000
AXNT20 KNHC 151742
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST SAT DEC 15 2012

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1715 UTC.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS ACROSS AFRICA TO THE COAST OF 
LIBERIA. THE ITCZ CONTINUES FROM THE COAST OF LIBERIA TO 4N30W 
TO NORTHERN SOUTH AMERICA NEAR 2N51W. SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION IS FROM 2N TO 6N BETWEEN 35W-47W. 
SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 120 NM S OF 
ITCZ AXIS BETWEEN 20W AND 26W.
 
...DISCUSSION...

GULF OF MEXICO...
A BROAD UPPER RIDGE EXTENDS FROM THE EPAC WATERS ACROSS SE 
MEXICO AND THE BAY OF CAMPECHE THROUGH THE GULF OF MEXICO AND 
THE SE CONUS. STRONG SW TO W FLOW ON THE NORTHERN PERIPHERY OF 
THE RIDGE IS BRINGING ABUNDANT MID/UPPER LEVEL MOISTURE INTO THE 
GULF REGION. A SURFACE RIDGE COVERS THE GULF ANCHORED BY A 1026 
MB HIGH PRES LOCATED OVER THE MIDDLE ATLANTIC STATES. SOUTHERLY 
RETURN FLOW IS ON INCREASE ACROSS THE WESTERN GULF AHEAD OF THE 
NEXT COLD FRONT FORECAST TO ENTER THE GULF WATERS SUN NIGHT INTO 
MON MORNING. THE COLD FRONT WILL REACH FROM NEAR SE LOUISIANA TO 
THE SW GULF OF MEXICO EARLY MON. SCATTEROMETER DATA ALONG WITH 
SURFACE OBSERVATIONS SHOW SLY WINDS OF 15-20 KT OVER THE WESTERN 
GULF WHILE A GENTLE TO MODERATE E-SE BREEZE IS NOTED ACROSS THE 
REMAINDER OF THE AREA. THE RETURN FLOW IS FORECAST TO CONTINUE 
SPREADING EASTWARD THROUGH THE REST OF THE WEEKEND AS THE HIGH 
OVER THE CONUS SLIDES EAST INTO THE NORTH ATLC. SCATTERED 
SHOWERS AND LIKELY ISOLATED TSTMS ARE OBSERVED OVER THE NW GULF. 
SOME STRATOCUMULUS CLOUDS ARE STILL SEEN ON VISIBLE SATELLITE 
PICTURES ACROSS THE EASTERN GULF.  

CARIBBEAN SEA...
A RIDGE/TROUGH PATTERN COVERS THE BASIN. THE AFOREMENTIONED 
BROAD UPPER RIDGE ALSO DOMINATES WESTERN CUBA AND THE WESTERN 
CARIBBEAN. A MIDDLE/UPPER LEVEL TROUGH OVER THE ATLANTIC OCEAN 
ENTERS THE CARIBBEAN SEA TROUGH HISPANIOLA THEN CONTINUES SW TO 
NEAR 11N76W. STRONG SUBSIDENCE AND IMPLIED DRY AIR MASS PREVAILS 
IN THE MIDDLE AND UPPER LEVELS OF THE ATMOSPHERE OVER THE 
MAJORITY OF THE CARIBBEAN SEA. HOWEVER...SOME CLOUDINESS WITH 
EMBEDDED SHOWERS AND ISOLATED TSTMS ARE SEEN MAINLY SOUTH OF 
DOMINICAN REPUBLIC. THIS CONVECTIVE ACTIVITY IS ASSOCIATED WITH 
A TROUGH ANALYZED ON THE 1200 UTC SURFACE MAP FROM THE MONA 
PASSAGE TO NEAR ARUBA IN THE ABC ISLANDS. UPPER DIFFLUENCE AHEAD 
OF THE UPPER TROUGH IS ALSO HELPING TO MAINTAIN THIS ACTIVITY 
WHICH CAN BE SEEN ON THE SAN JUAN DOPPLER RADAR. SHALLOW 
MOISTURE EMBEDDED IN THE TRADE WIND FLOW WILL MOVE ACROSS THE 
REGION PRODUCING ISOLATED TO SCATTERED PASSING SHOWERS. A RATHER 
WEAK PRES GRADIENT WILL PREVAIL ACROSS THE BASIN DURING THE NEXT 
SEVERAL DAYS PRODUCING GENTLE TO MODERATE TRADEWINDS INTO EARLY 
WED.   

ATLANTIC OCEAN...
IN THE WESTERN ATLANTIC A MID/UPPER LEVEL TROUGH CROSSES E OF 
BERMUDAS NEAR 32N60W THEN CONTINUES SW THROUGH HISPANIOLA INTO 
THE CARIBBEAN SEA. THIS TROUGH SUPPORTS A WEAK COLD FRONT THAT 
EXTENDS FROM 31N57W TO 25N67W WHERE IT BECOMES STATIONARY TO  
THE CENTRAL BAHAMA ISLANDS NEAR 24N75W. A NARROW BAND OF CLOUDS 
WITH ISOLATED SHOWERS IS ASSOCIATED WITH THE FRONT. A WEAK 
SURFACE TROUGH PERSISTS JUST E OF FLORIDA AND EXTENDS ALONG 80W 
FROM 27N TO 31N. DOPPLER RADAR REVEALS SOME SHOWER ACTIVITY NEAR 
THE TROUGH AXIS AND JUST OFF THE COAST OF GEORGIA. A SURFACE 
RIDGE CONTINUES TO BUILD IN THE WAKE OF THE FRONT AND CURRENTLY 
DOMINATES THE SW N ATLANTIC AND THE SE CONUS...INCLUDING THE 
STATE OF FLORIDA. GUSTY NE-E WINDS ON THE SOUTHERN PERIPHERY OF 
THE RIDGE ARE BRINGING PATCHES OF MOISTURE WITH EMBEDDED SHOWERS 
TO SOUTH FLORIDA...AFFECTING MAINLY THE E COAST AND THE STRAITS 
OF FLORIDA. A WEAKENING UPPER LOW IS IN THE CENTRAL ATLC NEAR 
26N48W SUPPORTING A SURFACE TROUGH THAT EXTENDS FROM 31N43W TO A 
1010 MB LOW PRES NEAR 20N52W CONTINUING TO 14N56W. TO THE E OF 
THE UPPER LOW...AN UPPER RIDGE IS PROVIDING DIFFLUENCE ALOFT TO 
SUPPORT SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS N 
OF 23N BETWEEN 40W AND 45W...MORE CONCENTRATED N OF 30N. A 
SURFACE RIDGE DOMINATES THE E ATLC ANCHORED BY A 1026 MB HIGH 
NEAR 30N20W. THIS HIGH PRES WILL MOVE NE OF AREA IN ABOUT 24 
HOURS. FRESH TRADE WINDS ARE BLOWING ON THE SOUTHERN PERIPHERY 
OF THE RIDGE. THE COLD FRONT ACROSS THE W ATLC WILL GRADUALLY 
DISSIPATE THROUGH SUN. A STRONGER COLD FRONT WILL MOVE OFF THE 
COAST OF N FLORIDA TUE. FRESH TO STRONG WINDS ARE EXPECTED ON 
EITHER SIDE OF THE FRONT. 

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

$$
GR