000 AXPZ20 KNHC 172152 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC MON DEC 17 2012 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2145 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS W FROM THE COLOMBIAN COAST AT 06N77W TO 07N96W...THEN TURNS NW TO 09N100W...THEN SW TO 06N110W WHERE LOW LEVEL WINDS INDICATE A TRANSITION TO AN ITCZ WHICH CONTINUES W ALONG 06N TO BEYOND 140W. BROKEN-OVERCAST LOW-MID LEVEL CLOUDS WITH ISOLATED MODERATE CONVECTION IS NOTED WITHIN 120 NM OF EITHER SIDE OF A LINE FROM 05N77W TO 05N117W. ISOLATED MODERATE TO STRONG CONVECTION IS NOTED WITHIN 30 NM EITHER SIDE OF A LINE FROM 09N131W TO 07N140W. ...DISCUSSION... ALOFT...AN UPPER TROUGH IS PROGRESSING ACROSS THE NE PORTION WITH ITS AXIS EXTENDING SW FROM E TEXAS ACROSS CENTRAL OLD MEXICO TO 21N109W. AN UPPER CYCLONE HAS CUT OFF JUST W OF THE AREA AT 21N142W. A SHORTWAVE UPPER RIDGE HAS BUILT N ACROSS THE DISCUSSION AREA BETWEEN 120-135W WITH THE RIDGE CURRENTLY CRESTING AT 31N135W. THIS CHANGE IN THE UPPER FLOW NOW DIRECTS A MOISTURE PLUME...ORIGINATING IN THE CENTRAL PACIFIC...NE UNDER THE UPPER RIDGE. ONLY A NARROW BAND OF THE MOISTURE CONTINUES TO STREAM E ALONG 20N TURNING NE AHEAD OF THE UPPER TROUGH OVER THE GULF OF MEXICO. A LARGE AREA OF UPPER DRY AIR IS SPREADING E ACROSS THE SUBTROPICS TO THE E OF 120W, AN INVERTED UPPER TROUGH IS OBSERVED OVER THE DEEP TROPICS TO THE S OF 09N ALONG 119W AND SEPARATES THE UPPER LEVEL FLOW ACROSS THE TROPICAL PORTION OF THE DISCUSSION AREA. THE UPPER LEVEL ANTICYCLONIC NORTHWESTERLY FLOW NOTED OVER THE DEEP TROPICS TO THE W OF THIS INVERTED TROUGH IS ADVECTING MOISTURE SE TO ALONG 02N BETWEEN 120-130W. AN UPPER ANTICYCLONE IS CENTERED AT 14N103W WITH AN UPPER RIDGE EXTENDING SW TO A SHARP CREST AT 11N116W. AN UPPER RIDGE ALSO EXTENDS E FROM THE ANTICYCLONE TO OVER CENTRAL AMERICA AT 15N91W. THE UPPER FLOW HAS BECOME WEAK OVER THE DEEP TROPICS S OF 07N BETWEEN 85-95W WITH ONLY THE ISOLATED MONSOON CONVECTION ENHANCED AS PREVIOUSLY DESCRIBED. LOW LEVELS...A SURFACE RIDGE EXTENDS FROM 30N140W TO 15N105W. SURFACE WINDS ARE AT 5-10 KT ACROSS THE SUBTROPICAL WATERS WITH SEAS 4-7 FT. NE TRADES CONTINUE AT 15-20 KT TO THE S OF THE RIDGE ACROSS THE WATERS S OF 22N W OF 107W WITH SEAS 7-10 FT IN NE SWELL THAT MIXES WITH NW SWELL ACROSS THE WATERS E OF 120W... AND ALSO MIXES WITH CROSS EQUATORIAL SE SWELL ACROSS THE WATERS S OF 07N W OF 110W. NORTHERLY WINDS ALONG THE FAR EASTERN PERIPHERY OF THE SURFACE RIDGE ARE 15-20 KT...EXCEPT FOR A FEW REPORTS OF 20-25 KT...OVER THE SOUTHERN GULF OF CALIFORNIA WITH THESE WINDS NOTED AS FAR S AS 21N107W. THE GRADIENT IS EXPECTED TO RELAX TONIGHT WITH THE AREA OF ENHANCED WINDS SHRINKING FROM 10-17N W OF 120W EARLY TUE. A WEAK TROUGH IS STILL EXPECTED TO BRIEFLY DEVELOP TUE OVER THE SW PORTION...ROUGHLY FROM 10-17N W OF 136W...MAINTAINING A NE-E 20-25 KT WIND SHIFT. A STRONG...BUT DRY...COLD FRONT WILL SWEEP RAPIDLY SE INTO THE SUBTROPICAL WATERS LATE TONIGHT ACCOMPANIED BY N-NE 20-25 KT WINDS...WITH SEAS BUILDING 8-13 FT W OF THE FRONT. THESE NW 20-25 KT WINDS AND SEAS 8-10 FT WILL ARRIVE AT THE NW COAST OF THE BAJA PENINSULA AROUND TUE EVENING. THE GRADIENT IS EXPECTED TO RELAX FROM THE NW TO SE BEGINNING TUE NIGHT INTO EARLY WED WITH THE SURFACE WINDS CLOCKING TO THE NE AND DIMINISHING TO 15-20 KT ALONG THE BAJA PENINSULA TO THE N OF 25N. THE NW SWELL WILL PROPAGATE SE ACROSS THE ENTIRE AREA NW OF A LINE FROM THE CENTRAL BAJA PENINSULA TO 08N140W MIXING WITH THE NE AND SE TRADE SWELL ACROSS THE TROPICS. GULF OF CALIFORNIA...WINDS WILL BECOME SW AT 20-25 KT OVER THE NORTHERN GULF WATERS TUE IN ADVANCE OF THE FRONT WHICH WILL PASS S OF THE GULF WATERS WED NIGHT WITH NW 20-25 KT POST-FRONTAL WINDS CONTINUING THROUGH EARLY THU...THEN DIMINISHING 15-20 KT THU EVENING AND TO 15 KT ON FRI. THE NEXT COLD FRONT ENTERS THE NW WATERS AT 30N140W ON FRI MORNING WITH SEAS BUILDING TO A HIGH AS 18 FT BRIEFLY BEHIND THE FRONT ON FRI NIGHT. THIS NEXT ROUND OF NW SWELL...RESULTING TO COMBINED SEAS OF 8-12 FT...WILL REACH THE BAJA PENINSULA SAT NIGHT. GULF OF TEHUANTEPEC...LIGHT AND VARIABLE SOUTHERLY WINDS WILL GIVE WAY TO NORTHERLY 15-20 KT DRAINAGE WINDS JUST BEFORE SUNRISE ON TUE...AND CONTINUE THROUGH LATE WED...WITH THE FLOW BECOMING LIGHT SOUTHERLY ON WED NIGHT INTO LATE MORNING ON THU. NORTHERLY WINDS WILL SURGE THROUGH THE CHIVELA PASS INTO THE GULF OF TEHUANTEPEC ON THU AFTERNOON...RAPIDLY BUILDING TO GALE FORCE THU EVENING WITH NEAR STORM CONDITIONS EXPECTED AROUND SUNRISE FRI. $$ NELSON