000 AXNT20 KNHC 061154 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 AM EST SUN DEC 06 2009 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 0945 UTC. ...ITCZ... THE INTERTROPICAL CONVERGENCE ZONE AXIS IS CENTERED ALONG 6N10W 7N15W 3N30W 1N40W INTO EXTREME NORTHERN BRAZIL NEAR 1N50W. SCATTERED MODERATE CONVECTION WITHIN 75 NM EITHER SIDE OF THE ITCZ AXIS E OF 30W. ...DISCUSSION... GULF OF MEXICO... THE HIGH PRES SYSTEM THAT MOVED ACROSS THE LOWER MISSISSIPPI VALLEY THE 24 HOURS HAS NOW RETREATED NORTHEAST INTO THE EASTERN OHIO VALLEY. AS A RESULT...THE PRES GRADIENT OVER THE EASTERN GULF HAS SLACKENED CONSIDERABLY AND THE STRONG NORTHERLY WINDS BEHIND THE COLD FRONT THAT PASSED THROUGH THE EASTERN GULF AND FLORIDA SAT HAVE DIMINISHED TO LESS THAN 20 KT S OF 28N ACCORDING TO SURFACE OBSERVATIONS AND THE 0328 UTC ASCAT PASS. THE SOUTHERN STREAM UPPER JET...WITH WESTERLY WINDS NEAR 100 KT...LIES OVER THE GULF ALONG 26N. THIS JET IS TRANSPORTING MID TO UPPER LEVEL TROPICAL MOISTURE EASTWARD ACROSS THE GULF. MULTILAYERED CLOUDINESS CAN BE FOUND OVER MUCH OF THE GULF. OVER THE WESTERN GULF...WINDS HAVE ALREADY BEGUN TO TURN EASTERLY TO SOUTHEASTERLY ON THE SW SIDE OF THIS HIGH PRES CENTER. THESE SOUTHERLY WINDS ARE FOUND WELL INTO THE SOUTHERN PLAINS AND ARE FEEDING INTO A LOW PRES SYSTEM CURRENTLY TRAVERSING THE ROCKIES. SATELLITE-BASED TOTAL PRECIPITABLE WATER IMAGERY REVEALS THAT THIS SOUTHERLY RETURN FLOW IS ALREADY INCREASING THE LOW TO MID LEVEL AVAILABLE MOISTURE IN THE WESTERN GULF. INFRARED IMAGERY AND RADAR CONFIRM SHOWER ACTIVITY OVER THE SE RIO GRANDE VALLEY AT THE MOMENT. THE GREATEST CHANCE OF SHOWER ACTIVITY IS EXPECTED OVER THE NW GULF TODAY AND WILL SHIFT EASTWARD INTO THE CENTRAL GULF MON AS THE LOW PRES SYSTEM IN THE ROCKIES MOVES EAST AND DRAGS A WEAK SURFACE BOUNDARY WITH IT INTO THE MISSISSIPPI VALLEY. CARIBBEAN SEA... THE TRADE WINDS OVER THE CARIBBEAN HAVE WEAKENED DUE TO THE SLACKENING PRES GRADIENT BETWEEN CLIMATOLOGICAL LOW PRES OVER NORTHERN COLOMBIA AND THE RIDGE EXTENDING FROM A 1024 MB HIGH NEAR 31N50N TO THE NW CARIBBEAN NEAR 20N80W. THE 0144 UTC ASCAT CONFIRMS THIS...WITH 20 TO 25 KT EASTERLY TRADEWINDS NOW CONFINED TO NEAR THE COAST OF NORTHERN COLOMBIA. THE RIDGE N OF THE AREA HAS SHIFTED EASTWARD DUE TO THE PROGRESSION OF THE COLD FRONT THAT MOVED THROUGH FLORIDA SAT AND INTO THE SW N ATLANTIC. THE SOUTHERN EDGE OF THIS FRONT HAS MOVED INTO THE NW CARIBBEAN...BRINGING SHOWERS NEAR THE FRONT AND 20 TO 25 KT N WINDS N OF THE FRONT ACCORDING TO THE 0326 ASCAT PASS. THE FRONT HAS STALLED OVER THE NW CARIBBEAN AND WILL DISSIPATE LATER TODAY. ELSEWHERE...THE CARIBBEAN CONTINUES TO BE MARKED BY STRONG SUBSIDENCE AND LIMITED MOISTURE...BRINGING TRANQUIL WEATHER TO MUCH OF THE AREA. SCATTERED SHOWERS ARE PRIMARILY LIMITED TO THE EASTERN CARIBBEAN E OF 70W AND THE CENTRAL CARIBBEAN N OF 15N BETWEEN 70W AND 75W AT THIS TIME. ATLANTIC OCEAN... A COLD FRONT LIES OVER THE SW N ATLANTIC FROM 31N71W TO 27N77W AND STATIONARY TO 23N801W. RECENT OBSERVATIONS SHOW THE N WINDS HAVE DIMINISHED TO 15 KT OR LESS N OF THE BAHAMAS AND W OF THE COLD FRONT. SCATTERED SHOWERS LIE WITHIN 120 NM E OF THE COLD FRONT AT THE MOMENT AND THUNDERSTORMS NOW ARE LIMITED TO THE AREA AHEAD OF THIS FRONT N OF 30N. THE DEEP LAYER LOW SUPPORTING THIS FRONTAL BOUNDARY IS LIFTING NORTHEAST OFF THE NEW ENGLAND COAST THIS MORNING AND THE UPPER LEVEL TROUGHING OVER THE SW N ATLANTIC WILL QUICKLY BE REPLACED BY WESTWARD BUILDING RIDGING FROM THE CENTRAL ATLANTIC ACROSS THE BAHAMAS. AS A RESULT...THE COLD FRONT WILL ADVANCE EASTWARD THROUGH THE NORTHERN PORTION OF THE FORECAST AREA BUT WILL STALL BETWEEN SOUTH FLORIDA AND THE BAHAMAS TODAY BEFORE BEGINNING TO LIFT NORTH AS A WEAK WARM FRONT BY MON. THE ADVANCING COLD FRONT HAS ALREADY SHIFTED THE SURFACE RIDGE FARTHER EAST OVER THE PAST 24 HOURS...WITH THE RIDGE NOW EXTENDING FROM 1024 MB HIGH NEAR 31N50N TO THE NW CARIBBEAN NEAR 20N80W. THIS RIDGING IS EXPECTED TO WEAKEN FURTHER AND SHIFT SOUTHWARD AS THE ADVANCING PORTION OF THE COLD FRONT ENCROACHES UPON IT. TO THE WEST OF THIS RIDGE LIES A POSITIVELY TILTED UPPER TROUGH THAT WILL PINCH OFF AN UPPER LOW OVER THE AZORES OVER THE NEXT FEW DAYS. A 100 KT WEST-SOUTHWESTERLY UPPER JET LIES ON THE LEADING EDGE OF THIS TROUGH AND IS TRANSPORTING TROPICAL MOISTURE ALOFT NORTHEASTWARD TOWARD WEST AFRICA...WITH MAINLY CLOUDY SKIES FOUND ALONG THE ROUTE FROM THE FRENCH GUIANA TO CAPE VERDE ISLANDS AS A RESULT. UPPER LEVEL DIFFLUENCE IN THE JET EXIT REGION IS CURRENTLY SUPPORTING SCATTERED MODERATE SHOWERS AND THUNDERSTORMS ALONG THE ITCZ AXIS E OF 30W. $$ SCHAUER