000 AXNT20 KNHC 201129 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 AM EST SAT DEC 20 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 1045 UTC. ...THE ITCZ... ITCZ IS CENTERED ALONG 9N12W 6N24W 6N35W 10N48W 6N59W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-8N BETWEEN 15W-24W. SCATTERED MODERATE CONVECTION IS FROM 2N-10N BETWEEN 28W-37W. SCATTERED MODERATE CONVECTION IS ALSO WITHIN 120 NM EITHER SIDE OF THE ITCZ AXIS BETWEEN 42W-50W. SCATTERED MODERATE CONVECTION IS ALSO WITHIN 120 NM EITHER SIDE OF THE ITCZ AXIS BETWEEN 55W-58W. ...DISCUSSION... GULF OF MEXICO... A 1021 MB SURFACE HIGH IS OVER THE E GULF NEAR 28N83W...AND A 1021 MB SURFACE HIGH IS OVER THE W ATLC NEAR 28N74W. BROAD SURFACE ANTICYCLONIC FLOW AROUND THESE SURFACE HIGHS COVERS MUCH OF THE GULF REGION. ALSO...SUBSIDENCE ASSOCIATED WITH THESE SURFACE HIGHS IS RESULTING IN ATMOSPHERIC STABILITY AND FAIR WEATHER CONDITIONS ACROSS MUCH OF THE GULF REGION. THIS STABILITY IS BEING ENHANCED IN THE VICINITY OF A BROAD UPPER LEVEL RIDGE EXTENDING ACROSS THE GULF REGION FROM AN UPPER HIGH CENTERED NW OF HISPANIOLA NEAR 21N73W. THIS UPPER RIDGE IS ASSOCIATED WITH RELATIVELY LIGHT AND BROAD ANTICYCLONIC FLOW ALOFT...AND DEEP LAYER DRY AIR...AFFECTING MUCH OF THE GULF REGION. FARTHER TO THE N...A DEEP LONGWAVE TROUGH WITH AN ASSOCIATED STRONG UPPER LEVEL JET MAXIMUM OVER THE CENTRAL CONUS IS SUPPORTING A SURFACE FRONT EXTENDING FROM THE MID-ATLANTIC STATES ACROSS THE SOUTHERN PLAINS AND INTO THE SOUTHERN ROCKY MOUNTAIN REGION OF THE CONUS. THE FRONT IS EXPECTED TO MOVE SOUTHWARD ACROSS THE GULF ON SUNDAY AND MONDAY AS A COLD FRONT. INCREASED NE SURFACE WINDS ARE FORECAST IN THE WAKE OF THE COLD FRONT...WITH GALE FORCE WINDS EXPECTED SUNDAY AFTERNOON AND NIGHT FOR PORTIONS OF THE NW GULF. CARIBBEAN SEA... SUBSIDENCE IN WESTERLY FLOW ALOFT AND ATMOSPHERIC STABILITY COVER THE CARIBBEAN REGION...WHERE GENERALLY DEEP LAYER DRY AIR IS PRESENT. THESE FACTORS ARE RESULTING IN FAIR WEATHER CONDITIONS ACROSS MUCH THE CARIBBEAN REGION. THE SOUTHERN PERIPHERY OF THE BROAD SURFACE ANTICYCLONIC FLOW AROUND THE AFOREMENTIONED SURFACE HIGHS OVER THE E GULF AND W ATLC IS BRINGING NE SURFACE WINDS OF 10 TO 20 KT TO THE CARIBBEAN REGION...EXCEPT UP TO 25 KT NEAR THE COAST OF COLOMBIA. UPPER LEVEL MOISTURE IS STREAMING NORTHWARD FROM SOUTH AMERICA INTO THE SE CARIBBEAN...WITH ISOLATED SHOWERS ACROSS THE S CARIBBEAN S OF 12N E OF 68W. ALSO...A SURFACE TROUGH EXTENDS FROM THE W ATLC NEAR 27N58W TO 22N63W TO THE NE CARIBBEAN NEAR 17N66W...WITH SATELLITE IMAGERY DEPICTING CYCLONIC MOTION OF CLOUDS IN THE VICINITY OF THIS SURFACE TROUGH. LOW LEVEL CONVERGENCE IS RESULTING IN ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ATLANTIC OCEAN... A 1021 MB SURFACE HIGH IS CENTERED IN THE W ATLC NEAR 28N74W... WITH A 1021 MB SURFACE HIGH IN THE E GULF OF MEXICO NEAR 28N83W. THESE SURFACE HIGHS ARE BRINGING SUBSIDENCE AND FAIR WEATHER CONDITIONS TO MUCH OF THE W ATLC. THIS SUBSIDENCE IS BEING ENHANCED IN THE VICINITY OF THE UPPER HIGH NW OF HISPANIOLA NEAR 21N73W. NORTHERLY UPPER LEVEL FLOW TO THE E OF THIS UPPER HIGH IS ADVECTING UPPER LEVEL MOISTURE ACROSS PORTIONS OF THE W ATLC. FARTHER TO THE E...A SURFACE TROUGH OVER THE CENTRAL ATLC EXTENDS FROM 29N46W TO 26N48W TO 22N48W. LOW LEVEL CONVERGENCE ASSOCIATED WITH THIS SURFACE TROUGH IS RESULTING IN NUMEROUS SHOWERS FROM 21N-30N BETWEEN 39W-44W. THIS ACTIVITY IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY IN THE VICINITY OF AN UPPER TROUGH WITH AN AXIS EXTENDING FROM 18N60W TO 27N48W TO 32N45W TO N OF THE DISCUSSION AREA. ALSO...UPPER LEVEL DIVERGENCE ASSOCIATED WITH AN 80-90-KT UPPER LEVEL JET MAXIMUM E OF THE UPPER TROUGH AXIS IS SUPPORTING THIS ACTIVITY...ALONG WITH LOW LEVEL CONVERGENCE ASSOCIATED WITH A WEAKENING SURFACE STATIONARY FRONT EXTENDING FROM NW OF THE DISCUSSION AREA TO 32N58W TO 31N56W AND A SURFACE COLD FRONT EXTENDING FROM 32N45W TO NE OF THE DISCUSSION AREA. ACROSS THE E ATLC...SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE EXTENDING SOUTHWESTWARD FROM A 1036 MB SURFACE HIGH NEAR 45N10W IS GENERALLY INHIBITING DEEP CONVECTION N OF 16N E OF 35W. HOWEVER...ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LOW NEAR 31N18W IS RESULTING IN SCATTERED SHOWERS N OF 28N BETWEEN 16W-22W. THIS ACTIVITY IS BEING ENHANCED BY LOW LEVEL CONVERGENCE IN THE VICINITY OF A SURFACE TROUGH EXTENDING FROM 31N11W TO 32N10W TO NE OF THE DISCUSSION AREA. FARTHER TO THE S...A SURFACE TROUGH EXTENDS FROM 27N58W TO 22N63W TO THE NE CARIBBEAN NEAR 17N66W...WITH SATELLITE IMAGERY DEPICTING CYCLONIC MOTION OF CLOUDS IN THE VICINITY OF THIS SURFACE TROUGH. LOW LEVEL CONVERGENCE IS RESULTING IN ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ALSO...AN UPPER RIDGE IS S OF 14N BETWEEN 19W-51W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS UPPER RIDGE IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ. $$ COHEN