000
AXNT20 KNHC 240002
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST TUE DEC 23 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2315 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 8N12W 5N20W 3N35W 2N43W TO THE EQUATOR AT 
49W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-6N 
BETWEEN 23W-30W. SIMILAR CONVECTION IS FROM 7N-9N BETWEEN 
33W-36W.
  
...DISCUSSION...

GULF OF MEXICO...
WEST-SOUTHWESTERLY FLOW ALOFT PREVAILS ACROSS MUCH OF THE GULF 
REGION. AT THE SAME TIME...MID/UPPER LEVEL MOISTURE CONTINUES TO 
STREAM ACROSS THE N GULF...AS A VIGOROUS DEEP-LAYER TROUGH OVER 
THE CENTRAL CONUS TRANSLATES EASTWARD. MOST OF THE ENERGY WITH 
THIS SYSTEM REMAINS NORTH OF THE GULF REGION. HOWEVER...A 
SURFACE COLD FRONT EXTENDS SOUTHWARD FROM A 1014 MB SURFACE LOW 
IN E TEXAS NEAR 31N96W. THIS COLD FRONT ENTERS THE NW GULF FROM 
SE TEXAS NEAR 29N96W...EXTENDING SOUTHWARD TO 28N96W. ALSO...A 
SURFACE TROUGH IN THE W GULF EXTENDS FROM 29N94W TO 25N95W TO 
21N95W. A RECENT QUIKSCAT PASS INDICATES SURFACE CONFLUENCE 
ALONG THIS SURFACE TROUGH. ALSO...A NEARLY CONTINUOUS BAND OF 
CLOUDS AND ISOLATED SHOWERS ARE PRESENT ALONG AND WITHIN 30 NM 
EITHER SIDE OF THIS SURFACE TROUGH. HOWEVER...DEEP CONVECTION IS 
BEING SUPPRESSED ACROSS MUCH OF THE GULF REGION...WHERE 
SUBSIDENCE PREVAILS. THIS SUBSIDENCE IS BEING SUPPORTED BY A 
SURFACE RIDGE EXTENDING ACROSS THE GULF FROM A 1040 MB HIGH NE 
OF NORTH CAROLINA NEAR 37N75W...AS WELL AS BY AN UPPER HIGH OVER 
THE BAY OF CAMPECHE NEAR 19N95W. THE FLOW AROUND THE SURFACE 
HIGH IS SUPPORTING SOUTHEASTERLY SURFACE WINDS OF 15 TO 25 KT 
ACROSS MUCH OF THE GULF REGION...WITH UP TO 30 KT ACROSS 
PORTIONS OF THE NE GULF. DEEP LAYER DRY AIR IS ALSO SUPPRESSING 
CONVECTION ACROSS MUCH OF THE SE GULF.

CARIBBEAN SEA...
BROAD AND LIGHT ANTICYCLONIC FLOW ALOFT COVERS MUCH OF THE 
CARIBBEAN REGION AROUND AN UPPER HIGH CENTERED IN N VENEZUELA 
NEAR 11N69W. SUBSIDENCE AND DEEP LAYER DRY AIR ASSOCIATED WITH 
THIS HIGH ARE LIMITING DEEP CONVECTION ACROSS MUCH OF THE 
CARIBBEAN. HOWEVER...NE TO E SURFACE WINDS OF 20 TO 30 KT ARE 
ADVECTING PATCHES OF SHALLOW LOW-LEVEL MOISTURE WITH EMBEDDED 
SHOWERS ACROSS THE CARIBBEAN...WITH THE GREATEST CONCENTRATION 
OF THIS MOISTURE AND THESE SHOWERS ACROSS THE E CARIBBEAN. 
ALSO...LOW LEVEL CONVERGENCE ASSOCIATED WITH A 1011 MB SURFACE 
LOW IN N COLOMBIA NEAR 9N75W IS SUPPORTING ISOLATED SHOWERS 
ACROSS THE SW CARIBBEAN S OF 11N BETWEEN 75W-83W.
 
ATLANTIC OCEAN...
WESTERLY FLOW ALOFT IS PRESENT ACROSS THE W ATLC...AS A VIGOROUS 
DEEP LAYER TROUGH N OF THE DISCUSSION AREA MOVES NORTHEASTWARD. 
AN ASSOCIATED SURFACE COLD FRONT ENTERS THE DISCUSSION AREA NEAR 
32N52W AND EXTENDS SOUTHWESTWARD TO 26N62W TO NE CUBA NEAR 
21N76W. LOW LEVEL CONVERGENCE IS RESULTING IN ISOLATED SHOWERS 
WITHIN 60 NM EITHER SIDE OF THIS COLD FRONT. ALSO...LOW LEVEL 
INSTABILITY RESULTING FROM COLD AIR ADVECTION OVER THE 
RELATIVELY WARMER W ATLC WATERS IS RESULTING IN A BROKEN LAYER 
OF STRATOCUMULUS CLOUDS BETWEEN THE COLD FRONT AND THE E COAST 
OF THE CONUS. HOWEVER...W OF THE COLD FRONT...DEEP CONVECTION IS 
GENERALLY BEING SUPPRESSED BY THE COMBINATION OF SUBSIDENCE AND 
DEEP LAYER DRY AIR. THIS SUBSIDENCE IS BEING ENHANCED BY A 
SURFACE RIDGE EXTENDING ACROSS THE W ATLC FROM A 1040 MB SURFACE 
HIGH NE OF N CAROLINA NEAR 37N75W. FARTHER TO THE E...A SURFACE 
TROUGH OVER THE CENTRAL ATLC EXTENDS FROM 27N49W TO 22N50W TO 
17N49W. LOW LEVEL CONVERGENCE IS SUPPORTING ISOLATED SHOWERS 
WITHIN 90 NM EITHER SIDE OF THIS SURFACE TROUGH. ACROSS THE E 
ATLC...GENERALLY FAIR WEATHER CONDITIONS ARE OCCURRING N OF 12N 
E OF 39E AS A RESULT OF SUBSIDENCE NEAR A SURFACE RIDGE 
ASSOCIATED WITH A 1030 MB SURFACE HIGH NEAR 37N33W. HOWEVER...AN 
UPPER LOW IS CENTERED BETWEEN THE MADEIRA AND THE AZORES ISLANDS 
NEAR 35N18W...WITH AN UPPER TROUGH EXTENDING FROM THIS UPPER LOW 
TO 32N19W TO 25N23W TO 19N39W. THE UPPER LOW AND UPPER TROUGH 
ARE SUPPORTING A SURFACE COLD FRONT THAT EXTENDS FROM 32N19W TO 
29N25W TO 30N34W. ATMOSPHERIC INSTABILITY ASSOCIATED WITH THE 
UPPER LOW AND UPPER TROUGH...AND LOW LEVEL CONVERGENCE 
ASSOCIATED WITH THE SURFACE COLD FRONT...ARE SUPPORTING 
SCATTERED SHOWERS N OF 27N BETWEEN 15W-23W. THIS ACTIVITY IS 
BEING ENHANCED BY UPPER LEVEL DIVERGENCE ASSOCIATED WITH A 
90-100-KT UPPER LEVEL JET MAXIMUM W OF THE UPPER LOW. FARTHER TO 
THE S...A BROAD UPPER LEVEL RIDGE IS S OF 14N E OF 26W. UPPER 
LEVEL DIFFLUENCE W OF THIS RIDGE IS ENHANCING THE CONVECTION 
ASSOCIATED WITH THE ITCZ.

$$
COHEN