000
AXNT20 KNHC 171757
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST WED DEC 17 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 8N12W 4N22W 5N43W 3N51W. BROAD AREA OF 
SCATTERED MODERATE WITH EMBEDDED CLUSTERS OF SCATTERED STRONG 
CONVECTION ARE FROM 1N-7N BETWEEN 15W-35. SCATTERED 
MODERATE/ISOLATED STRONG CONVECTION IS FROM 4N-6N BETWEEN 
37W-41W. 

...DISCUSSION...

GULF OF MEXICO...
MODERATE WLY MID/UPPER FLOW COVERS THE GULF ON THE N PERIPHERY 
OF AN UPPER RIDGE EXTENDING FROM CENTRAL AMERICA COVERING THE W 
CARIBBEAN AS WELL AS MEXICO. IN THE LOWER LEVELS...A STATIONARY 
FRONT ENTERS THE GULF ACROSS CENTRAL LOUISIANA SSW TO INLAND 
OVER MEXICO N OF TAMPICO THEN N ALONG THE E SLOPES OF THE SIERRA 
MADRE MOUNTAINS. THIS FRONT HAS LOST ITS UPPER SUPPORT. THE 
SURFACE RIDGE IS ONCE AGAIN IN CONTROL OF THE REMAINDER OF THE 
GULF. DENSE LOW LEVEL CLOUD COVER AND SCATTERED/ISOLATED SHOWERS 
ARE W OF THE FRONTAL BOUNDARY WITH LOW LEVEL ISOLATED SHOWERS 
MOVING ACROSS S FLORIDA AND THROUGH THE FLORIDA STRAITS ON THE 
ELY SURFACE FLOW. 

CARIBBEAN SEA...
ABUNDANT STABLE AIR ALOFT DOMINATES THE CARIBBEAN INCLUDING 
CENTRAL AND PORTIONS OF SOUTH AMERICA. THE W CARIBBEAN IS 
DOMINATED BY AN UPPER RIDGE THAT EXTENDS FROM THE E PACIFIC 
REGION ACROSS CENTRAL AMERICA AND INTO THE GULF OF MEXICO. THE 
UPPER TROUGH OVER THE W/CENTRAL ATLC REMAINS OVER THE REMAINDER 
OF THE CARIBBEAN E OF 75W ACROSS THE LESSER ANTILLES INTO THE W 
TROPICAL ATLC. THE PRESSURE GRADIENT BETWEEN SURFACE RIDGE OVER 
THE W ATLC AND RELATIVE LOWER PRESSURE OVER THE W CARIBBEAN 
CONTINUES TO MAINTAIN MODERATE/STRONG ELY TRADE WINDS ACROSS THE 
AREA W OF 75W. TYPICAL PATCHES OF LOW LEVEL CLOUDS AND EMBEDDED 
QUICK MOVING ISOLATED SHOWERS ARE BEING DRIVEN BY THESE 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 W ATLC W OF 75W. THE SURFACE RIDGE OVER 
THE NW ATLC CONTINUES TO PRODUCE MODERATE ELY WINDS ACROSS THE W 
ATLC AND GENERATING LOW LEVEL ISOLATED SHOWERS TO ALONG THE E 
COAST OF FLORIDA. AN UPPER TROUGH REMAINS OVER THE W/CENTRAL 
ATLC WITH AN EMBEDDED UPPER LOW CO-LOCATED WITH A 1008 MB 
SURFACE LOW NEAR 25N59W AND A SURFACE TROUGH EXTENDING FROM 
31N56W THROUGH THE SURFACE LOW TO 20N61W. THE TIGHT PRESSURE 
GRADIENT BETWEEN THIS SURFACE SYSTEM AND THE SURFACE RIDGES OVER 
THE FAR W AND ALL OF THE E ATLC ARE KEEPING NLY GALE FORCE WINDS 
N OF 25N BETWEEN 58W-67W BUT ARE EXPECTED TO BE BELOW GALE FORCE 
IN THE NEXT FEW HOURS. PATCHES OF SCATTERED SHOWERS AND POSSIBLE 
ISOLATED THUNDERSTORMS ARE N OF 24N BETWEEN 50W-65W. THE SURFACE 
LOW SHOULD TRACK SW OPENING UP INTO A TROUGH THU JUST NE OF THE 
LEEWARD ISLANDS. 

$$
WALLACE