000 AXNT20 KNHC 212338 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST WED NOV 21 2012 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF GUINEA AT 10N14W TO 7N18W. THE ITCZ BEGINS AT 7N18W AND CONTINUES ALONG 4N27W 4N39W 6N47W. A SURFACE TROUGH IS EMBEDDED WITHIN THE ITCZ ALONG 12N47W TO 6N47W. SCATTERED MODERATE/STRONG CONVECTION IS FROM 4N-7N BETWEEN 14W-17W. WIDELY ISOLATED MODERATE CONVECTION IS NORTH OF THE ITCZ AXIS FROM 6N-11N BETWEEN 24W-42W. MOST OF THIS ACTIVITY IS ENHANCED BY DIFFLUENCE ALOFT AROUND AN UPPER LEVEL TROUGH WITH AXIS FROM 21N34W TO 7N48W. ...DISCUSSION... GULF OF MEXICO... MAINLY ZONAL WESTERLY FLOW COVERS THE GULF OF MEXICO ALONG WITH DRY AIR WHICH IS HELPING PROVIDE FAIR CONDITIONS ACROSS THE MAJORITY OF THE BASIN. A SHORTWAVE UPPER TROUGH SINKS SLIGHTLY INTO THE NE CORNER OF THE GULF DRAWING ANOTHER SURGE OF COOL AND DRY AIR SOUTHWARD. AT THE SURFACE...RIDGING CONTINUES ACROSS THE BASIN WITH AXIS EXTENDING FROM A HIGH CENTER OVER ARKANSAS TO A SECOND HIGH CENTER OVER EASTERN MEXICO NEAR 24N99W. THIS PATTERN IS PROVIDING MAINLY NORTH TO NORTHEAST WINDS ACROSS THE BASIN RANGING FROM 10-20 KT. A FEW ISOLATED SHOWERS ARE IN THE FAR SW GULF NEAR A SURFACE TROUGH ALONG 23N97W TO 19N95W WHICH IS REALLY DEPICTING AN AREA OF CONVERGENCE. SURFACE RIDGING IS EXPECTED TO REMAIN ACROSS THE BASIN FOR THE NEXT SEVERAL DAYS. CARIBBEAN SEA... A BROAD UPPER LEVEL RIDGE COVERS THE CARIBBEAN WITH MAINLY DRY WESTERLY FLOW OVER THE NW CORNER AND THE EASTERN PORTIONS WHILE MOIST SOUTHWESTERLY FLOW COVERS THE CENTRAL CARIBBEAN. THE COMBINATION OF MOIST SOUTHWESTERLY FLOW ALOFT AND NORTHEASTERLY SURFACE WINDS EXPERIENCING SPEED CONVERGENCE AT THE SURFACE IS HELPING ENHANCE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ACROSS THE SW CARIBBEAN SOUTH OF 13N BETWEEN 73W-84W COVERING MUCH OF COSTA RICA AND PANAMA. THE MONSOON TROUGH ACROSS BOTH COUNTRIES MAY ALSO BE PLAYING A ROLE IN THE ACTIVITY PROVIDING STRONGER SURFACE CONFLUENCE IN THAT AREA. A FEW WIDELY ISOLATED SHOWERS CONTINUE TO THE NORTH WITH ACTIVITY PRESENT OVER JAMAICA AND HISPANIOLA. A WEAK SURFACE TROUGH IS ANALYZED IN THE EASTERN CARIBBEAN FROM THE VIRGIN ISLANDS TO NEAR 13N70W. ISOLATED SHOWERS ARE WITHIN 60 NM EITHER SIDE OF THE AXIS. LITTLE CHANGE IS EXPECTED OVER THE NEXT SEVERAL DAYS. ATLANTIC OCEAN... A NARROW UPPER LEVEL TROUGH EXTENDS DOWN THE EASTERN SEABOARD INTO NORTHERN FLORIDA SUPPORTING A SLIGHTLY COMPLICATED PATTERN AT THE SURFACE OVER THE SW NORTH ATLC. A 1007 MB SPOT SURFACE LOW IS CENTERED NEAR 27N71W WITH A SURFACE TROUGH EXTENDING FROM THE CENTER TO NEAR 24N72W. A SECOND SURFACE TROUGH IS NORTH OF THIS AREA EXTENDING FROM A SECOND SURFACE LOW TO THE NE NEAR 34N57W. THIS SECOND SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR 31N62W CONTINUING ALONG 30N70W 28N78W. SCATTERED SHOWERS ARE NORTH OF THE AXIS BETWEEN 67W-78W. ONLY A FEW WIDELY ISOLATED SHOWERS ARE ELSEWHERE DUE TO THE PRESENCE OF STRONG DRY AIR ALONG IN MAINLY ZONAL WESTERLY FLOW. A SECOND SHORTWAVE UPPER TROUGH IS MOVING INTO THE CENTRAL ATLC ALONG 35N49W TO 25N45W SUPPORTING A COLD FRONT THAT ENTERS THE AREA NEAR 32N50W TO 20N65W. ONLY A FEW ISOLATED SHOWERS ARE ALONG THE FRONTAL BOUNDARY. MORE SCATTERED ACTIVITY IS FARTHER EAST NEAR THE AREA OF DIFFLUENCE ALOFT AROUND THE UPPER TROUGH AXIS. ANOTHER UPPER TROUGH AXIS IS OVER THE TROPICAL EAST ATLC ALONG 21N34W TO 7N48W PROVIDING A LARGE AREA OF DIFFLUENCE ALOFT ACROSS THIS AREA. IT IS HELPING SUPPORT CONVECTION NEAR AND NORTH OF THE ITCZ AXIS AS WELL AS SOME ISOLATED SHOWERS FARTHER NORTH FROM 11N-18N BETWEEN 23W-38W. AN UPPER LEVEL RIDGE ACROSS THE NE ATLC SUPPORTS A 1025 MB HIGH NEAR 35N21W WHICH IS PROVIDING SURFACE RIDGING ACROSS THE EASTERN ATLC PROVIDING FAIR WEATHER BESIDES NEAR WHERE THE UPPER TROUGH IS CAUSING SOME SHOWER ACTIVITY. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON