000 AXNT20 KNHC 021827 AAA TWDAT TROPICAL WEATHER DISCUSSION...UPDATED NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI SEP 02 2011 UPDATED SPECIAL FEATURES 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 1715 UTC. ...SPECIAL FEATURES... THE CENTER OF UPGRADED HURRICANE KATIA AT 02/1500 UTC IS NEAR 17.5N 52.4W OR ABOUT 705 MI E OF THE NORTHERN LEEWARD ISLANDS MOVING WNW OR 300 DEGREES AT 12 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB. MAXIMUM SUSTAINED WIND SPEED IS 65 KT WITH GUSTS TO 80 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCPAT2/WTNT32 KNHC FOR FULL DETAILS. NUMEROUS MODERATE TO STRONG CONVECTION IS FROM 16N-23N BETWEEN 47W-55W. THE CENTER OF UPGRADED TROPICAL STORM LEE AT 02/1800 UTC IS NEAR 27.4N 91.5W OR 200 MI SE OF CAMERON LOUISIANA OR ABOUT 210 MI SW OF THE MOUTH OF THE MISSISSIPPI RIVER MOVING NW OR 325 DEGREES AT 2 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCPAT3/ WTNT33 KNHC FOR FULL DETAILS. NUMEROUS MODERATE TO STRONG CONVECTION IS WITHIN 240 NM IN THE SE SEMICIRCLE EXCEPT 180 NM IN THE NE QUADRANT OF LEE. VERY HEAVY RAINFALL WILL OCCUR ALONG THE NORTHERN GULF COAST AS DESCRIBED IN MORE DETAIL IN THE GULF OF MEXICO SECTION BELOW. 1006 MB LOW PRES IS NEAR 38N63W OR ABOUT 460 MI S-SE OF HALIFAX NOVA SCOTIA MOVING NE AROUND 10 KT. CONVECTION REMAINS SHEARED AND REMOVED OFF TO THE NE OF THE LOW CENTER AND ENVIRONMENTAL CONDITIONS ARE BECOMING UNFAVORABLE FOR A TROPICAL CYCLONE TO DEVELOP. THUS THIS LOW NOW HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. ...TROPICAL WAVES... TROPICAL WAVE IN THE ATLANTIC OCEAN FROM 17N28W TO 1012 MB LOW PRES NEAR 10N30W MOVING WNW AROUND 15 KT. SCATTERED MODERATE CONVECTION IS WITHIN 180-240 NM IN THE W QUADRANT OF THE LOW WITH ONLY SCATTERED SHOWERS EVIDENT ELSEWHERE WITHIN 120-180 NM W OF THE TROPICAL WAVE AXIS. THIS WAVE IS COINCIDENT WITH A MOISTURE MAXIMUM INDICATED BY TOTAL PRECIPITABLE WATER SATELLITE IMAGERY. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM 13N25W TO 07N37W TO 09N42W THEN RESUMES IN THE CENTRAL CARIBBEAN SEA NEAR THE COAST OF COLOMBIA NEAR 12N71W TO THE COSTA RICA/HONDURAS BORDER NEAR 11N84W. NO INTERTROPICAL CONVERGENCE ZONE AXIS IS EVIDENT IN THE ATLANTIC OCEAN. SCATTERED TO NUMEROUS MODERATE TO STRONG CONVECTION IS WITHIN 120 NM EITHER SIDE OF THE MONSOON TROUGH W OF 74W. ...DISCUSSION... GULF OF MEXICO... THE MAIN AREA OF INTEREST IN THE GULF IS RECENTLY UPGRADED TROPICAL STORM LEE AS DESCRIBED ABOVE IN THE SPECIAL FEATURES SECTION. EXPERIMENTAL NHC RAINFALL GRAPHICS FORECAST MAXIMUM RAINFALL AMOUNTS OVER 