000 AXPZ20 KNHC 290953 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC SAT DEC 29 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0945 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS W ACROSS THE SW CARIBBEAN ALONG 10N TO THE COAST OF COSTA RICA AT 10N83W...THE CONTINUES W-SW ACROSS THE PACIFIC TO 08N110W WHERE LOW LEVEL WINDS INDICATE A TRANSITION TO AN ITCZ. THE ITCZ THEN WIGGLES W BETWEEN 07-09N TO BEYOND 08N140W. ISOLATED MODERATE TO STRONG CONVECTION...WITH OCCASIONAL LIGHTNING STRIKES...IS OBSERVED FROM 06N TO 09N E OF 84W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED ALONG THE MONSOON TROUGH AXIS AND THE ITCZ AXIS WITHIN 30 NM EITHER SIDE OF LINES FROM 07.5N98W TO 08N104W AND FROM 07N109W TO 09N115W. SCATTERED MODERATE CONVECTION IS DISSIPATING WITHIN 120 NM OF 07N91W...AND IS ALSO OBSERVED WITHIN 60 NM EITHER SIDE OF A LINE FROM 08N124W TO 08N134W. THE ITCZ IS STRETCHING N NEAR 10N125W WHERE A 1008 MB SURFACE LOW IS EXPECTED TO DEVELOP TONIGHT...AND PERSIST FOR A DAY OR SO. EXPECT CYCLONIC WINDS AT ONLY 15-20 KT WITHIN ABOUT 90 NM OF THE LOW WHICH WILL HAVE A BROAD INVERTED TROUGH EXTENDING NE TO NEAR 16N115W ON SUN. EXPECT A NE-E-SE 15-20 KT WIND SHIFT ALONG THE TROUGH AXIS. ...DISCUSSION... ALOFT...AN UPPER SHORTWAVE TROUGH IS BECOMING NEGATIVE TILT WITH TIME AS IT MOVES E ACROSS THE WESTERN PORTION OF THE AREA WITH ITS MEAN AXIS CURRENTLY EXTENDING FROM 32N123W TO A BASE AT 19N118W. A NARROW BAND OF UPPER MOISTURE PRECEDES THE TROUGH AND IS MOVING ACROSS SOUTHERN CALIFORNIA WHILE A BAND OF DRY UPPER AIR IS INDICATED ACROSS THE NORTHERN BAJA PENINSULA AND THE NORTHERN GULF OF CALIFORNIA. AN UPPER ANTICYCLONE IS CENTERED OVER COLOMBIA AT 07N72W WITH A RIDGE AXIS EXTENDING W-NW TO A CREST OVER THE TROPICAL PACIFIC AT 12N105W. UPPER DIFFLUENCE S OF THIS RIDGE IS ENHANCING THE ISOLATED CLUSTERS OF CONVECTION PREVIOUSLY MENTIONED BETWEEN COLOMBIA AND 104W...WITH THE DEBRIS MOISTURE FROM THE CONVECTION E OF 90W ADVECTED NE ACROSS CENTRAL AMERICA TO THE E OF 88W. BROAD ANTICYCLONIC UPPER WESTERLY FLOW IS OBSERVED OVER THE DEEP TROPICS S OF 10N BETWEEN 107-137W AND COMBINED WITH THE UPPER TROUGH AND RIDGE PATTERN PREVIOUSLY DESCRIBED SETS UP AN AREA OF WEAK UPPER DIFFLUENCE SUPPORTING THE ITCZ CONVECTION NEAR 08N112W. UPPER DEBRIS MOISTURE ORIGINATING FROM ITCZ CONVECTION BETWEEN 125-148W IS ADVECTED NE ACROSS THE AREA FROM 05-17N BETWEEN 120-135W. THIS MOISTURE MERGES WITH ADDITIONAL UPPER MOISTURE ADVECTED N AND