000 AXPZ20 KNHC 101602 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC SAT OCT 10 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1515 UTC. ...SPECIAL FEATURE... THE AREA OF LOW PRESSURE NOW LOCATED NEAR 16N108W HAS MOVED MORE TO THE WEST OVER THE PAST 12 HOURS AND IS BECOMING BETTER ORGANIZED PER RECENT VISIBLE SATELLITE IMAGERY. SCATTERED MODERATE TO STRONG CONVECTION ORGANIZED IN TWO MAIN BANDS ARE ROTATING CYCLONICALLY AROUND THE CENTER. THE FIRST BAND WAS WITHIN 60 NM OF AN ARC THROUGH 16N110W 14N108.5W TO 14N107W... AND THE SECOND BAND WAS WITHIN 45 NM OF AN ARC THROUGH 14.5N103W 16N105.5W TO 16N107W. THE EDGE OF A 1242 UTC HIGH RESOLUTION QUIKSCAT PASS INDICATED THAT HE AREA OF LOW PRESSURE WAS STILL ELONGATED ALONG A NNW-SSE AXIS. AT THE UPPER LEVELS THE LOW IS SITUATED WITHIN AND JUST TO THE SOUTH OF A NARROW RIDGE AXIS. THE UPPER LEVEL WESTERLY WINDS NOTED EARLIER HAVE BEEN REPLACED BY GENERALLY LIGHT WINDS. THE LOW IS FORECAST TO MOVE SLOWLY NW TO N TO THE SOUTH OF CABO SAN LUCAS OVER THE NEXT COUPLE OF DAYS AS A SHORT WAVE TROUGH CURRENTLY OFF THE CALIFORNIA COAST MOVES EASTWARD TO THE NORTH OF THE LOW. THERE IS NOW A HIGH CHANCE...GREATER THAN 50 PERCENT THAT THE LOW MAY FORM INTO A TROPICAL CYCLONE OVER THE NEXT 48 HOURS. ...TROPICAL WAVE... A TROPICAL WAVE ALONG 89W N OF 06N IS MOVING WEST AT 10 TO 15 KT. THIS WAVE IS INTERACTING WITH AN UPPER LOW NEAR 15N92W. DIVERGENCE ASSOCIATED WITH THE UPPER LOW ALONG WITH 20 KT SW FLOW TO THE SOUTH OF THE ITCZ IS ENHANCING SCATTERED MODERATE CONVECTION ALONG THE WAVE...WITH ISOLATED STRONG CONVECTION ALONG THE NICARAGUAN COAST. ...ITCZ... THE ITCZ AXIS WAS CENTERED ALONG 09N85W TO 12N100W TO 12N118W TO 14N131W...THEN RESUMES FROM 13N135W TO 10N140W. SCATTERED MODERATE CONVECTION IS ALONG THE ITCZ AXIS BETWEEN 87W AND 91W. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS WITHIN 60 NM N OF AXIS BETWEEN 105W AND 110W...AND WITHIN 50 NM EITHER SIDE OF AXIS BETWEEN 114W AND 117W. SCATTERED MODERATE CONVECTION IS ALSO NOTED WITHIN 70 NM N OF AXIS W OF 125W. ...DISCUSSION... FAIRLY PROGRESSIVE PATTERN IS IN PLACE N OF 20N WITH A RIDGE- TROUGH-RIDGE PATTERN IN PLACE. FIRST RIDGE ALONG 136W N OF 20N IS SWEEPING E AT 15 KT. DOWNSTREAM SHORT WAVE TROUGH EXTENDS FROM NORTHERN CALIFORNIA TO 23N125W IS MOVING EAST AT 20 KT. DOWNSTREAM FLAT RIDGE COVERS NORTHERN MEXICO AND IS IN PHASE WITH AN ELONGATED MID TO UPPER LEVEL RIDGE AXIS WHICH EXTENDS FROM CENTRAL MEXICO AND IS ORIENTED EAST TO WEST ALONG 17N/18N THROUGH 140W. SUBSIDENT WESTERLY FLOW ON THE NORTH SIDE OF THE UPPER RIDGE IS MAINTAINING FAIRLY DRY AIR N OF THE ITCZ BETWEEN 105W TO 120W. MEANWHILE DIVERGENT FLOW ALOFT BETWEEN THE SHORT WAVE TROUGH AND THE WESTERN EDGE OF THE UPPER RIDGE IS PROVIDING EXHAUST TO ENHANCE CONVECTION ALONG THE ITCZ BETWEEN 130W AND 135W. A WEAK SURFACE TROUGH IS ANALYZED WITHIN THIS CONVECTION NEAR 133W. A 1422 UTC QUIKSCAT PASS SHOWED A SHRINKING AREA OF TRADES BETWEEN THE ITCZ AND 17N ON THE SOUTHERN PERIPHERY OF A BROAD SURFACE RIDGE N OF THE AREA. THESE WINDS WILL DIMINISH THROUGH TODAY AS THE RIDGE WEAKENS AHEAD OF A COLD FRONT APPROACHING THE AREA FROM THE CENTRAL PACIFIC. THE FRONT WILL REACH A POSITION FROM 30N135W TO 23N140W BY LATE SUN. LONG PERIOD NE SWELL IN THE AREA OF TRADES ROUGHLY FROM 10N TO 20N W OF 120W WILL DECAY THROUGH TONIGHT...JUST AHEAD OF THE ARRIVAL OF NW SWELL TO 10 FT PUSHES INTO THE DISCUSSION AREA SUNDAY BEHIND THE COLD FRONT. $$ COBB