000
AXPZ20 KNHC 261707 AAA
TWDEP 

TROPICAL WEATHER DISCUSSION...AMENDED                          
NWS NATIONAL HURRICANE CENTER MIAMI FL  
1605 UTC THU NOV 26 2015

...UPDATED FOR HURRICANE SANDRA...

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1545 UTC.               

...SPECIAL FEATURES...

AT 1500 UTC HURRICANE SANDRA WAS CENTERED NEAR 15.7N 110.1W...OR
ABOUT 495 MILES S OF THE SOUTHERN TIP OF THE BAJA CALIFORNIA
PENINSULA. SANDRA IS MOVING N OR 005 DEGREES AT 10 KT WITH A
TURN TOWARDS THE NE EXPECTED. THE ESTIMATED MINIMUM CENTRAL
PRESSURE WAS 947 MB. ALTHOUGH SANDRA IS BEGINNING TO SHOW A
WEAKENING TREND SHE IS STILL A CATEGORY 4 HURRICANE WITH MAXIMUM
SUSTAINED WINDS OF 115 KT WITH GUSTS TO 140 KT. SANDRA IS
FORECAST TO ENCOUNTER STRONG SOUTHWESTERLY WIND SHEAR AND IS
EXPECTED TO RAPIDLY WEAKEN TO A TROPICAL STORM ON FRI AND A
REMNANT LOW ON SAT. CURRENTLY NUMEROUS STRONG CONVECTION IS
OBSERVED WITHIN 240 NM NE...AND WITHIN 120 NM SE QUADRANTS OF
CENTER. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED
ELSEWHERE WITHIN 330 NM N AND WITHIN 150 NM S SEMICIRCLES.
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 WILL SOON
MOVE ONSHORE THE PACIFIC COAST OF MAINLAND MEXICO BETWEEN 18-24N
RESULTING IN LARGE RAINFALL ACCUMULATIONS THAT MAY CAUSE LIFE
THREATENING FLASH FLOODS AND LANDSLIDES. LARGE SWELLS WILL BEGIN
TO REACH THE PACIFIC COAST OF MAINLAND MEXICO...AND 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...            

A 1008 MB SURFACE LOW IS MEANDERING ALONG THE CARIBBEAN COAST OF
COLOMBIA AT 09N77W. THE MONSOON TROUGH EXTENDS SW FROM THIS LOW
ACROSS TROPICAL EPAC TO NEAR 04N90W...THEN TURNS NW TO 07N104W
WHERE IT LOSES IDENTITY IN THE BROAD CYCLONIC CIRCULATION
ASSOCIATED WITH TROPICAL CYCLONE SANDRA. THE MONSOON TROUGH
RESUMES SW OF SANDRA AT 12N112W...AND CONTINUES SW TO 05N120W
WHERE SCATTEROMETER WINDS INDICATE A TRANSITION TO AN ITCZ. THE
ITCZ THEN CONTINUES WSW TO BEYOND 02N140W. ISOLATED MODERATE TO
STRONG CONVECTION IS NOTED ALONG THE EASTERN SEGMENT OF THE
MONSOON TROUGH WITHIN 90 NM EITHER SIDE OF A LINE FROM 06N79W TO
03N90W TO 10N103W. SIMILAR CONVECTION IS NOTED ALONG THE WESTERN
SEGMENT OF THE MONSOON TROUGH...ROUGHLY WITHIN 60 NM EITHER SIDE
OF A LINE FROM 11N109W TO 05N116W TO 06N123W.  

...DISCUSSION...

A WEAKENING COLD FRONT EXTENDS SW FROM 30N111W ACROSS THE GULF
OF CALIFORNIA TO THE PACIFIC COAST OF THE BAJA PENINSULA AT
27N114W TO 24N124W TO 26N134W. THE REMNANT TROUGH OF TROPICAL
CYCLONE RICK IS ANALYZED FROM 17.5N128.5W TO 22N124.5W. THE
STRONG GRADIENT BETWEEN THE FRONT AND THE TROUGH IS SUPPORTING A
BAND OF STRONG NE 20-25 KT WINDS WITHIN 90 NM EITHER SIDE OF A
LINE FROM 19N131W TO 26N123W WITH COMBINED SEAS OF 8-10 FT. LONG
PERIOD NW SWELL IS MIXING WITH LONG PERIOD SE SWELL...RESULTING
IN COMBINED SEAS 8-14 FT TO THE N OF A LINE FROM 30N116W TO
19N130W TO 26N140W WINDS 20 KT OR LESS. THE HIGHEST SEAS WERE
MEASURED BY AN ALTIMETER PASS NEAR 30N128W. ALTHOUGH THE COLD
FRONT AND TROUGH SHOULD DISSIPATE TONIGHT...THE 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 9-12 FT SEAS.
THE ARES WILL BE SURROUNDED BY 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 LONG
PERIOD SE AND NW SWELL WILL 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 FLOW DIMINISHED
BELOW GALE FORCE THIS MORNING BUT EXPECT N-NE SURGES OF 20-30 KT
ACROSS THE GULF WATERS TO AS FAR S AS 13N97W THROUGH TONIGHT.
EXPECT A MAXIMUM OF 25 KT ON SAT MORNING...THEN GUIDANCE
SUGGESTS STRONGER DRAINAGE FLOW OF 30 KT LATE SAT NIGHT INTO SUN
MORNING WITH MINIMAL GALE FORCE CONDITIONS DEVELOPING ON SUN
NIGHT INTO MON.   

GULF OF PAPAGAYO...A TIGHT PRESSURE GRADIENT WILL CONTINUE TO
SUPPORT PULSES OF NE-E 20-25 KT WINDS TONIGHT AND AGAIN ON FRI
NIGHT WITH SEAS BUILDING TO 7 FT DOWNSTREAM OF THE GULF OF
PAPAGAYO TO NEAR 09N90W. GUIDANCE SUGGESTS A SLIGHTLY STRONGER
EVENT ON SAT NIGHT.
 
$$
NELSON