000 AXNT20 KNHC 031755 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT SEP 03 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. ...SPECIAL FEATURES... TROPICAL STORM LEE IS NEARLY STATIONARY CENTERED NEAR 29.3N 91.8W AT 03/1800 UTC OR ABOUT 39 NM SW OF MORGAN CITY LOUISIANA AND ABOUT 56 NM S OF LAFAYETTE LOUISIANA. ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB. MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT. DOPPLER RADAR AND LIGHTNING DATA INDICATE A BROAD BAND OF NUMEROUS MODERATE AND ISOLATED STRONG CONVECTION FOCUSED ON THE EASTERN SEMI-CIRCLE OF THE STORM BETWEEN 83W-92W N OF 23N TO INLAND OVER SE LOUISIANA...SOUTHERN MISSISSIPPI...EXTREME SOUTHWESTERN ALABAMA...AND THE FAR WESTERN FLORIDA PANHANDLE. SIMILAR CONVECTION IS AROUND THE LOW LEVEL CIRCULATION AFFECTING THE EASTERN COASTAL WATERS OF TEXAS INTO THE WESTERN LOUISIANA COAST E OF 94W. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/WTNT33 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 230 MILES FROM THE CENTER. A STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 3 TO 5 FEET ABOVE GROUND LEVEL ALONG THE LOUISIANA COAST...AND BY AS MUCH AS 2 TO 4 FEET ABOVE GROUND LEVEL ALONG THE MISSISSIPPI AND ALABAMA COASTS INCLUDING MOBILE BAY. HURRICANE KATIA IS CENTERED NEAR 19.6N 55.8W AT 03/1500 UTC OR ABOUT 485 MI...785 KM ENE OF THE NORTHERN LEEWARD ISLANDS MOVING NW AT 9 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 989 MB. MAXIMUM SUSTAINED WIND SPEED IS 65 KT WITH GUSTS TO 80 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM 17N TO 23N BETWEEN 52W-59W. HURRICANE-FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM...FROM THE CENTER...AND TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 175 MILES...280 KM. A GENERAL NW MOTION IS EXPECTED TO CONTINUE THROUGH MONDAY WITH KATIA REMAINING WELL NORTH OF THE LEEWARD ISLANDS. HOWEVER...WELLS GENERATED BY KATIA ARE AFFECTING THE LESSER ANTILLES AND COULD BEGIN TO AFFECT BERMUDA BY TONIGHT OR SUNDAY. THESE SWELLS ARE LIKELY TO CAUSE LIFE-THREATENING SURF AND RIP CURRENT CONDITIONS. ...TROPICAL WAVE... TROPICAL WAVE IS ANALYZED FROM 21N33W TO A 1010 MB LOW ON THE SOUTHERN EXTENT OF THE WAVE NEAR 11N33W MOVING W-NW 10-15 KT. THIS SYSTEM IN EMBEDDED IN A SURGE OF DEEP MOISTURE NOTICED ON WATER VAPOR IMAGERY. HOWEVER...AN UPPER LEVEL ANTI-CYCLONIC CIRCULATION IS TO THE NW OF THIS FEATURE PROVIDING MID-UPPER LEVEL SUBSIDENCE AND THEREFORE THE CONVECTION IS LIMITED TO A FEW ISOLATED SHOWERS AND THUNDERSTORMS IN THE VICINITY OF THE WAVE AXIS N OF 13N. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS INLAND ACROSS WEST AFRICA...ENTERING THE ATLC OCEAN THROUGH THE COAST OF SENEGAL NEAR 14N17W ALONG 11N20W TO 12N24W. THE BROAD CYCLONIC WIND FIELD ASSOCIATED TO THE TROPICAL WAVE HAS BECOME MORE APPARENT OVER THE PAST 6 HOURS. ALSO...SURFACE RIDGING AXIS OVER THE FAR E ATLC WAS ABLE TO CUT THROUGH THE MONSOON TROUGH. THESE TWO FEATURES MADE THE OCEANIC MONSOON TROUGH TO BREAK AND WEAKEN. THEREFORE...THE MONSOON TROUGH AXIS PREVIOUSLY ANALYZED ALONG THE SOUTHERN EXTENSION OF THE TROPICAL WAVE HAS BEEN REMOVED. THE BROAD CYCLONIC FIELD ONLY ALLOWS FOR A SMALL PORTION OF THE ITCZ TO DEVELOP FROM 6N40W TO 5N50W. SCATTERED MODERATE CONVECTION IS FROM 8N TO 12N BETWEEN 17W AND 24W. ISOLATED MODERATE CONVECTION IS WITHIN 90 NM ON EITHER SIDE OF THE ITCZ. ...DISCUSSION... GULF OF MEXICO... THE MAIN AREA OF INTEREST IN THE GULF IS TROPICAL STORM LEE IMPACTING THE WATERS ALONG NORTHERN GULF COAST STATES BETWEEN 83W-94W. FOR MORE INFORMATION PLEASE SEE SPECIAL FEATURES ABOVE. CARIBBEAN SEA... MOSTLY FAIR WEATHER CONDITIONS ARE NOTED ACROSS THE CARIBBEAN THIS AFTERNOON ON VISIBLE SATELLITE IMAGERY...ESPECIALLY ACROSS THE EASTERN BASIN E OF 70W...WHERE WATER VAPOR IMAGERY SHOWS THE GREATEST MID-UPPER LEVEL DRYNESS. OBSERVATIONS ACROSS THE BASIN SHOW 10-15 KT EASTERLY TRADES WITH A FEW ISOLATED LOW TOP SHOWERS E OF 77W. THIS FLOW TURNS SOUTHERLY W OF 77W IN RESPONSE TO THE BROAD LOWER PRESSURE FIELD ASSOCIATED TO TROPICAL STORM LEE. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE DEVELOPING ALONG THE COASTAL WATERS OF COSTA RICA AND NICARAGUA WITHIN 50-120 NM...IN CLOSE PROXIMITY TO THE MONSOON TROUGH INLAND OVER CENTRAL AMERICA. ATLANTIC OCEAN... THE MAIN AREA OF INTEREST IN THE ATLANTIC OCEAN IS HURRICANE KATIA DESCRIBED IN THE SPECIAL FEATURES SECTION ABOVE. WATER VAPOR IMAGERY INDICATES A MID-UPPER LEVEL TROUGH/LOW LOCATED OVER THE SW NORTH ATLC. THIS FEATURE IS SUPPORTING A WEAK SURFACE TROUGH EXTENDING SW ALONG 31N68W TO 27N76W. ISOLATED SHOWERS ARE WITHIN 25 NM EITHER SIDE OF THE SURFACE TROUGH. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE TO THE ESE OF THIS SURFACE TROUGH N OF 25N BETWEEN 60W-69W. THIS IS DUE TO LOW LEVEL MOISTURE CONVERGENCE AND MID/UPPER LEVEL LIFT ASSOCIATED TO THE UPPER TROUGH. THE REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE OF A BROAD SURFACE RIDGE...ANCHORED BY A 1025 MB HIGH CENTERED NEAR 33N41W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GARCIA