000 AXNT20 KNHC 181755 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SUN SEP 18 2011 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1745 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST OF GUINEA BISSAU NEAR 12N16W TO A 1011 MB LOW NEAR 11N24W TO A SECOND 1009 MB LOW NEAR 11N35W ENDING NEAR 8N47W. THE MONSOON TROUGH HAS BECOME THE DOMINANT FEATURE ACROSS THE TROPICAL ATLC OVER THE PAST 6-8 HOURS...LEADING TO A WEAKENING OF THE INTER-TROPICAL CONVERGENCE ZONE. THE LARGE AND STRETCHED OUT MONSOON GYRE IS PRODUCING WIDELY SCATTERED MODERATE TO ISOLATED STRONG CONVECTION FROM 4N-14N E OF 47W. ...DISCUSSION... GULF OF MEXICO... SATELLITE VISIBLE IMAGERY SHOWS MOSTLY CLEAR SKIES WITH A FEW ISOLATED WEAK SHOWERS MOVING ALONG WITH THE LIGHT ANTICYCLONIC FLOW PRESENT ACROSS THE BASIN. WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL TROUGH/SHORT WAVE MOVING EASTWARD ACROSS SOUTHERN TEXAS...SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MOVING ALONG THE TEXAS COAST UP TO 70 NM OFFSHORE. COMPUTER MODELS SUGGEST SIMILAR ACTIVITY LINGERING OVER THE FAR NW BASIN OVER THE NEXT 24 HOURS. DOPPLER RADAR IMAGERY INDICATES A CLUSTER OF SHOWERS AND ISOLATED THUNDERSTORMS MOVING WESTWARD ACROSS THE FLORIDA STRAITS E OF 83W. AN INCREASE IN CONVECTION OVER THIS REGION IS EXPECTED AS A SURFACE TROUGH CROSSES THE FLORIDA PENINSULA INTO THE EASTERN GULF THIS AFTERNOON. CARIBBEAN SEA... MODERATE TO HIGH SURFACE MOISTURE VALUES ARE NOTED ON TOTAL PRECIPITABLE WATER IMAGERY W OF 80W. WHILE SCATTERED SHOWERS ROAM THIS AREA...STRONGER ACTIVITY FOCUSES OVER THE YUCATAN CHANNEL AND THE COASTAL WATERS NEAR EASTERN HONDURAS... NICARAGUA...COSTA RICA...PANAMA...AND COLOMBIA UP TO 100 NM OFFSHORE W OF 75W. MOST OF THE ACTIVITY S OF 12N W OF 75W IS ALSO ENHANCED BY THE MONSOON TROUGH ANALYZED OVER THE FAR SW BASIN EXTENDING ACROSS COSTA RICA INTO NORTHERN COLOMBIA. THIS AREA OF CONVECTION IS MOVING INLAND OVER CENTRAL AMERICA...WITH THE ACTIVITY EXPECTED TO CONTINUE TO IMPACT THE REGION OVER THE NEXT 24 HOURS. WATER VAPOR IMAGERY SHOWS A BROAD UPPER LEVEL CYCLONIC CIRCULATION OVER PUERTO RICO. WITH PLENTY OF LOW LEVEL MOISTURE IN ITS SURROUNDINGS...THIS FEATURE IS PROVIDING MID TO UPPER LEVEL LIFT AND INSTABILITY TO GENERATE AN AREA OF SCATTERED MODERATE TO STRONG CONVECTION AFFECTING THE FAR NE CARIBBEAN N OF 13N E OF 68W INCLUDING THE LESSER ANTILLES. THIS SYSTEM IS EXPECTED TO DRIFT WWD WHICH SHOULD INCREASE THE SHOWER ACTIVITY OVER THE CENTRAL PORTION OF THE BASIN. THE REMAINDER OF THE BASIN REMAINS UNDER FAIR WEATHER CONDITIONS. ATLANTIC OCEAN... AN UPPER LEVEL TROUGH MOVES OFF THE EASTERN CONUS SEABOARD THIS AFTERNOON...SUPPORTING A FRONTAL BOUNDARY THAT ENTERS OUR DISCUSSION AREA AS STATIONARY NEAR 32N76W EXTENDING SW TO THE FLORIDA COAST NEAR DAYTONA BEACH. LOW-LEVEL CONVERGENCE AND UPPER DIVERGENCE IN THE VICINITY OF THE FRONT IS GENERATING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 30 NM ON EITHER SIDE OF THE FRONT. TO THE S OF THIS BOUNDARY...A SURFACE TROUGH MOVES ACROSS THE NORTHERN BAHAMAS ANALYZED FROM 29N77W TO 23N80W. THE ACTIVITY ASSOCIATED TO THIS SYSTEM IS AFFECTING THE COASTAL WATERS OF CUBA S OF 25N W OF 77W...AND SOME OF THIS ACTIVITY IS MOVING WESTWARD INTO THE FLORIDA STRAITS. A BROAD UPPER LEVEL CYCLONIC CIRCULATION IS SPINNING OVER THE ISLAND OF PUERTO RICO. WITH PLENTY OF LOW LEVEL MOISTURE IN ITS SURROUNDINGS...THIS FEATURE IS PROVIDING MID TO UPPER LEVEL LIFT AND INSTABILITY TO GENERATE AN AREA OF SCATTERED MODERATE TO STRONG CONVECTION S OF 26N BETWEEN 60W-68W. FARTHER E...A 1010 MB LOW/TROUGH SYSTEM IS CENTERED NEAR 17N45W PRODUCING AN AREA OF DISORGANIZED SHOWERS AND THUNDERSTORMS FROM 15N-20N BETWEEN 40W-45W. THIS SYSTEM WILL CONTINUE TO SLOWLY MOVE WESTWARD OVER THE NEXT 24 HOURS WITH VERY LOW CHANCES TO BECOME A TROPICAL STORM. TO THE N OF THIS LOW PRESSURE SYSTEM...AN UPPER LEVEL LOW CENTERED SW OF THE AZORES SUPPORTS A WEAK LOW PRESSURE SYSTEM AND ASSOCIATED TROUGH WITH A NARROW LINE OF ISOLATED SHOWERS EXTENDING ALONG THE BOUNDARY FROM 32N37W TO 27N40W TO 26N45W. THE REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE OF A WEAK BROAD SURFACE RIDGE N OF THE AREA. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GARCIA