000
AXNT20 KNHC 181122
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST THU DEC 18 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1100 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 7N12W 5N24W 5N40W 6N54W. SCATTERED 
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 150 NM N OF THE 
AXIS BETWEEN 18W-32W AND BETWEEN 37W-48W. NUMEROUS 
MODERATE/SCATTERED STRONG IS WITHIN 120 NM S OF THE AXIS E OF 
16W. ISOLATED MODERATE CONVECTION IS WITHIN 180 NM S OF THE AXIS 
BETWEEN 18W-46W.  

...DISCUSSION...

GULF OF MEXICO...
A LARGE AND FAIRLY AMPLIFIED MID TO UPPER HIGH IS CENTERED OVER 
THE BAY OF CAMPECHE PROVIDING MAINLY LIGHT FLOW AND STABLE AIR 
ALOFT....EXCEPT FOR OVER FLORIDA WHERE HIGH CLOUDINESS IS BEING 
DRIVEN S ON THE E PERIPHERY OF THE RIDGE. IN THE LOWER LEVELS... 
A DISSIPATING FRONT IS STILL STALLED ALONG THE TEXAS AND N 
MEXICO COASTS. SLIGHT LOW-LEVEL CONVERGENCE ALONG THE FRONT IS 
PRODUCING LOW-LEVEL CLOUDS AND LIGHT SHOWERS. OTHERWISE... 
MAINLY FAIR CONDITIONS EXIST ELSEWHERE WITH ONLY PATCHY 
LOW-LEVEL CLOUDS STEERED BY LIGHT TO MODERATE E FLOW ON THE 
S/SW SIDE OF A 1025 MB HIGH OVER THE SUBTROPICAL W ATLC. LITTLE 
SIGNIFICANT CHANGE IS EXPECTED OVER THE NEXT COUPLE OF DAYS 
UNTIL THE NEXT COLD FRONT APPROACHES THE NW GULF THIS WEEKEND.

CARIBBEAN SEA...
CONFLUENCE NEAR THE BASE OF AN UPPER TROUGH OVER THE CENTRAL 
ATLC IS ENHANCING SUBSIDENCE ACROSS THE ENTIRE AREA...LIMITING 
THE DEVELOPMENT OF ANY DEEP CONVECTION. HOWEVER...SCATTERED 
SHOWERS AND ISOLATED LOW TOPPED TSTMS ARE AFFECTING MUCH OF THE 
AREA...BENEATH THE MID-LEVEL CAP...GENERATED BY AN ELONGATED SFC 
TROUGH OVER THE CENTRAL ATLC AND DRIVEN S/SW ON THE W SIDE OF 
THE CIRCULATION. RECENT SCATTEROMETER DATA INDICATED THAT THESE 
N TO NE WINDS ARE MAINLY IN THE 20-25 KT RANGE W OF 
67W...STRONGEST NEAR THE PASSAGES. SIMILAR WINDS/SHOWERS ARE 
EXPECTED OVER THE NEXT COUPLE OF DAYS BEFORE HIGH PRES SHIFTS S 
OVER THE W ATLC...ALLOWING THE FLOW TO WEAKEN AND VEER E.     

ATLANTIC OCEAN...
DEEP LAYER LOW PRESSURE OVER THE CENTRAL ATLC IS CAUSING SOME 
ACTIVE WEATHER THIS MORNING...BUT LESS SO THAN A DAY OR TWO 
AGO. THE SFC CENTER IS ANALYZED 1010 MB NEAR 26N60W WITH ITS 
ASSOCIATED TROUGH EXTENDING BOTH N TO 32N58W AND S TO 19N62W. 
SCATTEROMETER AND TO SOME DEGREE SFC OBS SHOW A FAIRLY WELL 
DEFINED SFC CIRCULATION WITHIN AN INCREASINGLY ELONGATED TROUGH. 
LOW-LEVEL CONVERGENCE AND INSTABILITY NEAR THE LOW IS PRODUCING 
SCATTERED SHOWERS AND TSTMS WITHIN 240 NM OF THE CENTER. A 
LARGER AREA OF SHOWERS AND TSTMS EXIST FARTHER E FROM 17N-26N 
BETWEEN 46W-51W IN AN UPPER DIFFLUENT ZONE AND POSSIBLY ENHANCED 
BY A LOW-LEVEL TROUGH ALONG 54W. THE LOW IS EXPECTED BECOME 
GREATLY SHEARED AND SPLIT APART BY A SHORTWAVE TROUGH FRI AND 
THIS WEEKEND. THE W ATLC IS RELATIVELY TRANQUIL BENEATH ABUNDANT 
DRY AIR ALOFT ON THE W SIDE OF THE UPPER LOW. HOWEVER...AS 
MENTIONED ABOVE... STRONG N/NE LOW-LEVEL WINDS AND INSTABILITY 
ARE STIRRING UP SCATTERED SHOWERS AND ISOLATED LOW-TOPPED TSTMS 
MAINLY E OF 75W. OVER THE TROPICAL E ATLC...STRONG WLY FLOW 
ALOFT IS TRANSPORTING WIDESPREAD MID-HIGH LEVEL CLOUDINESS AND 
ENHANCING ITCZ CONVECTION.

$$
CANGIALOSI