000 AXNT20 KNHC 201749 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 33W S OF 17N MOVING W NEAR 12 KT. THE WAVE RESIDES IN AN AREA OF DEEP LAYER MOISTURE ACROSS THE ERN ATLC AS OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. CIMSS WAVETRAK MODEL GUIDANCE INDICATES A MAXIMUM IN 850 MB RELATIVE VORTICITY IN THE VICINITY OF THE WAVE AXIS BUT THIS RELATIVE VORTICITY STRETCHES FROM NE OF A 1012 MB LOW NEAR 16N46W EWD TO 24W NEAR THE CAPE VERDE ISLANDS. THEREFORE...A HIGH LEVEL OF UNCERTAINTY IS PLACED IN THE POSITION OF THE WAVE AT THIS TIME AND IS BASED MORE ON EXTRAPOLATION. NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 8N13W 6N20W 8N30W 11N35W 12N41W 11N49W 10N62W. WIDELY SCATTERED MODERATE CONVECTION IS FROM 4N-8N BETWEEN 13W-22W. ...DISCUSSION... GULF OF MEXICO... AS OF 1500 UTC...A SURFACE TROUGH EXTENDS ACROSS THE SE GULF FROM 27N83W TO THE YUCATAN PENINSULA NEAR 22N87W. ISOLATED SHOWERS AND TSTMS ARE WITHIN 90 NM EITHER SIDE OF THE TROUGH AXIS. THIS ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL TROUGH OVER THE NE GULF WITH AXIS ALONG 86W AND AN UPPER LEVEL RIDGE OVER THE SE GULF CENTERED OVER THE STRAITS OF FLORIDA NEAR 24N80W. ACROSS THE SW GULF...ISOLATED SHOWERS AND TSTMS ARE S OF 24N W OF 90W IN ASSOCIATION WITH UPPER LEVEL DIFFLUENCE CAUSED BY AN UPPER LEVEL RIDGE W OF 89W. THIS UPPER LEVEL RIDGE IS ANCHORED OVER W/CENTRAL MEXICO NEAR 20N105W. OTHERWISE...THE GULF REMAINS UNDER LIGHT ELY SURFACE FLOW THIS AFTERNOON. CARIBBEAN SEA... AN UPPER LEVEL TROUGH EXTENDS ACROSS THE GULF OF HONDURAS AND THE NW CARIBBEAN. LOW-LEVEL CONVERGENCE AND LIFT PROVIDED BY THE UPPER TROUGH IS GENERATING SCATTERED SHOWERS AND TSTMS FROM 19N-22N BETWEEN 82W-88W. SCATTERED SHOWER ACTIVITY EXTENDS FARTHER SOUTH FROM 15N-19N BETWEEN 80W-89W. ACROSS THE SW CARIBBEAN...AN UPPER LEVEL DIFFLUENT ENVIRONMENT IS IN PLACE DUE TO UPPER LEVEL TROUGHING ACROSS THE E PACIFIC AND UPPER LEVEL RIDGING OVER NRN SOUTH AMERICA. STRONG SLY DIFFLUENT FLOW OVER PANAMA AND THE SW CARIBBEAN IS SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS SW OF A LINE FROM 13N84W TO 9N76W. ELSEWHERE ACROSS THE REMAINDER OF THE CARIBBEAN...PRIMARILY E OF 74W... UPPER LEVEL TROUGHING EXTENDS OVER THE BASIN FROM AN UPPER LEVEL LOW CENTERED OVER THE CENTRAL ATLC NEAR 25N59W. CONDITIONS REMAIN GENERALLY FAIR UNDER THE INFLUENCE OF DRY AIR ALOFT AS NOTED ON WATER VAPOR IMAGERY. HOWEVER...A FEW ISOLATED SHOWERS ARE OCCURRING ACROSS PORTIONS OF HISPANIOLA...PUERTO RICO AND THE US/UK VIRGIN ISLANDS DUE TO THE MAIN AXIS OF CYCLONIC CURVATURE LOCATED ALOFT OVER THE ERN MOST GREATER ANTILLES. FARTHER TO THE SE...A FEW PASSING ISOLATED SHOWERS ARE NOTED ON SATELLITE IMAGERY ACROSS THE WINDWARD ISLANDS THIS AFTERNOON. ATLANTIC OCEAN... A FEW ISOLATED SHOWERS ARE ACROSS THE FAR WRN ATLC N OF 24N W OF 78W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN AN UPPER LEVEL RIDGE EXTENDING FROM THE FLORIDA STRAITS OVER THE NW BAHAMAS TO 27N73W AND AN UPPER LEVEL SHORTWAVE TROUGH ACROSS THE NE GULF. THE UPPER LEVEL SHORTWAVE TROUGH LINKS UP WITH A LARGER UPPER LEVEL TROUGH ACROSS THE NW ATLC...N OF THE DISCUSSION AREA...AND THIS TROUGH SUPPORTS A COLD FRONT THAT ENTERS THE AREA NEAR 32N65W EXTENDING ALONG 31N TO 80W. A PRE-FRONTAL TROUGH IS ANALYZED FROM 31N70W THROUGH A 1015 MB LOW NEAR 28N71W TO NEAR 25N72W. SCATTERED SHOWERS AND TSTMS ARE S OF THE COLD FRONT AND COVER THE AREA FROM 29N-33N BETWEEN 60W-72W. FARTHER TO THE SE...ANOTHER WEAKER SURFACE TROUGH EXTENDS FROM 22N62W TO 27N61W. SCATTERED SHOWERS ARE WITHIN 120 NM EITHER SIDE OF THE TROUGH AXIS. THIS TROUGH IS SUPPORTED BY AN UPPER LEVEL LOW NEAR 25N59W. SCATTERED SHOWERS ARE ALSO N OF THE WINDWARD ISLANDS FROM 18N-21N BETWEEN 60W-66W IN ASSOCIATION WITH THE UPPER LOW. A 1012 MB SURFACE LOW IS CENTERED NEAR 16N46W WITH SCATTERED SHOWERS AND ISOLATED TSTMS COVERING THE AREA NE OF THE LOW CENTER FROM 15N-22N BETWEEN 37W-45W. ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES ANCHORED BY A 1026 MB HIGH NEAR 33N41W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS N OF 25N BETWEEN 34W-43W. AN UPPER LEVEL LOW DOMINATES THE NE ATLC CENTERED NEAR 30N27W. MOIST SWLY UPPER LEVEL FLOW IS E OF 28W ACROSS THE ERN ATLC AND IS GENERATING POSSIBLE ISOLATED SHOWERS FROM THE CAPE VERDE ISLANDS TO NE OF THE CANARY ISLANDS. $$ HUFFMAN