000
AXNT20 KNHC 151720
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST MON DEC 15 2008

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1645 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 9N13W 4N23W 6N45W 4N52W. AN AREA OF 
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS MOSTLY ALONG 
THE ITCZ WITHIN 120 NM OF LINE FROM 4N19W 4N33W TO 7N43W. 

...DISCUSSION...

GULF OF MEXICO...
MODERATE/STRONG WLY MID/UPPER FLOW COVERS THE GULF WITH STRONGER 
WINDS OVER THE GULF COAST STATES FROM TEXAS TO THE FLORIDA 
PANHANDLE ON THE N PERIPHERY OF AN UPPER HIGH CENTERED IN THE W 
CARIBBEAN. THIS FLOW IS SPREADING PACIFIC HIGH LEVEL MOISTURE 
ACROSS THE N GULF WITH DRIER AIR PRESENT IN LIGHTER FLOW OVER 
THE S HALF. IN THE LOWER LEVELS...A STRONG 1040 MB HIGH IS OVER 
THE NW ATLC PRODUCING SELY FLOW OVER THE E GULF. THIS MOIST 
LOW-LEVEL FLOW IS PRODUCING LOW-LEVEL CLOUDS WITH EMBEDDED 
SCATTERED SHOWERS OVER THE AREA N OF 25N E OF 92W. A STRONG COLD 
FRONT IS ALONG THE TEXAS COAST AT 15/1500 UTC AND WILL ENTER THE 
NW GULF OVER THE NEXT FEW HOURS. HOWEVER...THE FRONT IS NOT 
EXPECTED TO MAKE MUCH PROGRESS ACROSS THE GULF AS IT QUICKLY 
LOSES ITS UPPER SUPPORT. AN INCREASE IN SCATTERED SHOWERS AND 
POSSIBLE ISOLATED THUNDERSTORMS ARE LIKELY OVER THE NW WATERS 
NEAR THE BOUNDARY LATER TODAY INTO TUE AS THE FRONT STALLS THEN 
RETURNS N AS A WARM FRONT. 

CARIBBEAN SEA...
ABUNDANT STABLE AIR ALOFT DOMINATES THE ENTIRE CARIBBEAN. THE W 
CARIBBEAN IS DOMINATED BY AN UPPER RIDGE ANCHORED NEAR THE COAST 
OF NICARAGUA AND EXTENDS OVER THE GULF OF MEXICO. AN UPPER 
TROUGH OVER THE W ATLC DIPS S OVER THE E CARIBBEAN. THE PRESSURE 
GRADIENT BETWEEN STRONG SURFACE HIGH CENTERED WELL N OF THE AREA 
AND RELATIVE LOW PRESSURE OVER THE CARIBBEAN IS PRODUCING 
MODERATE/STRONG ELY TRADE WINDS ACROSS THE AREA AND WILL 
GRADUALLY DIMINISH BY MID WEEK. TYPICAL PATCHES OF LOW-LEVEL 
CLOUDS AND EMBEDDED QUICK MOVING ISOLATED SHOWERS ARE BEING 
DRIVEN BY THE TRADE WINDS...BUT THE LARGE SCALE SUBSIDENT 
ENVIRONMENT IS KEEPING THE MOISTURE SHALLOW. 

ATLANTIC OCEAN...
THE UPPER RIDGE THAT COVERS THE W CARIBBEAN AND THE GULF OF 
MEXICO EXTENDS OVER THE FAR W ATLC W OF 72W. A COMPLEX UPPER 
TROUGH OVER THE CENTRAL ATLC IS PROVIDING LIMITED SUPPORT FOR A 
WEAKENING COLD FRONT EXTENDING THROUGH 32N48W TO 25N56W. THE 
TIGHT PRESSURE GRADIENT BETWEEN THIS FRONT AND A 1040 MB HIGH 
WELL N OF THE REGION IS PRODUCING NELY GALE FORCE WINDS N OF 28N 
W OF FRONT TO 65W AND 20-25 KT ELSEWHERE W OF THE FRONT. THE 
SURFACE TROUGH REMAINS WELL DEFINED JUST E OF THE FRONT ALONG 
50W N OF 20N. SATELLITE IMAGES INDICATE AN INCREASED AREA OF 
CYCLONIC TURNING IN THE MID/UPPER LEVELS NEAR 27N59W WITH 
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 120 NM OF 
LINE FROM 22N60W TO BEYOND 32N48W. SIMILAR ACTIVITY IS FROM 
22N-29N BETWEEN 44W-49W IN AN UPPER DIFFLUENT ZONE. THIS SURFACE 
TROUGH WILL LIKELY GAIN VORTICITY FROM THE WEAKENING FRONT AND 
POSSIBLY DEVELOP INTO A CLOSED LOW ON TUE/EARLY WED ACCORDING TO 
MANY OF THE NWP MODELS. A SECOND SURFACE RIDGE IS OVER THE E 
ATLC ANCHORED BY A 1034 MB HIGH OVER THE AZORES. A WEAK SURFACE 
TROUGH IS EMBEDDED WITHIN THE ELY TRADE WIND FLOW OVER THE W 
TROPICAL ATLC FROM 16N50W TO 11N52W BUT IS NOT GENERATING ANY 
SIGNIFICANT WEATHER.  

$$
WALLACE