OF THE AREA AND TROPICAL CYCLONE IRWIN MOVES ACROSS OPEN WATERS AND AWAY FROM MEXICO. AN EARLIER WINDSAT SCATTEROMETER PASS INDICATED 20-25 KT NORTHERLY WINDS IN AND DOWNSTREAM OF THE GULF OF TEHUANTEPEC AROUND A BROAD AREA OF 1005 MB LOW PRES CENTERED OVER CENTRAL GUATEMALA ALONG WITH 8-11 FT SEAS IN THE GULF OF TEHUANTEPEC. AN AREA OF FRESH TO STRONG MONSOONAL FLOW PERSISTS OFF THE COASTS OF CENTRAL AMERICA AND SE MEXICO PARTICULARLY N OF 07N E OF 95W...AND FROM 03N TO 07N BETWEEN 78W AND 90W WHERE SEAS ARE UP TO 14 FT IN THIS AREA OF PERSISTENT SW FETCH. THESE WINDS AND SEAS WILL PERSIST OVER THE SAME GENERAL AREA DURING THE NEXT 24-48 HOURS AS THE BROAD AREA OF LOW PRES REMAINS NEARLY STATIONARY. AS THIS LOW PRES AREA OVER GUATEMALA LINGERS...VERY HEAVY RAINFALL WILL CONTINUE OVER PORTIONS OF THE PACIFIC COASTS OF SOUTHEASTERN MEXICO...GUATEMALA...EL SALVADOR...SOUTHERN HONDURAS AND NICARAGUA RESULTING IN LIFE-THREATENING FLASH FLOODS AND MUD SLIDES. THE REMAINDER OF THE REGIONAL WATERS ARE DOMINATED BY MERGING NW AND SW SWELL. THIS SWELL EVENT WILL GRADUALLY SUBSIDE FROM THE NW TO SE THROUGH THE NEXT 24-48 HOURS...WHILE THE NEW SET OF NW SWELL ENTERING THE AREA MOVES SE. $$ GR/JL