000 AXPZ20 KNHC 280334 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SAT NOV 28 2015 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0300 UTC. ...SPECIAL FEATURES... NEWLY DOWNGRADED TROPICAL STORM SANDRA IS CENTERED NEAR 21.3N 108.7W AT 0300 UTC...OR ABOUT 120 NM W OF LAS ISLAS TRES MARIAS MEXICO AND 115 NM S-SE OF THE SOUTHERN TIP OF BAJA MEXICO... MOVING N OR 05 DEG AT 9 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 990 MB. MAXIMUM SUSTAINED WIND SPEED HAS DECREASED TO 55 KT WITH GUSTS TO 65 KT. STRONG SOUTHWESTERLY UPPER LEVEL WIND SHEAR CONTINUES TO IMPACT SANDRA...AND HAS DISPLACED THE ASSOCIATED THUNDERSTORMS WELL TO THE E AND NE OF THE SURFACE CENTER. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS OCCURRING FROM 90 TO 360 NM ACROSS THE E SEMICIRCLE. SANDRA IS EXPECTED TO CONTINUE TO WEAKEN QUICKLY THROUGH SATURDAY AS THE HOSTILE UPPER LEVEL WIND SHEAR IS FORECAST TO INCREASE...WITH THE EXPOSED LOW LEVEL CENTER EXPECTED TO MOVE ASHORE ALONG THE COAST OF SINALOA MEXICO SATURDAY AFTERNOON AS A TROPICAL DEPRESSION OR POSSIBLY A REMNANT LOW. DETERIORATING MARINE CONDITIONS SHOULD BE EXPECTED ACROSS THE SOUTH HALF OF THE GULF OF CALIFORNIA TONIGHT AND SATURDAY AS SOUTHERLY SWELL GENERATED BY SANDRA MOVES INTO THE LOWER TWO-THIRDS OF THE GULF...AND COMBINES WITH THE TROPICAL STORM FORCE WINDS OF SANDRA. BANDS AND CLUSTERS OF SHOWERS AND THUNDERSTORMS WILL ALSO IMPACT THE MEXICAN COASTAL STATES FROM JALISCO TO SINALOA..AND SPREADING INLAND ALONG THE WESTERN SLOPES OF THE SIERRA MADRE OCCIDENTALES THROUGH LATE SATURDAY. THIS WILL PRODUCE THE POTENTIAL FOR FLASH FLOODING AND LANDSLIDES. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP2/WTPZ22 NHC FOR MORE DETAILS. GULF OF TEHUANTEPEC...STRONG HIGH PRESSURE ACROSS THE EASTERN SEABOARD OF THE U.S. WILL SHIFT SLIGHTLY SW THROUGH SATURDAY AND FORCE THE STRONG E-NE WIND FLOW CURRENTLY ACROSS THE SOUTHEAST GULF OF MEXICO AND NW CARIBBEAN TO BECOME MORE NORTHEASTERLY TONIGHT AND SATURDAY. THIS WILL ALLOW THE GAP WIND FLOW ACROSS CENTRAL AMERICA TO INCREASE ACROSS THE EASTERN PACIFIC COASTAL ZONES OF CENTRAL AMERICA TONIGHT THROUGH THE WEEKEND. NORTHERLY WINDS OF 20-30 KT ACROSS THE GULF OF TEHUANTEPEC LATE THIS EVENING ARE EXPECTED TO STRENGTHEN TONIGHT TO MINIMAL GALE FORCE DURING THE LATE NIGHT AND EARLY MORNING HOURS...AND SLOWLY DIMINISH TO AROUND 30 KT BY LATE SATURDAY MORNING...BEFORE INCREASING TO GALE FORCE AGAIN SATURDAY NIGHT THROUGH SUNDAY MORNING...AND LIKELY AGAIN SUNDAY NIGHT THROUGH MONDAY MORNING. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM LOW PRES 1005 MB NEAR 07.5N74W TO 05N81.5W TO 07N94W...WHERE IT REMAINS FRACTURED...THEN RESUMES NEAR 17N110W TO 07N118W TO 06N123W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON 03.5N131W TO BEYOND 03N140W. NO SIGNIFICANT CONVECTION. ...DISCUSSION... A COLD FRONTAL BOUNDARY THAT MOVED THROUGH BAJA CALIFORNIA AND MOST OF THE EASTERN WATERS THE PAST FEW DAYS HAS MERGED ACROSS CENTRAL PORTIONS ALONG ABOUT 18N WITH THE REMNANTS OF FORMER TROPICAL CYCLONE RICK. A STRONG PRESSURE GRADIENT BETWEEN HIGH PRESSURE TO THE NORTH AND THIS MERGED FEATURES IS SUPPORTING A BROAD BAND OF FRESH TO STRONG NE WINDS FROM GENERALLY 18N TO 24N BETWEEN 120W AND 132W AND FROM 15N TO 24N W OF 132W...WITH COMBINED SEAS OF 8 TO 14 FT PREVAILING IN MIXED NW SWELL AND NE WIND WAVES. ELSEWHERE THIS LONG PERIOD NW SWELL IS MIXING WITH NE WIND WAVES AND SE SWELL FROM SANDRA... RESULTING IN CONFUSED SEAS OF 8 TO 11 FT GENERALLY FROM 12N TO 26N BETWEEN 112W AND 125W. THE AREA OF FRESH TO STRONG TRADES IS EXPECTED TO SHIFT WEST-SOUTHWESTWARD AS RIDGING BUILDS SOUTHEASTWARD ACROSS THE NORTHERN FORECAST WATERS THROUGH SUN. BY SUN AS THE AREA OF TRADES WEAKENS AND SHRINKS IN AREAL COVERAGE...WHILE 8 TO 11 FT COMBINED SEAS ARE FORECAST TO PREVAIL W OF LINE FROM 06N125W TO 18N116W TO 25N133W TO 30N133W. GAP WINDS... AS MENTIONED ABOVE...THE GAP WIND FLOW ACROSS CENTRAL AMERICA AND INTO THE EASTERN PACIFIC IS EXPECTED TO INCREASE TONIGHT THROUGH THE WEEKEND AS HIGH PRESSURE BUILDS ACROSS THE GULF OF MEXICO AND THE NW CARIBBEAN...AS WINDS THERE TURN MORE NORTHEASTERLY. THIS NORTHEAST DIRECTION WILL AID IN PRODUCING STRONGER WINDS BLOWING ACROSS AND DOWNSTREAM OF THE GULF OF PAPAGAYO FOR THE NEXT FEW DAYS...AND WILL ALSO RESULT IN NORTHERLY WINDS AROUND 20 KT SPILLING ACROSS PANAMA AND ACROSS THE GULF OF PANAMA TONIGHT THROUGH THE WEEKEND. LOOK FOR OTHER GAP WIND PRONE AREAS SUCH AS THE GULF OF FONSECA TO ALSO REACH NEAR 20 KT EACH NIGHT AND EARLY MORNING THROUGH MONDAY. $$ STRIPLING