000 AXPZ20 KNHC 270350 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC FRI NOV 27 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... AT 0300 UTC...HURRICANE SANDRA WAS CENTERED NEAR 18.0N 109.7W...OR ABOUT 300 NM S OF THE SOUTHERN TIP OF THE BAJA CALIFORNIA PENINSULA. SANDRA IS MOVING N OR 010 DEGREES AT 11 KT WITH A GRADUAL VEERING TOWARDS THE N-NE EXPECTED ON FRIDAY. ESTIMATED MINIMUM CENTRAL PRESSURE WAS 956 MB. SOUTH WESTERLY UPPER LEVEL WIND SHEAR IMPACTING SANDRA THIS AFTERNOON APPEARS TO HAVE DIMINISHED SLIGHTLY THIS EVENING...AND AN 8 NM WIDE EYE OF SANDRA HAS BECOME CLEARLY EVIDENT IN SATELLITE PHOTOS TONIGHT. MAXIMUM SUSTAINED WINDS REMAIN 105 KT WITH GUSTS 130 KT...A CATEGORY THREE HURRICANE. NUMEROUS STRONG CONVECTION WAS OCCURRING WITHIN 90 NM ACROSS THE N AND 120 NM S SEMICIRCLES... WHILE SCATTERED MODERATE TO STRONG CONVECTION WAS ELSEWHERE WITHIN 360 NM NE AND 150 NM SW SEMICIRCLES. AS SANDRA CONTINUES N AND THEN N-NE TONIGHT AND FRIDAY...THE UPPER LEVEL WIND SHEAR IS EXPECTED TO INCREASE ACROSS THE SYSTEM...AND A FAIRLY QUICK WEAKENING TREND IS EXPECTED...WITH SANDRA REACHING TROPICAL STORM STRENGTH ON FRI NIGHT AS IT APPROACHES THE SOUTHERN TIP OF BAJA CALIFORNIA. INTERESTS IN THE SOUTHERN PORTIONS OF THE BAJA PENINSULA AS WELL ALONG THE CENTRAL PACIFIC COAST OF MEXICO SHOULD MONITOR THE PROGRESS OF SANDRA. CLUSTERS OF STRONG THUNDERSTORMS HAVE BEGUN TO MOVE ONSHORE ACROSS THE PACIFIC COAST OF MAINLAND MEXICO BETWEEN 18-22N...RESULTING IN HEAVY RAINFALL. OCCASIONAL BANDS AND CLUSTERS OF THUNDERSTORMS WILL AFFECT THE W COASTAL STATES OF MEXICO FROM MICHOACAN TO SINALOA DURING THE NEXT 48 HOURS AND COULD PRODUCE LARGE RAINFALL ACCUMULATIONS THAT MAY CAUSE LIFE THREATENING FLASH FLOODS AND LANDSLIDES. LARGE SWELLS HAVE BEGUN TO REACH THE PACIFIC COAST OF MAINLAND MEXICO...AND WILL SPREAD NORTH TO THE SOUTHERN PORTION OF THE BAJA PENINSULA TONIGHT AND FRI. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP2/WTPZ22 KNHC FOR MORE DETAILS. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM LOW PRESSURE 1006 MB NEAR 09.5N74.5W TO 04.5N86W TO 05N92W...WHERE IT IS FRACTURED...THEN RESUMES NEAR 12N111W TO 04N125W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON TO BEYOND 02N140W. NO SIGNIFICANT CONVECTION. ...DISCUSSION... A WEAKENING COLD FRONT EXTENDS SW FROM 28N110W ACROSS THE GULF OF CALIFORNIA TO 24.5N112W TO 21N130W. A TROUGH ORIGINATING FROM THE REMNANTS OF TROPICAL CYCLONE RICK IS LOCATED FROM 16N132W TO 20N124W. THE STRONG PRESSURE GRADIENT BETWEEN HIGH PRESSURE BEHIND THE FRONT AND THE TROUGH IS SUPPORTING A BAND OF STRONG NE 20-25 KT WINDS WITHIN 360 NM NW OF THE FRONT AND TROUGH BETWEEN 120W AND 134W WITH COMBINED SEAS OF 8-15 FT IN NW SWELL. ELSEWHERE THIS LONG PERIOD NW SWELL IS MIXING WITH NE WIND WAVES AND SE SWELL FROM SANDRA...RESULTING IN COMBINED SEAS 8-10 FT TO THE N OF LINE FROM 30N118W TO 26N115W TO 17N132W TO 22N140W. ALTHOUGH THE COLD FRONT AND TROUGH SHOULD DISSIPATE ON FRIDAY...THE PRESSURE GRADIENT WILL INCREASE WITH AN AREA OF NE- E 20-25 KT ACROSS THE TROPICAL WATERS FROM 16-23N BETWEEN 123- 140W ON FRI...WITH 9-13 FT SEAS PREVAILING...WITH SEAS OF 8-10 FT ACROSS THE WATERS N OF 13N W OF 115W. BY SAT THE AREA OF ENHANCED NE TRADES WILL SHIFT W TO WITHIN THE AREA FROM 15-19N BETWEEN 128-140W. THE NW SWELL WILL CONTINUE TO MERGE WITH THE MIXED SWELL FROM TROPICAL CYCLONE SANDRA...RESULTING IN COMBINED SEAS OF 7-11 FT WITHIN AN AREA BOUNDED BY LINE FROM 30N140W TO 25N130W TO 29N115W TO 13N115W TO 10N140W TO 30N140W. GAP WINDS...GULF OF TEHUANTEPEC...THE NORTHERLY WIND FLOW ACROSS AND DOWNSTREAM OF THE GULF HAS DIMINISHED TO 20-25 KT THIS AFTERNOON...WITH MAXIMUM SEAS TO 9 FT. EXPECT N-NE SURGES OF 20- 30 KT ACROSS THE GULF WATERS TO AS FAR S AS 13N97W THROUGH TONIGHT...THEN DECREASING TO 20-25 BY FRIDAY AFTERNOON. COMPUTER MODEL GUIDANCE SUGGESTS STRONGER DRAINAGE FLOW OF 30 KT LATE SAT NIGHT INTO SUN MORNING WITH MINIMAL GALE FORCE CONDITIONS POTENTIALLY DEVELOPING ON SUN NIGHT INTO MON. GULF OF PAPAGAYO...A TIGHT PRESSURE GRADIENT ACROSS THE W AND SW CARIBBEAN WILL CONTINUE TO SUPPORT PULSES OF NE TO E 20-25 KT WINDS TONIGHT AND AGAIN ON FRI NIGHT ACROSS THE PAPAGAYO REGION AND DOWNSTREAM TO AROUND 90W...WITH SEAS BUILDING TO 7-8 FT DOWNSTREAM TO NEAR 09N90W. COMPUTER MODEL GUIDANCE SUGGESTS A SLIGHTLY STRONGER EVENT ON SAT NIGHT. $$ STRIPLING