000
AXNT20 KNHC 182342
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST SUN DEC 18 2011

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL 
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF 
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE 
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE 
IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL 
ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2330 UTC.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH REMAINS INLAND ACROSS AFRICA. THE ITCZ 
EXTENDS WESTWARD FROM THE SOUTHERN COAST OF GUINEA NEAR 9N13W 
ALONG 6N20W 4N30W 4N40W TO 3N47W. SCATTERED WEAK CONVECTION IS 
FROM 5N-11N BETWEEN 32W-50W AND WITHIN 50 NM ON EITHER SIDE OF 
THE AXIS BETWEEN 20W-32W. 

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE OF HIGH PRESSURE COVERS MUCH OF THE BASIN 
THIS EVENING...SUPPRESSING DEEP CONVECTION ACROSS THE AREA 
EXCEPT FOR A FEW CLUSTERS OF SCATTERED SHOWERS REMAINING ACROSS 
THE STRAITS OF FLORIDA...OVER THE SOUTHERN HALF OF THE BASIN S 
OF 24N...AND THE FAR WRN WATERS NEAR THE COAST OF MEXICO AND 
TEXAS N OF 21N W OF 96W. A WEAK SURFACE TROUGH IS ANALYZED IN 
THIS REGION FROM 26N97W TO 22N96W. ENE WINDS 10-15 KT ARE 
OBSERVED ACROSS THE AREA. SOUTHERLY RETURN FLOW IS EXPECTED TO 
RE-ESTABLISH OVER PORTIONS OF THE WESTERN GULF ON MONDAY...AS AN 
AREA OF LOW PRESSURE DEVELOPS OVER NORTH TEXAS AND OKLAHOMA. THE 
NEXT COLD FRONT IS THEN FORECAST TO ENTER THE NW GULF WATERS 
EARLY TUESDAY.

CARIBBEAN SEA...
SCATTERED SHOWERS AND THUNDERSTORMS ARE OVER THE SW CARIBBEAN 
DUE TO MONSOONAL FLOW AROUND THE AXIS ANALYZED INLAND ACROSS 
CENTRAL AMERICA. THE ACTIVITY IS AFFECTING MOSTLY THE COASTAL 
WATERS OF PANAMA...COSTA RICA...AND NICARAGUA S OF 14N W OF 77W. 
AN UPPER LEVEL ANTICYCLONE IS NOTICED IN THE THE UPPER LEVEL 
CLOUD FIELD W OF 72W...PROVIDING DIFFLUENCE ALOFT OVER THE SW 
CARIBBEAN HELPING PRODUCE THE CONVECTION AROUND THE MONSOON 
TROF. THE REMAINDER OF THE CARIBBEAN UNDER A GENTLE TO MODERATE 
NE TRADES THIS EVENING. CLUSTERS OF SCATTERED SHOWERS AND 
POSSIBLE ISOLATED THUNDERSTORMS ARE EMBEDDED IN THE FLOW. 
COMPUTER MODELS SUGGEST AN INCREASE IN PRECIPITATION AND WINDS 
OVER MOST OF THE CENTRAL...WESTERN AND NW CARIBBEAN OVER THE 
NEXT 24-36 HOURS.

ATLANTIC OCEAN...
AN UPPER LEVEL LONGWAVE TROUGH IS PROGRESSING OVER THE WRN ATLC 
AND SUPPORTS A COLD FRONT ANALYZED INTO THE DISCUSSION AREA 
ALONG NEAR 32N65W EXTENDING SW TO THE CENTRAL BAHAMAS NEAR 
24N78W. POSSIBLE ISOLATED SHOWERS ARE OCCURRING WITHIN 70 NM 
EITHER SIDE OF THE FRONT. GALE FORCE WINDS ARE WITHIN 150 NM ON 
EITHER SIDE OF THE FRONT N OF 27N...GENERATING SEAS BETWEEN 9 TO 
15 FEET. A NARROW UPPER LEVEL TROUGH IS WELL TO THE E OF THE 
FRONT SUPPORTING A WEAK 1009 MB LOW NEAR 27N50W. A DISSIPATING 
STATIONARY FRONT REMAINS DETACHED FROM THE LOW CENTER EXTENDING 
FROM 27N46W TO 20N47W TO 17N48W THEN AS SURFACE TROUGH TO 
14N50W. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 240 NM 
EAST OF THE BOUNDARY N OF 22N AND S OF 18N. CLOSER TO THE LOW 
CENTER...A WEAKENING STATIONARY FRONT EXTENDS NORTHWARD FROM THE 
LOW CENTER TO BEYOND 32N50W AND A SURFACE TROUGH IS ANALYZED 
FROM THE LOW TO 23N51W WITHOUT ANY SIGNIFICANT CONVECTION. THE 
REMAINDER OF THE ERN ATLC IS EXPERIENCING MOSTLY FAIR WEATHER 
DUE TO SURFACE RIDGING AROUND A 1033 MB HIGH S OF THE AZORES 
NEAR 37N27W. AS THE WRN ATLC COLD FRONT MOVES EASTWARD...EXPECT 
THE LOW PRESSURE SYSTEM IN THE CENTRAL ATLC TO DISSIPATE OVER 
THE NEXT DAY OR SO.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$

GARCIA