000 AXPZ20 KNHC 200920 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC SUN SEP 20 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0745 UTC. ...SPECIAL FEATURES... A 1006 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 22N112W...ABOUT 140 NM SOUTH-SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA. THE LOW IS CURRENTLY MOVING NW NEAR 10 KT. THE 0500 UTC ASCAT AND 0154 UTC QUIKSCAT PASSES SHOWED WINDS IN THE 20 TO 30 KT RANGE WITHIN 90 NM NE SEMICIRCLE OF THE LOW CENTER. CONVECTION ASSOCIATED WITH THIS SYSTEM HAS DECREASED MARKEDLY OVERNIGHT AND THE CHANCES OF THE LOW DEVELOPING INTO A TROPICAL CYCLONE OVER THE NEXT 48 HOURS WILL BE DIMINISHING AS THE SYSTEM CONTINUES NW UNDER THE CORE OF A SOUTHEASTERLY UPPER JET AND APPROACHES COOLER SEA SURFACE TEMPERATURES. ...TROPICAL WAVE... A TROPICAL WAVE LIES ALONG 96W N OF 08N. THE WAVE IS MOVING W AROUND 10 KT. SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 360 NM W OF WAVE AXIS FROM 13N TO 16N AND 150 NM E OF WAVE AXIS N OF 14N. ...THE ITCZ... THE INTERTROPICAL CONVERGENCE ZONE CAN BE FOUND FROM 08N79W TO 13N95W TO 11N110W TO 12N120W TO 11N140W. SCATTERED MODERATE CONVECTION LIES WITHIN 90 NM S AND 30 NM N OF THE ITCZ AXIS E OF 80W...WITHIN 60 NM S OF THE AXIS AND N OF THE ITCZ AXIS TO THE COAST OF CENTRAL AMERICA BETWEEN 87W AND 93W...AND WITHIN 60 NM N AND 150 NM S OF ITCZ AXIS BETWEEN 104W AND 111W. ISOLATED MODERATE CONVECTION LIES WITHIN 60 NM EITHER SIDE OF THE ITCZ AXIS W OF 135W. ...DISCUSSION... W OF 120W... DEEP LAYER RIDGING DOMINATES THE PATTERN ACROSS THE SUBTROPICS WITH THE UPPER LEVEL ANTICYCLONE CENTERED NEAR 34N136W. THE PRESSURE GRADIENT BETWEEN THE ASSOCIATED 1027 MB SURFACE HIGH NEAR 38N137W THE ITCZ IS PRODUCING A SMALL AREA OF NE TRADES TO 20 KT W OF 136W BETWEEN 12N AND 17N THAT IS FORECAST TO DIMINISH BELOW 20 KT LATER TODAY AS THE SURFACE HIGH BEGINS TO WEAKEN AS THE NEXT MID LATITUDE TROUGH ENCROACHES ON IT FROM THE W. THIS TROUGH WILL PROVIDE A NEW BATCH OF NW SWELL TO NW WATERS BY LATE TODAY. AT 0600 UTC...SHIP WDC3786 NEAR 28N141W AND AN UNKNOWN SHIP NEAR 25N132W REPORTED NE WINDS IN THE 20 TO 25 KT RANGE. THESE WINDS ARE DUE TO THE PRES GRADIENT INDUCED BY THE WEAKENING COLD FRONT FROM MONTEREY CALIFORNIA TO 34N125W TO 33N134W CUTTING INTO THE SURFACE RIDGE. THEY ARE EXPECTED TO DIMINISH BELOW 20 KT DURING THE DAY TODAY AS THE FRONT DISSIPATES. FINALLY...THE REMNANT LOW OF MARTY LIES NEAR 23N120W UNDER A 35-40 KT SOUTHEASTERLY UPPER JET AND DRY MID TO UPPER LEVELS. THERE IS NO NOTABLE CONVECTION ASSOCIATED WITH THE SYSTEM AND IT IS EXPECTED TO DEGRADE TO A TROUGH MON. E OF 120W... LOW LEVEL MOISTURE CONVERGED NEAR THE ITCZ AND A TROPICAL WAVE ALONG 96W LIES IN A REGION OF BROAD UPPER LEVEL DIFFLUENCE BETWEEN AN ANTICYCLONE CENTERED NEAR 20N104W AND A LOW CENTERED NEAR 01N87W. THIS AREA OF DIFFLUENCE IS EXPECTED TO TRACK W WITH THE WAVE...MAKING CONVECTION NEAR THE WAVE AXIS LIKELY OVER THE NEXT FEW DAYS AS IT PULLS AWAY FROM THE COAST. SPEAKING OF THE COAST...17-19 SECOND PERIOD SOUTHERLY SWELL HAS ARRIVED ALONG THE COAST OF CENTRAL AMERICA FROM THE GULF OF TEHUANTEPEC EASTWARD ACCORDING TO THE NOAA WAVEWATCH. THE SOUTHERLY SWELL WILL CONTINUE FOR THE NEXT FEW DAYS...WITH PERIODS SUBSIDING SLIGHTLY TO THE 14-16 SECOND RANGE BY MON EVENING. GAP WINDS AND GULF OF CALIFORNIA... THE ASCAT PASS FROM 0318 UTC CONFIRMS NORTH WINDS CONTINUE TO BE IN THE 20 TO 25 KT RANGE WITHIN 90 NM S OF THE GULF OF TEHUANTEPEC. THESE WINDS ARE DUE TO THE PRESSURE GRADIENT BETWEEN A 1018 MB SURFACE HIGH NEAR 26N102W OVER MEXICO AND ITCZ RELATED TROUGHING TO THE SOUTH ENHANCED BY THE TROPICAL WAVE ALONG 96W. EXPECT THESE WINDS TO CONTINUE THROUGH SUN. THE PATTERN WILL CHANGE BY MON AS THE TROPICAL WAVE PASSES W AND A STRONG COLD FRONT DIVES THROUGH THE SOUTHWESTERN U.S. AND SOUTHERN PLAINS...CROSSING SOUTH OF THE RIO GRANDE BY TUE. THIS FRONT WILL DISRUPT THE HIGH PRES OVER NORTHERN MEXICO AND BRING N WINDS TO 20 KT IN THE NORTHERN GULF OF CALIFORNIA BY TUE. $$ SCHAUER CLARK