000
AXNT20 KNHC 170538
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL  
105 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0500 UTC.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 8N13W 5N23W 4N35W 3N50W. 
SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 60 NM N OF THE 
AXIS BETWEEN 21W-27W.
...DISCUSSION...

GULF OF MEXICO...
AS OF 0300 UTC...A 1015 MB LOW IS CENTERED OFF THE COAST OF 
BROWNSVILLE TEXAS NEAR 25N95W. A STATIONARY FRONT EXTENDS S FROM 
THE LOW INTO THE BAY OF CAMPECHE TO INLAND MEXICO NEAR 17N93W. A 
STATIONARY FRONT ALSO EXTENDS E FROM THE LOW ALONG 26N TO S OF 
FORT MYERS FLORIDA CONTINUING INTO THE W ATLC. AN UPPER LEVEL 
TROUGH CURRENTLY EXTENDING DOWN E TEXAS AND CENTRAL MEXICO 
SUPPORTS THE SURFACE LOW AND FRONTAL BOUNDARIES. MOIST SWLY AND 
DIFFLUENT FLOW ALOFT ON THE E SIDE OF THE UPPER TROUGH IS 
ENHANCING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ACROSS THE 
MAJORITY OF THE W AND CENTRAL GULF WITH ISOLATED SHOWERS 
CONTINUING ACROSS THE ERN GULF. THE TIGHT PRESSURE GRADIENT 
BETWEEN THE LOW PRESSURE IN THE NW GULF AND HIGH PRESSURE OVER 
TEXAS AND NRN MEXICO IS SUPPORTING GALE FORCE WINDS ACROSS THE W 
GULF S OF 26N W OF THE FRONT AXIS. 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 
ONCE THE UPPER LEVEL TROUGH OVER E TEXAS AND MEXICO CATCHES UP 
WITH THE SURFACE FEATURE.

CARIBBEAN SEA...
MODERATE TO FRESH TRADEWINDS CONTINUE ACROSS THE CARIBBEAN DUE 
TO THE STRONG PRESSURE GRADIENT BETWEEN LOW PRESSURE OVER NRN 
COLOMBIA AND HIGH PRESSURE 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. HOWEVER...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 BEGIN TO ENTER THE NW CARIBBEAN AS THE 
AFOREMENTIONED LOW PRESSURE IN THE GULF PUSHES E INCREASING THE 
CHANCE FOR SHOWERS 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 32N59W CONTINUING ALONG 28N68W 
BECOMING STATIONARY NEAR FREEPORT BAHAMAS AND ACROSS S FLORIDA. 
ISOLATED SHOWERS ARE WITHIN 90 NM OF THE FRONT AXIS. S OF THE 
FRONT...WEAK HIGH PRESSURE PREVAILS CENTERED NEAR A 1021 MB HIGH 
AT 24N66W. FARTHER E...A SHORTWAVE UPPER TROUGH EMBEDDED IN A 
DEEP LAYER TROUGH IS SUPPORTING A 1004 MB LOW W OF THE CANARY 
ISLANDS NEAR 28N31W. A FORMING COLD FRONT EXTENDS S OF THE LOW 
ALONG 23N37W 22N45W. A FORMING WARM FRONT EXTENDS TO THE N OF 
THE LOW CENTER TO NEAR 31N27W. 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 23N 
BETWEEN 17W-29W. AS THIS SYSTEM MOVES NE AND CATCHES UP WITH THE 
DEEP LAYER TROUGH IT IS FORECAST TO DEEPEN AND BECOME THE 
DOMINANT SURFACE SYSTEM.

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

$$
WALTON