000 AXNT20 KNHC 201149 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SUN SEP 20 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. ...SPECIAL FEATURES... A 1011 MB LOW IS CENTERED E OF THE WINDWARD ISLANDS NEAR 15N45W MOVING TO THE WNW NEAR 9 KT. SCATTERED MODERATE CONVECTION IS FROM 14N-16N BETWEEN 44W-49W. WHILE THE SYSTEM REMAINS POORLY ORGANIZED...IT HAS A MEDIUM CHANCE...30 TO 50 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HRS. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 32W/33W S OF 19N MOVING W NEAR 12 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY AS WELL AS A MAXIMUM IN 850 MB RELATIVE VORTICITY SEEN IN THE CIMSS WAVETRAK MODEL GUIDANCE. NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE. TROPICAL WAVE IS ALONG 96W S OF 20N MOVING W NEAR 10 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM IN THE E PACIFIC BASIN WHERE MOST OF THE WAVE AXIS LIES. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS S OF 21N BETWEEN 95W-98W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N15W 13N30W 16N43W 12N48W 10N63W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 15N-17N BETWEEN 39W-42W. ...DISCUSSION... GULF OF MEXICO... AS OF 0900 UTC...A SURFACE TROUGH EXTENDS ACROSS THE SE GULF FROM 27N83W TO THE YUCATAN PENINSULA NEAR 21N87W. ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 150 NM EITHER SIDE OF THE TROUGH AXIS. THIS ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN A SHORTWAVE UPPER LEVEL TROUGH OVER THE N CENTRAL GULF WITH AXIS ALONG 87W AND AN UPPER LEVEL RIDGE OVER THE SE GULF CENTERED OVER THE STRAIGHTS OF FLORIDA NEAR 24N80W. ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE SW GULF S OF 22S W OF 89W IN ASSOCIATION WITH UPPER LEVEL DIFFLUENCE BETWEEN THE SHORTWAVE UPPER TROUGH OVER THE CENTRAL GULF AND ANOTHER UPPER LEVEL RIDGE OVER THE WRN GULF CENTERED OVER MEXICO NEAR 21N103W. SCATTERED SHOWERS/THUNDERSTORMS IN THE FAR SW GULF ARE ALSO ENHANCED BY SURFACE CONVERGENCE NEAR THE TROPICAL WAVE ALONG 96W...SEE ABOVE. EXPECT A SURFACE RIDGE TO BUILD E TO W BY MON. CARIBBEAN SEA... AS OF 0900 UTC...A SURFACE TROUGH EXTENDS OVER THE NW CARIBBEAN FROM 19N84W TO 11N83W. ISOLATED SHOWERS/THUNDERSTORMS ARE FROM 14N-22N BETWEEN W OF 78W. THE ACTIVITY IS ENHANCED BY SURFACE CONVERGENCE NEAR THE TROUGH AS WELL AS UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE OVER THE SE GULF AND THE BAHAMAS CENTERED OVER THE STRAIGHTS OF FLORIDA NEAR 24N80W AND AN UPPER LEVEL INVERTED TROUGH OVER THE NW CARIBBEAN AND CENTRAL AMERICA. THE REMAINDER OF THE CENTRAL AND E CARIBBEAN REMAINS FAIRLY CALM UNDER THE INFLUENCE OF DRY AIR ALOFT. HOWEVER...A FEW ISOLATED SHOWERS/THUNDERSTORMS ARE S OF WRN HISPANIOLA FROM 17N-18N BETWEEN 71W-74W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN THE UPPER LEVEL RIDGE OVER THE BAHAMAS AND AN UPPER LEVEL LOW N OF THE WINDWARD ISLANDS NEAR 23N62W. ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS PUERTO RICO N OF 17N BETWEEN 66W-68W IN ASSOCIATION WITH THE AFOREMENTIONED UPPER LEVEL LOW N OF THE WINDWARD ISLANDS. FRESH TRADE WINDS ARE ACROSS THE SRN CARIBBEAN WITH THE STRONGEST NEAR THE COAST OF COLOMBIA. EXPECT SHOWERS/THUNDERSTORMS TO PERSIST OVER THE WRN CARIBBEAN AS THE UPPER LEVEL TROUGH OVER THE W CARIBBEAN MOVES W. ATLANTIC OCEAN... A FEW ISOLATED SHOWERS REMAIN ACROSS THE FAR WRN ATLC FROM 24N-29N W OF 78W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN AN UPPER LEVEL RIDGE OVER THE BAHAMAS CENTERED OVER THE STRAITS OF FLORIDA NEAR 24N80W AND A SHORTWAVE UPPER LEVEL TROUGH ACROSS THE N CENTRAL GULF. A 1014 MB SURFACE LOW IS NEAR 28N71W WITH A SURFACE TROUGH EXTENDING THROUGH IT FROM 31N70W TO 25N71W. SURFACE CONVERGENCE NEAR THE LOW AND TROUGH AXIS IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM 25N-28N BETWEEN 70W-72W. A SURFACE TROUGH EXTENDS FROM 26N58W TO 21N61W. ISOLATED SHOWERS ARE WITHIN 50 NM EITHER SIDE OF THE TROUGH AXIS. THE TROUGH IS SUPPORTED BY AN UPPER LEVEL LOW NEAR 23N62W. IS SHOWERS/THUNDERSTORMS ARE ALSO N OF THE WINDWARD ISLANDS FROM 18N-20N BETWEEN 62W-68W IN ASSOCIATION WITH THE UPPER LOW. ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES ANCHORED BY A 1025 MB HIGH NEAR 33N42W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS N OF 26N BETWEEN 34W-47W. AN UPPER LEVEL TROUGH DOMINATES THE E ATLC WITH AXIS ALONG 33N25W TO 23N35W. UPPER LEVEL DIFFLUENCE ON THE E SIDE OF THE TROUGH IS SUPPORTING ISOLATED SHOWERS FROM 23N-30N E OF 22W. A BROAD UPPER LEVEL RIDGE COVERS THE TROPICAL ATLC ENHANCING CONVECTION NEAR THE LOW CENTERED AT 15N45W. $$ WALTON