15 INCHES IN SE LOUISIANA DURING THE NEXT 24 HOURS. THE LATEST HPC FORECAST IS 10-15 INCHES OVER SOUTHERN LOUISIANA...SOUTHERN MISSISSIPPI AND SOUTHERN ALABAMA THROUGH SUNDAY WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 20 INCHES. THESE RAINS ARE EXPECTED TO CAUSE EXTENSIVE FLOODING... ESPECIALLY IN URBAN AREAS. TROPICAL STORM FORCE WINDS ARE EXPECTED TO REACH LAND IN THE TROPICAL STORM WARNING AREA IN THE LATE AFTERNOON OR EVENING. A STORM SURGE OF 2-4 FT ABOVE GROUND LEVEL IS EXPECTED ALONG THE NORTHERN GULF COAST IN AREAS OF ONSHORE FLOW...AND DANGEROUS RIP CURRENTS ARE ALSO LIKELY ALONG THE NORTHERN GULF COAST. ISOLATED TORNADOES AREA POSSIBLE OVER PORTIONS OF SOUTHERN LOUISIANA TONIGHT. REFER TO FLOOD PRODUCTS AND HURRICANE LOCAL STATEMENTS ISSUED BY LOCAL NWS FORECAST OFFICES FOR MORE DETAILED INFORMATION ON THESE THREATS. THE HEAVY RAINFALL WILL ALSO DIMINISH VISIBILITIES BELOW 5 NM OVER THE N CENTRAL GULF CREATING AN ADDITIONAL HAZARD FOR MARINERS. CARIBBEAN SEA... A 1114 UTC WINDSAT SCATTEROMETER PASS CAPTURED NE-E 15-20 KT WINDS OVER THE CENTRAL CARIBBEAN PRODUCING SEAS TO 8 FT NEAR THE COAST OF COLOMBIA. THESE STRONGER WINDS ARE DUE TO A TIGHT PRES GRADIENT BETWEEN AN ABNORMALLY NORTHWARD MONSOON TROUGH IN THE SW CARIBBEAN AND RIDGING NE OF THE AREA. WINDS ARE EXPECTED TO DIMINISH TO 5-15 KT ACROSS THE BASIN THIS WEEKEND AS THE REGION WILL BE UNDER WEAK FLOW CAUGHT BETWEEN HURRICANE KATIA NE OF THE AREA AND TROPICAL STORM LEE NW OF THE AREA. THE DIMINISHING WINDS WILL ALSO ALLOW FOR SEAS TO SUBSIDE TO 2-4 FT ACROSS THE MAJORITY OF THE BASIN THIS WEEKEND...LOCALLY TO 5 FT NEAR THE COAST OF COLOMBIA. ATLANTIC OCEAN... THE MAIN AREA OF INTEREST IN THE ATLANTIC OCEAN IS HURRICANE KATIA AS DESCRIBED IN THE SPECIAL FEATURES SECTION ABOVE. OTHER THAN THE CONVECTION DESCRIBED ABOVE...SCATTERED MODERATE CONVECTION IS FROM 06N-10N E OF 23W WHERE SW MONSOONAL FLOW IS CONVERGING NEAR THE COAST OF AFRICA. A NEARLY STATIONARY 1025 MB AREA OF HIGH PRES IS CENTERED JUST N OF THE AREA NEAR 33N39W WITH BROAD RIDGING AND MAINLY FAIR WEATHER IN PLACE OVER THE AREA N OF 26N E OF 60W. A CONVERGENCE AXIS EXTENDS FROM NEAR BERMUDA TO THE S-SW NEAR 25N69W. SCATTERED MODERATE CONVECTION IS OCCURRING WITHIN 120-180 NM E OF THIS FEATURE. A SURFACE TROUGH EXTENDS FROM 1011 MB CENTERED NEAR 32N68W TO 29N77W. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING WITHIN 60-90 NM EITHER SIDE OF THIS TROUGH. THIS TROUGH WILL LINGER IN THE SW N ATLANTIC THROUGH SAT DISSIPATING ON SUN. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ LEWITSKY