000
AXNT20 KNHC 171121
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL  
705 AM EST THU DEC 17 2009

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...METEOROLOGICAL ANALYSIS...WEATHER 
OBSERVATIONS...AND RADAR.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1030 UTC.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 5N8W 5N22W 7N36W 2N54W. 
SCATTERED MODERATE CONVECTION IS WITHIN 60 NM EITHER SIDE OF THE 
AXIS BETWEEN 19W-26W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 0900 UTC...A 1013 MB LOW IS CENTERED OFF THE COAST OF 
BROWNSVILLE TEXAS NEAR 26N96W. A STATIONARY FRONT EXTENDS S FROM 
THE LOW INTO THE BAY OF CAMPECHE TO INLAND MEXICO ALONG 22N94W 
17N94W. A WAVY STATIONARY FRONT ALSO EXTENDS NE FROM THE LOW 
ALONG 27N94W 28N89W TO NEAR TAMPA FLORIDA CONTINUING INTO THE W 
ATLC. A SURFACE TROUGH EXTENDS BETWEEN THE TWO FRONTAL 
BOUNDARIES FROM 24N88W TO 25N93W DEPICTING A LINE OF CONFLUENT 
WINDS. AN UPPER LEVEL TROUGH CURRENTLY EXTENDING DOWN CENTRAL 
TEXAS AND ERN MEXICO SUPPORTS THE SURFACE LOW AND FRONTAL 
BOUNDARIES. MOIST SWLY AND DIFFLUENT FLOW ALOFT ON THE E SIDE OF 
THE UPPER TROUGH IS ENHANCING WIDESPREAD SHOWERS ACROSS THE W 
AND CENTRAL GULF W OF 87W. SCATTERED THUNDERSTORMS ARE ALSO 
AHEAD OF THE FRONT IN THE SW GULF BETWEEN THE FRONT AND THE 
YUCATAN PENINSULA...AND NEAR THE SURFACE TROUGH FROM 24N-26N 
BETWEEN 91W-93W. A SECOND SURFACE TROUGH PARALLELS THE SE 
FLORIDA COAST FROM NEAR FREEPORT BAHAMAS TO MIAMI TO SW OF KEY 
WEST. A LINE OF ISOLATED SHOWERS/THUNDERSTORMS IS ALONG THE 
TROUGH AXIS. THE TIGHT PRESSURE GRADIENT BETWEEN THE LOW 
PRESSURE IN THE NW GULF AND HIGH PRESSURE OVER TEXAS IS 
SUPPORTING GALE FORCE WINDS ACROSS THE W GULF FROM 26N-28N W OF 
92W...AND S OF 22N W OF THE FRONT. EXPECT THE GULF TO REMAIN 
MOIST WITH WIDESPREAD PRECIPITATION OVER THE NEXT COUPLE OF DAYS 
AS THE LOW CENTER IN THE NW GULF DEEPENS AND BEGINS MOVING E 
LATER TODAY ONCE THE UPPER LEVEL TROUGH OVER TEXAS CATCHES UP 
WITH THE SURFACE FEATURE.

CARIBBEAN SEA...
MODERATE TO FRESH TRADEWINDS CONTINUE ACROSS THE CARIBBEAN DUE 
TO A MODERATE PRESSURE GRADIENT BETWEEN LOW PRESSURE OVER NRN 
COLOMBIA AND A WEAK SURFACE RIDGE IN THE W ATLC. WINDS ARE 
FORECAST TO DIMINISH AS THE PRESSURE GRADIENT WEAKENS DUE TO THE 
LOW PRESSURE SYSTEM IN THE GULF TRACKING EWD. MODERATE 
SUBSIDENCE AND DRY AIR CONTINUES TO DOMINATE THE MAJORITY OF THE 
BASIN AROUND AN UPPER LEVEL RIDGE ALONG 65W. MOISTURE FROM THE 
GULF OF MEXICO HAS BEGUN TO TRICKLE INTO THE NW CARIBBEAN 
ENHANCING ISOLATED SHOWERS/THUNDERSTORMS OFF THE N COAST OF 
HONDURAS. A LINE OF SHOWERS EMBEDDED IN THE ELY SURFACE FLOW 
CONTINUES TO MOVE QUICKLY FROM THE CENTRAL LESSER ANTILLES TO S 
OF JAMAICA. ENHANCED MOISTURE WILL CONTINUE TO ENTER THE NW 
CARIBBEAN AS THE AFOREMENTIONED LOW PRESSURE IN THE GULF PUSHES 
E INCREASING THE SHOWER ACTIVITY IN THAT PORTION OF THE BASIN.

ATLANTIC OCEAN...
A DEEP LAYERED TROUGH ACROSS THE NW ATLC SUPPORTS A COLD FRONT 
ENTERING THE SW N ATLC NEAR 32N55W CONTINUING ALONG 28N63W TO 
NEAR FREEPORT BAHAMAS. ISOLATED SHOWERS ARE WITHIN 90 NM OF THE 
FRONT AXIS. THE TAIL END OF A STATIONARY FRONT EXTENDING FROM 
THE GULF OF MEXICO ENTERS THE ATLC WATERS N OF THE COLD FRONT 
NEAR CAPE CANAVERAL.  FARTHER E...AN UPPER LEVEL TROUGH CENTERED 
N OF THE AZORES ISLANDS IS SUPPORTING A DEEPENED 999 MB LOW NW 
OF THE CANARY ISLANDS NEAR 31N25W. A COLD FRONT EXTENDS S OF THE 
LOW ALONG 26N28W 23N33W 22N41W. NUMEROUS SHOWERS/POSSIBLE 
THUNDERSTORMS ARE MAINLY E OF THE LOW IN THE DIFFLUENT ZONE 
ALOFT AROUND THE E SIDE OF THE DEEP LAYER TROUGH N OF 24N 
BETWEEN 14W-26W. 

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

$$
WALTON