000
AXNT20 KNHC 160551
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST TUE DEC 16 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0545 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 10N14W 4N25W 5N35W 8N48W 6N58W. SCATTERED 
MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE ITCZ 
AXIS BETWEEN 13W-22W. SCATTERED MODERATE/ISOLATED STRONG 
CONVECTION IS FROM 2N-9N BETWEEN 23W-31W. SCATTERED MODERATE 
CONVECTION IS FROM 3N-11N BETWEEN 32W-44W.

...DISCUSSION...

GULF OF MEXICO...
A STRONG COLD FRONT IS DRAPED ACROSS THE NW GULF AND EXTENDS 
FROM A 1021 MB SURFACE LOW IN S LOUISIANA NEAR 30N92W TO 27N95W 
TO NE MEXICO NEAR 25N98W. TO THE NW OF THIS FRONT...N TO NE 
WINDS OF 20 TO 25 KT ARE ADVECTING MUCH COOLER AND DRIER 
CONDITIONS ACROSS THE NW GULF REGION...WITH SURFACE TEMPERATURES 
IN THE 30S ACROSS MUCH OF SE TEXAS. THIS MUCH COOLER AIRMASS IS 
CHARACTERIZED AS A MODIFIED CONTINENTAL POLAR AIRMASS...AND IS 
BEING ANCHORED BY A 1042 MB SURFACE HIGH OVER THE CENTRAL PLAINS 
OF THE CONUS. THE FRONT HAS BEEN MAKING SLOWER PROGRESS TO THE 
SE...AND IS FORECAST TO BECOME STATIONARY OVER THE NW GULF OVER 
THE NEXT DAY...AS THE SURFACE HIGH TAKES MORE OF AN EASTWARD 
TRAJECTORY ACROSS THE NE CONUS. IN THE MEANTIME...MODERATE 
WESTERLY FLOW ALOFT CONTINUES ACROSS THE GULF REGION...AS UPPER 
LEVEL MOISTURE IS STREAMING ACROSS THE N GULF. HOWEVER...DRY AIR 
IN THE LOW/MID ACROSS THE ENTIRE GULF IS INHIBITING DEEP 
CONVECTION AREAWIDE...DESPITE THE PRESENCE OF THE FRONT OVER THE 
NW GULF.   

CARIBBEAN SEA...
GENERALLY FAIR WEATHER CONDITIONS ARE IN PLACE ACROSS THE ENTIRE 
CARIBBEAN...AS A SURFACE RIDGE OVER THE CENTRAL ATLC EXTENDS 
INTO THE NE CARIBBEAN...WITH MODERATE TO FRESH TRADE WINDS  
PRESENT ACROSS THE CARIBBEAN REGION. THIS SURFACE RIDGE IS 
INDUCING LOW LEVEL SUBSIDENCE THAT IS BEING REINFORCED BY 
SUBSIDENCE IN WESTERLY AND NORTHWESTERLY ALOFT ACROSS THE 
CARIBBEAN. IN ADDITION TO THE AFOREMENTIONED SUBSIDENCE...DEEP 
LAYER DRY AIR IS INHIBITING DEEP CONVECTION ACROSS MUCH OF THE 
CARIBBEAN. HOWEVER...ISOLATED SHOWERS ARE OCCURRING OVER THE W 
CARIBBEAN S OF 14N W OF 76W IN RESPONSE TO SUFFICIENT UPPER 
LEVEL DIVERGENCE ASSOCIATED WITH AN UPPER RIDGE OVER THE W 
CARIBBEAN. THIS RIDGE EXTENDS FROM N OF PANAMA NEAR 10N79W TO 
17N33W.
 
ATLANTIC OCEAN...
SUBSIDENCE IN STRONG NORTHWESTERLY FLOW ALOFT IS RESULTING IN 
GENERALLY FAIR WEATHER CONDITIONS ACROSS THE W ATLC...WITH UPPER 
LEVEL MOISTURE STREAMING INTO THE W ATLC FROM THE E GULF AND SE 
CONUS. FARTHER TO THE E...A SURFACE COLD FRONT EXTENDS FROM N OF 
PUERTO RICO NEAR 21N67W TO 22N58W TO 31N52W AND EXTENDS NE OF 
THE DISCUSSION AS A STATIONARY FRONT. TO THE E OF THIS FRONT...A 
PERSISTENT SURFACE TROUGH EXTENDS FROM 28N51W TO 24N51W TO 
19N49W. LOW LEVEL CONVERGENCE ASSOCIATED WITH THE SURFACE FRONT 
AND SURFACE TROUGH IS RESULTING IN SCATTERED SHOWERS AND 
ISOLATED THUNDERSTORMS N OF 22N BETWEEN 45W-59W. THIS ACTIVITY 
IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN 
UPPER TROUGH N OF 18N BETWEEN 47W-63W. OVER THE NEXT TWO 
DAYS...STRONG UPPER LEVEL DIVERGENCE ASSOCIATED WITH AN UPPER 
LEVEL JET MAXIMUM IN THE BASE OF THIS UPPER TROUGH IS FORECAST 
TO INDUCE SUFFICIENT SURFACE PRESSURE FALLS IN THE VICINITY OF 
THE SURFACE TROUGH AND COLD FRONT TO RESULT IN THE DEVELOPMENT 
OF A SURFACE LOW IN THE CENTRAL ATLC. ACCORDINGLY...THE 
TIGHTENING SURFACE PRESSURE GRADIENT AROUND THIS DEVELOPING 
SURFACE LOW IS RESULTING GALE FORCE WINDS OVER PORTIONS OF THE 
CENTRAL ATLC NEAR THE AFOREMENTIONED SURFACE FRONT N OF 27N. 
FARTHER TO THE E...A SURFACE RIDGE IS BRINGING SUBSIDENCE TO THE 
E ATLC AROUND A 1032 MB SURFACE HIGH NEAR THE AZORES 37N27W. 
THIS SUBSIDENCE...COMBINED WITH DEEP LAYER DRY AIR...IS 
RESULTING IN FAIR WEATHER ACROSS MUCH OF THE E ATLC. OVER THE 
TROPICAL ATLC...RIDGE S OF 12N BETWEEN 13W-44W. UPPER LEVEL 
DIVERGENCE ASSOCIATED WITH THE RIDGE IS THE ENHANCING CONVECTION 
ASSOCIATED WITH THE ITCZ.

$$
COHEN