000 AXPZ20 KNHC 192129 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC SAT SEP 19 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 2115 UTC. ...SPECIAL FEATURES... A SMALL 1006 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 21N111W... ABOUT 140 NM SSW OF THE SOUTHERN TIP OF BAJA CALIFORNIA...MOVING NW NEAR 10 KT. THIS SYSTEM HAS BECOME LESS ORGANIZED THROUGHOUT THE DAY AS VISIBLE IMAGES SHOW AN EXPOSED LOW-LEVEL CENTER WITH SCATTERED MODERATE CONVECTION CONFINED TO WITHIN 180 NM E OF THE CENTER. THIS SYSTEM STILL HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION DURING THE NEXT DAY OR SO BEFORE IT ENCOUNTERS STRONGER SOUTHWESTERLY UPPER LEVEL WINDS. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. ...TROPICAL WAVE... A TROPICAL WAVE EXTENDS THROUGH THE GULF OF TEHUANTEPEC ALONG 95W N OF 10N MOVING W 15 KT. THE WAVE IS POOLING MOSITURE IN AN UPPER DIFFLUENT ZONE BETWEEN A LOW OVER THE SOUTHWESTERN CARIBBEAN AND AN ANTICYCLONE OVER SOUTHERN MEXICO. AS A RESULT...SCATTERED MODERATE AND EMBEDDED ISOLATED STRONG CONVECTION EXISTS TO THE WEST OF THE WAVE FROM 8N-14N BETWEEN 95W-103W. ...THE ITCZ... THE INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE FROM 10N85W TO 13N100W TO 11N112W TO 12N127W TO 10N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS FROM 08N TO 15N BETWEEN 94W AND 104W. SIMILAR CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 111W AND 118W...AND WITHIN 50 NM EITHER SIDE OF THE AXIS FROM 127W TO 130W. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS W OF 135W. ...DISCUSSION... W OF 120W...DEEP LAYER RIDGING DOMINATES THE PATTERN ACROSS THE SUBTROPICS WITH THE ANTICYCLONE CENTERED NEAR 35N142W. THE PRESSURE GRADIENT BETWEEN THE ASSOCIATED SURFACE HIGH AND THE ITCZ IS PRODUCING AN AREA OF 20 KT NE TRADES BETWEEN THE ITCZ AND 22N W OF 130W. SIMILAR MAGNITUDE NLY WINDS ARE EVIDENT IN SCATTEROMETER DATA N OF 28N BETWEEN 127W AND 132W...SUPPORTED BY THE PRESSURE GRADIENT BETWEEN THE HIGH AND BROAD TROUGHING ASSOCIATED WITH THE REMNANT LOW OF MARTY AND LOW PRESSURE OVER THE SOUTHWESTERN UNITED STATES. THESE AREAS OF WIND ARE FORECAST TO WEAKEN OVER THE NEXT DAY OR TWO AS THE SURFACE HIGH TRACKS NORTHEASTWARD...WEAKENING THE RIDGE ACROSS THE AREA. NW SWELL IS SUBSIDING OVER THE N CENTRAL WATERS BUT A NEW BATCH OF NW SWELL...ORIGINATING FROM THE SYSTEM CURRENTLY N OF HAWAII... SHOULD MOVE INTO THE NW WATERS TOMORROW. E OF 120W... AT 19/2100 UTC...THE LAST ADVISORY WAS ISSUED ON MARTY AS IT HAS BEEN WITHOUT DEEP CONVECTION FOR SOME TIME. THE REMNANT LOW IS EXPECTED TO TRACK WESTWARD WITHIN THE LOW-LEVEL FLOW AND WILL LIKELY PRODUCE 20-25 KT WINDS NEAR THE CENTER OVER THE NEXT COUPLE OF DAYS. OTHERWISE...THE MAIN SYNOPTIC SCALE FEATURES CONSIST OF A MID TO UPPER-LEVEL ANTICYCLONE CENTERED OVER SOUTHERN MEXICO AND AN ELONGATED UPPER-LEVEL TROUGH EXTENDING FROM THE NORTHERN BAJA PENINSULA SOUTHWESTWARD. DEEP LAYER SLY FLOW N OF 15N BETWEEN 105W AND 115W IS TRANSPORTING TROPICAL MOISTURE NORTHWARD. TOTAL PRECIPITABLE WATER IMAGERY DEPICTS THIS MOIST SURGE WELL...SHOWING IT PROPAGATE NORTHWARD OVER THE GULF OF CALIFORNIA. ALTHOUGH THE ATMOSPHERE IS MOIST...DEEP CONVECTION IS CONFINED TO THE SPECIAL FEATURE...TROPICAL WAVE...AND ITCZ. MEANWHILE...THE SW SWELL EVENT WITH PERIODS IN THE 14-16 SECOND RANGE CONTINUE TO AFFECT THE PACIFIC COASTS OF MEXICO AND CENTRAL AMERICA. WAVE WATCH GUIDANCE SHOWS A NEW SLY SWELL TRAIN WITH A LEADING PERIOD OF 17-19 SECONDS REACHING THE COASTLINE TONIGHT AND SUN. GULF OF TEHUANTEPEC...SCATTEROMETER DATA INDICATE THAT NLY 20-25 KT FLOW IS OCCURRING OVER THE GULF OF TEHUANTEPEC. THIS IS LIKELY DUE TO THE PRESSURE GRADIENT BETWEEN A RIDGE OVER MEXICO AND TROUGHING OVER THE BAY OF CAMPECHE. GFS AND NAM MODELS SHOW THIS REGIME CONTINUING OVER THE NEXT COUPLE OF DAYS...WITH WINDS STRONGEST DURING THE OVERNIGHT AND MORNING HOURS WHEN DRAINAGE FLOW IS MAXIMIZED. $$ CANGIALOSI