000 AXPZ20 KNHC 191600 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC SUN SEP 19 2010 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 1500 UTC. ...ITCZ... MONSOONAL S TO SW FLOW NOT DESCRIBED BY THE ITCZ DOMINATES THE DEEP TROPICS ACROSS THE AREA...WITH A MONSOON TROUGH EXTENDING FROM LOW PRES 1007 MB NEAR 17N105W 13N109W TO 14N122W TO LOW PRES 1008 MB NEAR 13N125W TO 09N140W. SCATTERED MODERATE CONVECTION WITHIN 180 NM S OF TROUGH BETWEEN 107W AND 117W AND WITHIN 90 NM S OF TROUGH BETWEEN 127W AND 135W. ...DISCUSSION... ALOFT... SW WINDS PREVAIL OVER NW PORTION OF AREA BETWEEN LONG WAVE TROUGH ALONG 133W NEARING OREGON COAST AND A SUBTROPICAL RIDGE EXTENDING WSW FROM ANTICYCLONE NEAR 26N119W TO BEYOND 19N140W. TROUGH WILL WEAKEN AND MOVE NE AS IT REACHES THE WEST COAST WHILE ANTICYCLONE AND RIDGE AXIS REMAIN NEARLY STATIONARY. PROMINENT ANTICYCLONE IN WESTERN GULF OF MEXICO NEAR 24N95W. DIVERGENT UPPER LEVEL FLOW SW OF THIS FEATURE IS ENHANCING DEEP CONVECTION ASSOCIATED WITH THE SURFACE MONSOON TROUGH E OF 115W. UPPER LEVEL WINDS REMAIN QUITE STRONG EXCEPT IN IMMEDIATE VICINITY OF THE MONSOON TROUGH...AND VERTICAL SHEAR IS PREVENTING MOST OF THE LOW PRESSURE AREAS FROM DEVELOPING INTO COHERENT LOWS WITH POTENTIAL TO BECOME TROPICAL CYCLONES. MODEL GUIDANCE SHOWS WINDS ALOFT DECREASING SOMEWHAT OVER THE NEXT COUPLE OF DAYS...WHICH COULD ALLOW A LOW CENTERED 150 MILES S OF MANZANILLO MEXICO TO BECOME A TROPICAL CYCLONE. THE CHANCE OF TC FORMATION IN THIS AREA RATED MEDIUM AT 40 PCT. SURFACE... TROUGH MENTIONED ABOVE SUPPORTING A WEAKENING COLD FRONT THAT EXTENDS FROM 32N128W TO 26N140W MOVING E AT 10-15 KT. THE FRONT WILL WEAKEN INTO FRONTAL TROUGH FROM 30N127W TO 26N140W NEXT 12- 24 HOURS...THEN DISSIPATE MON. SCATTEROMETER AND ALTIMETRY DATA SHOWS 15-20 KT WINDS AND 7-8 FT SEAS ASSOCIATED WITH THIS FRONT. WEAK RIDGING AHEAD OF THE FRONT COMBINED WITH LOW PRES OVER NW MEXICO AND BAJA CALIFORNIA HAS INCREASED NW TO N WINDS TO 20-25 KT N OF 23N E OF 120W TO W COAST OF BAJA CALIFORNIA. CONDITIONS ARE EXPECTED TO CHANGE LITTLE OVER THE NEXT 2 DAYS. MONSOON TROUGH MENTIONED ABOVE IN ITCZ SECTION DOMINATES REST OF THE BASIN. SCATTEROMETER DATA SHOWS FRESH S-SW WINDS SOUTH OF THE TROUGH AXIS EXTENDING AS FAR WEST AS 131W. SW WINDS ASSOCIATED WITH THE ACTIVE MONSOON TROUGH ARE BEING FOCUSED BY A STRING OF EMBEDDED LOWS IN THE TROUGH. THE LOW NEAR 17N105W APPEARS TO BE GAINING MOMENTUM AND GLOBAL MODELS INDICATE FURTHER DEVELOPMENT IS POSSIBLE. THE LOW IS FORECAST TO DRIFT NW AT EASTERN END OF THE MONSOON TROUGH OVER THE NEXT FEW DAYS. TROPICAL CYCLONE FORMATION IS POSSIBLE WITH THIS SYSTEM OVER THE NEXT 2-3 DAYS. MARINE... FRESH TO STRONG SW WINDS PERSIST WITHIN 150 NM S OF THE MONSOON TROUGH AXIS...AND ARE PRODUCING SEAS MAXING OUT TO NEAR 12 FEET BETWEEN 105W AND 110W. WINDS COULD INCREASE TO NEAR 30 KT BY 24 HOURS ACROSS THIS AREA AS THE LOW NEAR 17N105W BECOMES BETTER ORGANIZED. LARGE SWELLS WILL CONTINUE TO PROPAGATE FROM SW TO NE OVER A BROAD PORTION OF THE AREA THROUGH THE WEEKEND. $$ MUNDELL