000 AXPZ20 KNHC 170925 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC SAT DEC 17 2011 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 0700 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM 09N84W TO 06N100W. ITCZ AXIS EXTENDS FROM 06N100W TO 10N116W TO 07N125W TO BEYOND 07N140W. SCATTERED MODERATE WITH ISOLATED STRONG CONVECTION LIES WITHIN 150 NM N AND 120 NM S OF THE AXIS W OF 132W. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM EITHER SIDE OF THE AXIS BETWEEN 114W AND 125W. ...DISCUSSION... AN UPPER CYCLONE OVER FAR SW CALIFORNIA AND FAR NW MEXICO WILL BE SLOW TO MOVE UNTIL SUN WHEN IT BEGINS TO PASS EASTWARD INTO ARIZONA. AN ASSOCIATED 1016 MB LOW PRES SYSTEM LIES NEAR 29N116W AND EXTENDS A FRONTAL TROUGH S FROM THE LOW TO 26N116W TO 24N120W. THIS TROUGH WILL DISSIPATE TODAY WITH THE WEAKENING LOW LINGERING OFFSHORE UNTIL EVENING. SHOWERS ASSOCIATED WITH THE CYCLONE WILL PRIMARILY IMPACT THE FORECAST AREA OVER THE NORTHERN GULF OF CALIFORNIA...BAJA CALIFORNIA NORTE AND SONORA. SHIPS DGHJ AND V7NV4 REPORTED FRESH NE WINDS WITH SEAS TO 9 FT BEHIND THE FRONTAL TROUGH OVER N CENTRAL WATERS AT 0600 UTC. THESE WINDS ARE EXPECTED TO DIMINISH TODAY AS THE FRONTAL TROUGH AT THE SURFACE DISSIPATES. A DISSIPATING COLD FRONT ASSOCIATED WITH A WEAKENING DEEP LAYER TROUGH WILL APPROACH NW WATERS TODAY AND USHER IN A NEW ROUND OF NW SWELL...WITH SEAS REACHING 10-12 FEET OVERNIGHT TONIGHT GENERALLY IN THE AREA N OF 20N W OF 130W. THE FRONT HAS ALREADY WEAKENED THE SUBTROPICAL HIGH PRES OVER NW WATERS AND CAUSED THE TRADE WINDS TO SHRINK WEST OF 130W ACCORDING TO THE 0616 UTC ASCAT PASS. NEW HIGH PRES MOVING IN BEHIND THE FRONT WILL MERGE ON SUN WITH THE HIGH PRES CURRENTLY IN PLACE...ALLOWING TRADES TO EXPAND EASTWARD TO 113W THROUGH MON MORNING. MOISTURE IS POOLED ALONG THE ITCZ/MONSOON TROUGH AXIS WITH PRECIPITABLE WATER VALUES HIGHEST ALONG THE EASTERN EDGE OF THE AXIS INTO THE SW CARIBBEAN AS WELL AS ON THE FAR W EDGE OF THE FORECAST AREA NEAR 140W. DIFFLUENCE ALONG AN UPPER RIDGE AXIS OVER THE SW CARIBBEAN IS OCCUPYING THE MOISTURE NEAR PANAMA AND COSTA RICA...WITH PRECIPITATION CURRENTLY E OF THE AREA OVER THE SW CARIBBEAN. MEANWHILE...UPPER DIFFLUENCE ASSOCIATED WITH THE REAR RIGHT QUADRANT OF A 60-80 KT UPPER JET LIES OVER WESTERN WATERS OVER THE ITCZ. THIS DIFFLUENCE IS ENHANCING THE CONVECTION IN FAR W WATERS DESCRIBED IN THE ITCZ/MONSOON TROUGH SECTION ABOVE. THE JET IS EXPECTED TO SHIFT NORTHEASTWARD AWAY FROM THE ITCZ AXIS OVER THE NEXT FEW DAYS...WITH PRECIPITATION CHANCES EXPECTED TO DIMINISH. GAP WINDS... GULF OF TEHUANTEPEC...THE FORECAST GUIDANCE AGREES ON BRINGING N TO NE WINDS TO GALE FORCE IN THE GULF OF TEHUANTEPEC THIS EVENING. WHILE THERE IS NO STRONG...PROGRESSIVE COLD FRONT EXPECTED TO SWEEP THROUGH THE GULF OF MEXICO TO INCREASE WINDS THROUGH THE ISTHMUS OF TEHUANTEPEC...THE BUILDING PRES GRADIENT BETWEEN HIGH PRES PASSING SE OVER THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY AND LOWER PRES ALONG THE MONSOON TROUGH TO THE S WILL BE ENOUGH TO INITIATE GALE FORCE WINDS. WINDS WILL DIMINISH BELOW GALE FORCE OVERNIGHT SUN NIGHT AS THE HIGH PRES SHIFTS EASTWARD. FRESH TO STRONG N WINDS ARE BELIEVED TO HAVE ALREADY BEGUN IN THE GULF...WITH THE OBSERVATION STATION AT SALINA CRUZ REPORTING 15 KT N WINDS AT 0000 UTC. GULF OF PAPAGAYO...THE BUILDING PRES GRADIENT OVER SOUTHERN MEXICO HAS EXTENDED S TO THE GULF OF PAPAGAYO. SHIP PHSG REPORTED 23 KT NE WINDS AT 10N87W AT 0500 UTC AND THE 0250 UTC ASCAT PASS SHOWED 20 KT WINDS WITHIN 150 NM DOWNWIND OF PAPAGAYO. THESE WINDS WILL REMAIN STRONG THROUGH SUN AND BEGIN TO DIMINISH OVERNIGHT SUN NIGHT AS HIGH PRES TO THE N SHIFTS EASTWARD. $$ SCHAUER