NE AROUND THE PERIPHERY OF THE LARGE TROPICAL RIDGE...CONCENTRATING INTO A 600 NM WIDE TROPICAL PLUME STREAMING ACROSS NORTHERN OLD MEXICO AND THE GULF OF MEXICO... EVENTUALLY FEEDING INTO THE CONVECTION AHEAD OF A SHORTWAVE TROUGH ADVANCING ACROSS THE SE CONUS. LOW LEVELS...A SURFACE RIDGE EXTENDS SE ACROSS THE AREA FROM 32N138W TO TO 16N106W. ANTICYCLONIC WINDS AT 10-15 KT ARE OBSERVED ACROSS THE SUB-TROPICS WITH SEAS 7-10 FT IN MIXING N...NE...AND NW SWELL. S OF THE SURFACE RIDGE...GENERALLY TO THE W OF LINE FROM 22N110W TO 10N122W TO 08N140W...N TO NE TRADES CONTINUE AT 15-25 KT WITH SEAS 8-11 FT IN MIXED NE AND NW SWELL. A WEAK COLD FRONT IS PASSING E ACROSS THE N-CENTRAL WATERS NE OF THE RIDGE ACCOMPANIED BY ONLY A 10-15 KT SW-W-NW WIND SHIFT. EXPECT THE FRONT TO WEAKEN FURTHER AS IT REACHES THE NORTHERN BAJA PENINSULA ON SUN...AND PASS THROUGH THE GULF OF CALIFORNIA SUN NIGHT. A SURFACE HIGH WILL SHIFT SE TO NEAR 30N132W LATE SAT WITH THIS POST FRONTAL HIGH PRESSURE INCREASING THE NORTHERLY FLOW TO 15-20 KT WELL W OF THE FRONT WITH ANOTHER ROUND OF NW SWELL DRIVING THE COMBINED SEAS UP TO 10-13 FT ACROSS THE N-CENTRAL WATERS ON SUN...WITH 8-10 FT SEAS REACHING THE NORTHERN BAJA PENINSULA ON SUN EVENING...THEN SUBSIDING TO 5-7 FT BY LATE MON. AS THE SURFACE HIGH SHIFTS S INTO THE AREA THE NE TRADES WILL CONTINUE TO PULSE AT 20-25 KT ACROSS THE TROPICS FROM 07-22N W OF 130W. LARGE LONG PERIOD NW SWELL WILL PROPAGATE INTO THE FAR NW PACIFIC WATERS LATE SUN NIGHT DRIVING SEAS UP TO 13 FT. THESE NW SWELLS WILL CONTINUE EASTWARD GRADUALLY SUBSIDING WITH SEAS OF 7-10 FT REACHING THE NORTHERN BAJA PENINSULA LATE TUE NIGHT...AND REACHING THE SOUTHERN BAJA PENINSULA LATE WED NIGHT. GULF OF TEHUANTEPEC...A COLD FRONT IS CURRENTLY PROGRESSING S ACROSS THE NW BAY OF CAMPECHE. EXPECT THE ASSOCIATED N WINDS TO BEGIN TO SURGE THROUGH THE CHIVELA PASS INTO THE GULF OF TEHUANTEPEC JUST AFTER SUNRISE THIS MORNING. THESE N WINDS WILL RAPIDLY BUILD TO GALE FORCE THIS AFTERNOON...WITH NEAR STORM CONDITIONS...SEAS TO 17 FT...EXPECTED TONIGHT TILL JUST AFTER SUNRISE ON SUN. GUIDANCE SUGGESTS GALE CONDITIONS WILL END JUST AFTER SUNRISE ON MON...WITH THE NORTHERLY WINDS DIMINISHING BELOW 20 KT LATE MON. GULF OF PAPAGAYO...NE-E 15-25 KT SURGES ARE EXPECTED TO CONTINUE AND GRADUALLY SPREAD AS FAR W AS 94W ON SUN WHERE THE ASSOCIATED NE SWELLS WILL THEN MIX WITH SW CROSS EQUATORIAL SWELL AS WELL AS N SWELL PROPAGATING S FROM THE STRONG TEHUANTEPEC EVENT. $$ NELSON