000
AXNT20 KNHC 201748
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST THU DEC 20 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.

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

THE MONSOON TROUGH PASSES INLAND N OF THE GULF OF GUINEA AND 
EXITS THE SOUTHERN COAST OF LIBERIA NEAR 5N8W...THEN EXTENDS 
WESTWARD TO 4N11W. THE ITCZ CONTINUES TO 4N16W 4N25W 3N35W. 
SCATTERED MODERATE CONVECTION IS E OF 13W WITHIN 200 NM OFF THE 
COAST OF LIBERIA...COTE D'IVOIRE AND GHANA. SCATTERED SHOWERS 
ARE WITHIN 100 NM EITHER N OR S OF THE ITCZ BETWEEN 30W AND 
38W.  

...DISCUSSION...

THE GULF OF MEXICO...

IN THE MIDDLE TO UPPER LEVELS...A DEEP LAYER TROUGH IS OVER THE 
MISSISSIPPI VALLEY SUPPORTING A SURFACE COLD FRONT THAT ENTERS 
THE REGION THROUGH THE SOUTHEAST COAST OF LOUISIANA NEAR 29N90W. 
THE COLD FRONT EXTENDS SOUTHWESTWARD TO 26N93W 23N96W AND ENTERS 
THE E COAST OF MEXICO NEAR 21N97W. THE WIND FLOW ALOFT N OF 24N 
IS WESTERLY AND SOUTHWESTERLY E OF 90W. A PREFRONTAL TROUGH 
EXTENDS FROM PENSACOLA TO 27N90W 24N94W. A LINE OF HEAVY SHOWERS 
AND THUNDERSTORMS ARE WITHIN 60 NM OF THE TROUGH WITH A LINE OF 
SHOWERS ALONG THE FRONT. AT THE SURFACE...RETURN FLOW IS AHEAD 
OF THE FRONTAL AND PREFRONTAL SYSTEM WITH GALE WINDS WEST OF THE 
COLD FRONT. WITHIN 24 HOURS AND WHILE THE COLD FRONT MOVES 
ACROSS THE FLORIDA PENINSULA GALE FORCE WINDS WILL PREVAIL 
ACROSS A GOOD PORTION OF GULF. 

THE CARIBBEAN SEA...

AT THE UPPER LEVELS...WESTERLY FLOW IS OVER THE ENTIRE 
CARIBBEAN. WATER VAPOR IMAGERY SHOWS DRY AIR SUBSIDENCE N OF 13N 
ACROSS THE REGION SUPPORTING FAIR WEATHER CONDITIONS FOR MOST OF 
THE REGION. SHOWERS AND THUNDERSTORMS ARE WITHIN 120 NM E OF THE 
COAST OF COSTA RICA AND PANAMA DUE TO WINDS BANKING ALONG THE 
COASTS. TRADE WINDS OF 15 KT TO 25 KT PREVAIL OVER THE ENTIRE 
REGION AND THE SURFACE PRESSURE GRADIENT CONTINUES TO BE WEAK 
ACROSS THE AREA. WITHIN 24 HOURS...NORTHEASTERLY WINDS WILL 
DEVELOP OVER THE WESTERN CARIBBEAN AND TRADE WINDS WILL PREVAIL 
ELSEWHERE ACROSS THE REGION. 

THE ATLANTIC OCEAN...

IN THE WESTERN ATLC A RIDGE WITH AXIS ALONG THE EASTERN COAST OF 
THE US GENERATES NORTHWESTERLY WINDS IN THE MIDDLE TO UPPER 
LEVELS SUPPORTING A 1021 MB HIGH LOCATED NORTHEAST OF THE 
BAHAMAS NEAR 29N75W. GALE WINDS ARE EXPECTED TO BUILD IN THIS 
AREA AS THE COLD FRONT THAT IS IN THE GULF CONTINUES TO MOVE 
EASTWARD TOWARDS THE FLORIDA PENINSULA IN LESS THAN 24 HOURS. 
ALOFT IN THE CENTRAL ATLC...A DEEP LAYER TROUGH SUPPORTS A COLD 
FRONT THAT ENTERS THE REGION NEAR 29N47W CONTINUING 
SOUTHWESTWARD TO 24N58W 20N66W. THIS COLD FRONT STARTS TO WEAKEN 
OVER LA HISPANIOLA. LIGHT SHOWERS ARE POSSIBLE ALONG THE FRONTAL 
BOUNDARY. IN THE EASTERN ATLC...A SHORT WAVE TROUGH ALOFT 
SUPPORTS A REGION OF PRECIPITATION FROM 20N TO 27N BETWEEN 17W 
AND 30W. 
IN THE TROPICAL ATLC...SCATTERED MODERATE CONVECTION IS WITHIN 
200 NM OFF THE COAST OF NORTHEASTERN VENEZUELA...GUYANA AND 
SURINAME.   

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

$$
NR/CW