000 AXPZ20 KNHC 170301 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SAT SEP 17 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 0245 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS W FROM THE N COAST OF COLOMBIA AT 11N76W TO THE BORDER OF COSTA RICA AND NICARAGUA...THEN CONTINUES NW PARALLELING THE COAST OF CENTRAL AMERICA TO 16N103W...THEN TURNS SW TO 1011 MB LOW PRES AT 12N131W...WITH THE TROUGH AXIS THEN TURNING SW AND CONTINUING BEYOND 10N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION...ACCOMPANIED BY NUMEROUS LIGHTNING STRIKES...IS OBSERVED WITHIN 60 NM OF THE COAST OF CENTRAL AMERICA FROM 09N TO 15N...AND JUST BEGINNING TO MOVE OFFSHORE THE MEXICAN COAST FROM 20N TO 25N. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED OVER THE PACIFIC S OF THE MONSOON TROUGH AXIS...WITHIN 180 NM EITHER SIDE OF A LINE FROM 07N80W TO 09N103W. SIMILAR CONVECTION IS NOTED WITHIN 210 NM EITHER SIDE OF A LINE FROM THE MEXICAN COAST AT 19N104W TO 12N116W TO 10N140W. ...DISCUSSION... AN UPPER LEVEL LONGWAVE TROUGH DOMINATES THE W COAST OF N AMERICA WITH AN EMBEDDED SHORTWAVE ALONG 32N116W TO 25N128W TO A BASE AT 12N137W...CUTTING OFF AN UPPER CYCLONE W OF THE AREA AT 23N151W. A SMALL UPPER ANTICYCLONE IS IMMEDIATELY NW OF THE SHORTWAVE TROUGH AT 33N146W WITH AN UPPER RIDGE EXTENDING SE TO A SHARP CREST AT 30N138W. UPPER MOISTURE IS SPREADING SE IN THE WAKE OF THE SHORTWAVE TROUGH WITH ITS SOUTHERN EXTENT ALONG 33N TO THE E OF 138W TO ACROSS SOUTHERN CALIFORNIA. OTHERWISE THE UPPER LEVELS APPEAR DRY TO THE W OF A LINE FROM 30N105W TO 12N140W. AN UPPER ANTICYCLONE IS OVER CENTRAL OLD MEXICO AT 22N101W WITH A RIDGE EXTENDING SW OVER THE TROPICAL PACIFIC TO A SHARP CREST AT 14N131W...AND A RIDGE ALSO EXTENDS SE TO 13N92W. UPPER DIFFLUENCE ALONG THE SW RIDGE IS ENHANCING THE PREVIOUSLY DESCRIBED CONVECTION THAT EXTENDS SW FROM THE MEXICAN COAST AT 19N104W. SOME OF THE DEBRIS MOISTURE IS ADVECTED N AND NE ACROSS THE UPPER RIDGE WITH THE MOST DENSE MOISTURE TURNING NE ACROSS WESTERN OLD MEXICO FROM 18N TO 26N. AN UPPER TROUGH ALSO DOMINATES THE E COAST OF N AMERICA... CONTINUING SW ACROSS THE FLORIDA STRAITS THROUGH AN UPPER CYCLONE AT 21N84WSW...ACROSS GUATEMALA TO BASE AT 08N93W. AN UPPER ANTICYCLONE IS OVER THE W CARIBBEAN AT 12N80W WITH ITS ENVELOPE OF ANTICYCLONIC FLOW EXTENDING S OF THE TROPICS BETWEEN 75W AND 90W. A LOW LEVEL TROUGH IS MOVING ACROSS NICARAGUA AND HONDURAS UNDER THE UNDER THE ASSOCIATED UPPER RIDGE RESULTING IN CONSIDERABLE CONVECTION YESTERDAY AFTERNOON. DEBRIS MOISTURE FROM THIS CONVECTION OVER CENTRAL AMERICA...AND OVER THE PACIFIC S OF THE MONSOON TROUGH...IS SPREADING SW TO ALONG 03N BETWEEN 80W AND 110W. AT THE LOW LEVELS...1028 MB HIGH PRESSURE IS CENTERED NW OF THE AREA AT 35N145W WITH A RIDGE EXTENDING SE FROM 30N141W TO 20N110W. A SMALL AREA OF NORTHEASTERLY TRADES AT 15 TO 20 KT...SEAS TO 8 FT...CONTINUES FROM 11N TO 19N W OF 128W WITH THE AFFECTED AREA EXPECTED TO SHRINK TO WITHIN THE AREA BOUNDED BY 11N TO 15N W OF 135W BY LATE SUN. SOUTHWESTERLY SURFACE WINDS AT 15 TO 20 KT...WITH COMBINED SEAS TO 9 FT...ARE OBSERVED IN THE AREA FROM 07N TO 10N BETWEEN 110W AND 120W. THESE SOUTHWESTERLY WINDS ARE EXPECTED TO CONTINUE WITHIN ABOUT 420 NM SE OF THE MONSOON TROUGH AXIS WHICH SHOULD EXTEND FROM 16N110W TO NEAR 10N128W BY LATE SUN. GAP WINDS...NORTHERLY WINDS ARE AT ALREADY AT 15 TO 20 KT IN THE CHIVELA PASS AND EXPECTED TO SURGE INTO THE GULF OF TEHUANTEPEC BY SUNRISE...INCREASING TO 20 TO 25 KT AROUND SUNRISE ON SUN... AND DIMINISHING TO LESS THAN 20 KT LATE MON. $$ NELSON