000 AXPZ20 KNHC 162156 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC SAT MAY 16 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2145 UTC. ...ITCZ... THE ITCZ AXIS IS ALONG POINTS 07N77W TO 10N92W TO 10N102W TO 12N110W TO 06N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED WITHIN 60 NM EITHER SIDE OF LINE FROM 05N80.5W TO 08N87W...AND ALSO WITHIN 150 NM EITHER SIDE OF LINE FROM 14N110W TO 07N118W...THEN NARROWS TO WITHIN 60 NM EITHER SIDE OF LINE FROM 06N121W TO 10N130W TO 06N140W. AN EMBEDDED TROUGH IS ANALYZED WITHIN THE ITCZ AXIS FROM 15N113W TO 08N115W WITH CYCLONIC TURNING NOTED AT 10N117W. ...DISCUSSION... ALOFT...AN UPPER LEVEL ANTICYCLONE IS ESTIMATED NEAR 04N140W WITH A LARGE AMPLITUDE RIDGE EXTENDING NE ALONG 35N130W AND CRESTING OVER CANADA NEAR 60N120W. IMMEDIATELY TO THE SE OF THIS LARGE RIDGE IS AN UPPER TROUGH THAT DISSECTS N AMERICA FROM NE TOM SW INTO THE DISCUSSION AREA FROM 32N110W THROUGH AN UPPER CYCLONE AT 24N122W WITH TROUGH CONTINUING SW TO BASE NEAR 12N131W. VERY DRY UPPER AIR IS INDICATED OVER MOST OF THE W PORTION...ROUGHLY TO THE W OF A LINE ALONG 12N140W TO 13N120W TO 28N99W. A QUASI STATIONARY UPPER ANTICYCLONE IS CENTERED NEAR 13N105W WITH A SHORTWAVE RIDGE EXTENDING NE ACROSS OLD MEXICO ALONG 20N100W TO A CREST AT 30N93W. UPPER DIFFLUENCE UNDER THIS BROAD RIDGE HAS BEEN ENHANCING CONVECTION ALONG AND N OF THE ITCZ BETWEEN 85W AND 122W WITH SOME OF THE DEBRIS MOISTURE SPREADING NE ACROSS OLD MEXICO TO THE S OF 26N AND SPILLING E ACROSS THE RIDGE AXIS OVER THE SW GULF OF MEXICO AND RETURNING OVER THE PACIFIC NEAR THE ISTHMUS OF TEHUANTEPEC. A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA AND COLOMBIA TO A CREST OVER THE COLOMBIA AND PANAMA BORDER. AN UPPER CUT OFF CYCLONE OVER THE W CUBA HAS AN UPPER TROUGH EXTENDING S ALONG 80W CROSSING THE EQUATOR AT 79W INTO AN UPPER CYCLONE NEAR 04S79W. THIS MID TO UPPER TROUGH SEPARATES THE FLOW ASSOCIATED WITH THE S AMERICAN RIDGE FROM THE TROPICAL E PACIFIC RIDGE DESCRIBED ABOVE. ITCZ CONVECTION IS ENHANCED ALONG THE E PERIPHERY OF PACIFIC RIDGE BETWEEN 85W AND 78W WITH THE DEBRIS MOISTURE ADVECTED NE ACROSS THE CENTRAL CARIBBEAN. AT THE LOW LEVELS...A RIDGE EXTENDS SE FROM 32N135W TO 16N105W. THE GRADIENT NE OF THE RIDGE IS BEGINNING TO RELAX EFFECTIVELY SHRINKING THE AREA OF NORTHERLY WINDS TO 20 KT AND SEAS TO 9 FT TO THE WATERS N OF 26N BETWEEN 128W AND 120W. THE GRADIENT SHOULD CONTINUE TO RELAX TONIGHT AS THE RIDGE WEAKENS AND RETRACTS W ALLOWING A BROAD LOW LEVEL TROUGH TO DRIFT W OVER THE AREA N OF 25N AND E OF 127W THROUGH MON. EXPECTING NORTHERLY WINDS TO 20 KT TO SET UP ALONG THE W SIDE OF THE TROUGH AS ITS SHIFT W ACROSS THE NORTHERN WATERS. A SMALL AREA OF NE TRADES CURRENTLY TO 20 KT ARE OBSERVED S OF THE RIDGE BUT ARE EXPECTED TO DIMINISH BELOW 20 KT TONIGHT AS THE RIDGE WEAKENS. GAP WINDS...A BROAD INVERTED TROUGH IS EXPECTED TO DOMINATE THE EASTERN GULF OF MEXICO EARLY NEXT WEEK AND A COLD FRONT WILL SWEEP SE ACROSS THE WESTERN GULF OF MEXICO SETTING UP THE CONDITIONS FOR N WINDS AT 20 KT TO BRIDGE THE ISTHMUS OF TEHUANTEPEC INTO THE GULF OF TEHUANTEPEC LATE SUN NIGHT INCREASING TO 25 TO 30 KT LATE MON. $$ NELSON