000 AXPZ20 KNHC 200323 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SUN SEP 20 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0300 UTC. ...SPECIAL FEATURES... A SMALL 1006 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 21N111W... ABOUT 140 MILES SOUTH-SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA...MOVING NW NEAR 10 KT. ALTHOUGH SHOWER AND THUNDERSTORM ACTIVITY IS POORLY ORGANIZED AT THIS TIME...THERE IS STILL SOME OPPORTUNITY FOR DEVELOPMENT BEFORE THE SYSTEM REACHES COOLER WATERS ON SUNDAY. THERE IS A MEDIUM CHANCE...30 TO 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 09N MOVING W AROUND 15 KT. THE WAVE COMBINED WITH A DIFFLUENT PATTERN ALOFT IS ENHANCING CONVECTION OVER SE MEXICO AND THE YUCATAN PENINSULA. ...THE ITCZ... THE INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE 07N78W TO 13N96W TO 13N125W TO 11N140W. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM S OF AXIS FROM 102W TO 107W. SIMILAR CONVECTION IS WITHIN 100 NM EITHER SIDE OF AXIS FROM 111W TO 114W...AND FROM 09N TO 12N W OF 129W. ...DISCUSSION... W OF 120W...DEEP LAYER RIDGING DOMINATES THE PATTERN ACROSS THE SUBTROPICS WITH THE ANTICYCLONE CENTERED NEAR 35N141W. THE PRESSURE GRADIENT BETWEEN THE ASSOCIATED SURFACE HIGH AND THE ITCZ IS PRODUCING AN AREA OF 20 KT NE TRADES BETWEEN THE ITCZ AND 20N W OF 130W. THESE WINDS ARE FORECAST TO DIMINISH BELOW 20 KT IN ABOUT 24 HOURS 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 SHOULD REACH THE FAR NW PORTION OF THE AREA SUN MORNING. E OF 120W... AT 19/2100 UTC...THE LAST ADVISORY WAS ISSUED BY THE NATIONAL HURRICANE CENTER ON MARTY. SATELLITE IMAGERY CURRENTLY SHOWS A LARGE SWIRL OF LOW CLOUDS NEAR 23.0N 119.5W. THE REMNANT LOW IS EXPECTED TO TRACK W-NW AT AROUND 10 KT WITHIN THE LOW-LEVEL FLOW AND IS PREDICTED TO DISSIPATE BY THE COMPUTER MODELS IN ABOUT 48 HOURS. THIS SYSTEM WILL LIKELY PRODUCE 20-25 KT WINDS AND SEAS TO 9 FT MAINLY N OF 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 TO NEAR 25N132W. GULF OF TEHUANTEPEC...AN EARLIER QSCAT PASS SHOWED NLY 20-25 KT FLOW OCCURRING OVER THE GULF OF TEHUANTEPEC. THIS IS MOST 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. THE SW SWELL EVENT WITH PERIODS IN THE 14-16 SECOND RANGE CONTINUE TO AFFECT THE PACIFIC COASTS OF MEXICO AND CENTRAL AMERICA. NOAA WAVE WATCH MODEL SHOWS A NEW SLY SWELL TRAIN WITH A LEADING PERIOD OF 17-19 SECONDS REACHING THE COASTLINE TONIGHT AND SUN. $$ GR/JC