000 AXPZ20 KNHC 030337 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC WED SEP 03 2008 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 0315 UTC. ...SPECIAL FEATURE... TROPICAL DEPRESSION KARINA 1002 MB AT 20.0N 112.6W AT 0300 UTC MOVING WNW AT 6 KNOTS WITH MAXIMUM SUSTAINED WINDS OF 30 KT GUSTING TO 40 KT. DEEP CONVECTIVE TOPS EXTENDING OUT TO ALMOST 180 NM IN THE W QUADRANT EARLIER THIS EVENING HAVE BEEN SHORN APART BY WHAT CIMSS SHOWS AS AT LEAST 20 KT EASTERLY SHEAR. LATEST SATELLITE IMAGERY SHOWS THE NEAREST DEEP CONVECTION NOW MORE THAN A DEGREE REMOVED FROM THE LOW-LEVEL CENTER. BESIDES THE SHEAR...KARINA IS IN THE PROCESS OF MOVING FROM 28C TO 25- 26C SEA SURFACE TEMPERATURES...WHICH SHOULD CAUSE ANY CONVECTION WHICH PERSISTS TO DECREASE. THE COMBINATION OF A HIGH SHEAR ENVIRONMENT AND COOLING OCEAN TEMPERATURES SHOULD RESULT IN DISSIPATE WITHIN THE NEXT 24 TO 36 HOURS. ...ITCZ... ITCZ AXIS ALONG 09N84W TO 11N106W TO 10N120W TO 07N140W. WIDELY SCATTERED MODERATE CONVECTION WITHIN 120 NM EITHER SIDE OF AXIS BETWEEN 93W AND 115W. WIDELY SCATTERED MODERATE CONVECTION WITHIN 90 NM S OF AXIS BETWEEN 121W AND 136W. ...DISCUSSION... A DEEP TROUGH OF LOW PRESSURE DROVE A STRONG COLD FRONT RATHER FAR S IN THE NE PACIFIC AND THEN INTO THE WESTERN STATES THIS PAST WEEKEND AND LEFT A STRONG SURFACE RIDGE IN ITS WAKE. THE ENHANCED PRESSURE GRADIENT BETWEEN LOW PRESSURE OVER THE SW CONUS AND THE SURFACE RIDGE OVER THE NE PACIFIC BROUGHT ABOUT THE DEVELOPMENT OF NW TO N GALE FORCE WINDS OFFSHORE THE CALIFORNIA COAST WHICH PERSIST EVEN NOW. A WELL-DEFINED NORTHERLY SWELL TRAIN HAS SINCE PROPAGATED WELL S INTO THE TROPICAL E PACIFIC WATERS...WITH THE WAVE FRONT NOW REACHING A LINE FROM ROUGHLY 22N110W TO 16N140W. SEAS OF 8 TO 11 FT IN LONG PERIOD NW TO N SWELL PREVAIL NW OF THAT LINE E OF 127W WHILE N TO NE LONG PERIOD SWELL LIES W OF 127W. MODEL GUIDANCE INDICATES THAT THE SWELL SHOULD CONTINUE TO SPREAD SOUTHWARD OVER THE BASIN...BUT WAVE HEIGHTS SHOULD BEGIN TO SUBSIDE AS GALES OFFSHORE THE U.S. W COAST ABATE. ELSEWHERE...EARLIER QUIKSCAT DATA SHOWED A BROAD AREA OF S TO SW WINDS OF 20 KT LYING S OF THE ITCZ TO NEAR THE EQUATOR FROM 88W TO 134W. MEANWHILE...LONG PERIOD SW SWELL COMING OUT OF THE SOUTHERN HEMISPHERE CONTINUES TO ARRIVE OVER THE FAR SOUTHERN WATERS AS WELL AS THE MEXICAN AND CENTRAL AMERICAN COASTS. IN FACT...SEVERAL SHIP REPORTS INDICATED 8 TO 9 FT SEAS IN SW SWELL IMMEDIATELY OFFSHORE THE S COAST OF MEXICO EARLIER THIS EVENING. NOAA WAVEWATCH III GUIDANCE SUGGESTS THAT 8 TO 11 FT WAVE HEIGHTS LIE ROUGHLY S OF 12N BETWEEN 88W AND 134W...WITH THE PEAK HEIGHTS WITHIN ABOUT 300 NM OF 10N110W. ALTHOUGH SW SWELL SHOULD GRADUALLY SUBSIDE OVER THE NEXT DAY OR TWO...MODELS SHOW ANOTHER WELL-DEFINED AREA OF LONG PERIOD SW SWELL REACHING THE FAR SOUTHERN WATERS LATE THIS WEEK AND WEEKEND. IN ADDITION TO THE SW SWELL...MODEL GUIDANCE STRENGTHENS LOW PRESSURE NEAR AND JUST OFFSHORE THE S COAST OF MEXICO THE NEXT FEW DAYS...WHICH RESULTS IN A CONTINUATION OF THE ANOMALOUS LOW- LEVEL SW TO W FLOW WHICH HAS DOMINATED MUCH OF THE SOUTHERN HALF OF THE BASIN SINCE LAST WEEK. SOME OF THE SW TO W FLOW COULD BE RATHER STRONG...WHICH COULD RESULT IN LOCALLY HIGHER SEAS. $$ KIMBERLAIN