000 AXNT20 KNHC 241755 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT SEP 24 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 1715 UTC. ...SPECIAL FEATURES... TROPICAL STORM OPHELIA IS CENTERED NEAR 17.8N 56.0W AT 24/1500 UTC OR ABOUT 335 NM E OF THE LEEWARD ISLANDS MOVING NW AT 11 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. PLEASE SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS. CONVECTION HAS BEGUN TO REDEVELOP NEAR THE CENTER OF OPHELIA. CURRENTLY NUMEROUS STRONG CONVECTION IS FROM 16N-17N BETWEEN 52W-54W...AND FROM 17N-21N BETWEEN 52W-56W. SCATTERED MODERATE/STRONG CONVECTION IS FROM 12N-14N BETWEEN 53W-56W...AND FROM 16N-21N BETWEEN 56W-58W. TROPICAL DEPRESSION SEVENTEEN IS CENTERED NEAR 11.0N 26.7W AT 24/1500 UTC...OR ABOUT 265 NM SSW OF THE SOUTHERNMOST CAPE VERDE ISLANDS MOVING WNW NEAR 14 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PLEASE SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. SCATTERED MODERATE/STRONG CONVECTION IS AROUND THE WRN SEMI-CIRCLE FROM 8N-13N BETWEEN 26W-29W. A SURFACE TROUGH E OF THE FLORIDA PENINSULA ALONG 30N78W TO 25N78W IS PRODUCING A LARGE AREA OF SHOWERS/THUNDERSTORMS ACROSS THE BAHAMAS. NUMEROUS SHOWERS/THUNDERSTORMS ARE FROM 21N-25N BETWEEN 75W-78W. SCATTERED SHOWERS/THUNDERSTORMS ARE N OF 25N BETWEEN 76W-79W. THIS AREA HAS BECOME A LITTLE BETTER ORGANIZED OVER THE PAST SEVERAL HOURS AND SOME ADDITIONAL ORGANIZATION IS POSSIBLE OVER THE NEXT DAY OR SO AS THE SYSTEM MOVES NWD. ...TROPICAL WAVES... TROPICAL WAVE IS IN THE CENTRAL ATLC ALONG 20N38W TO 12N39W MOVING W 10-15 KT. VISIBLE SATELLITE IMAGERY ALONG WITH AN ASCAT SCATTEROMETER FROM 1240 UTC SHOWS CYCLONIC SURFACE FLOW AROUND THE WAVE AXIS. TOTAL PRECIPITABLE WATER IMAGERY ALSO INDICATES THE WAVE LIES AHEAD OF A SURGE OF DEEP LAYER MOISTURE. CURRENTLY NO DEEP CONVECTION ACCOMPANIES THE WAVE. ...ITCZ/MONSOON TROUGH... DUE TO THE CIRCULATION OF T.D. SEVENTEEN...THE MONSOON TROUGH HAS BROKEN DOWN WITH ONLY PORTIONS OVER AFRICA REMAINING. AS T.D. SEVENTEEN MOVES TOWARDS THE WEST...THE MONSOON TROUGH WILL BUILD BACK IN BEHIND IT. ...DISCUSSION... GULF OF MEXICO... AS OF 1500 UTC...A WEAK STATIONARY FRONT EXTENDS ACROSS THE NRN GULF OF MEXICO FROM N CENTRAL FLORIDA NEAR TALLAHASSEE TO S OF LOUISIANA ALONG 31N84W TO 29N91W. THE FRONT IS SUPPORTED BY A LONGWAVE UPPER LEVEL TROUGH THAT COVERS THE ERN CONUS. DRY AIR ALOFT IS SINKING DOWN INTO THE AREA WHICH IS LIMITING SHOWER ACTIVITY ALONG THE FRONT. A SURFACE TROUGH EXTENDS S OF THE FRONTAL BOUNDARY ALONG 27N85W TO 23N91W SUPPORTING ISOLATED SHOWERS WITHIN 100 NM OF THE AXIS. A FEW ISOLATED SHOWERS HAVE ALSO FORMED OVER SW FLORIDA AND ARE MOVING EWD. WEAK UPPER RIDGING COVERS THE SE GULF EXTENDING FROM THE YUCATAN PENINSULA. EXPECT THE FRONTAL BOUNDARY TO REMAIN STATIONARY AND BEGIN TO WEAKEN. THE UPPER LEVEL TROUGH WILL ALSO REMAIN SOMEWHAT STATIONARY ACROSS THE ERN CONUS KEEPING DRY AIR ACROSS THE NW GULF WHICH WILL SUPPORT FAIR CONDITIONS. CARIBBEAN SEA... UPPER LEVEL RIDGING COVERS THE WRN CARIBBEAN AROUND AN AXIS OVER THE YUCATAN PENINSULA AND A SECOND AXIS OVER THE SW CARIBBEAN. AN UPPER LEVEL TROUGH COVERS THE ERN CARIBBEAN ACCOMPANIED BY DRY AIR. TOTAL PRECIPITABLE WATER IMAGERY INDICATES AN AREA OF MOISTURE OVER THE WRN CARIBBEAN WHICH IS HELPING SUPPORT SCATTERED SHOWERS/THUNDERSTORMS FROM 12N-18N BETWEEN 78W-85W. SHOWERS/THUNDERSTORMS ARE ALSO S OF 12N INFLUENCED BY THE MONSOON TROUGH THAT EXTENDS FROM SRN COSTA RICA TO NRN COLOMBIA. THE ERN CARIBBEAN IS UNDER MOSTLY FAIR CONDITIONS DUE TO THE AFOREMENTIONED DRY ALOFT ALONG WITH 15-20 KT ELY TRADEWIND FLOW. TROPICAL STORM OPHELIA IS CURRENTLY E OF THE NRN LEEWARD ISLANDS AND IS EXPECTED TO MOVE N OF THE CARIBBEAN. SOME OF THE MOISTURE TO THE S OF THE SYSTEM MAY STILL MAKE ITS WAY INTO THE ERN CARIBBEAN. ATLANTIC OCEAN... A SURFACE TROUGH E OF THE FLORIDA PENINSULA IS PRODUCING A LARGE AREA OF SHOWERS/THUNDERSTORMS ACROSS THE SW N ATLC INCLUDING MUCH OF THE BAHAMAS. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS. ALOFT...AN UPPER LEVEL TROUGH OVER THE ERN CONUS EXTENDS SLIGHTLY OVER THE WRN ATLC WITH AN UPPER LEVEL RIDGE TO THE E CENTERED NEAR 34N66W. THIS UPPER RIDGE IS SUPPORTING A SURFACE RIDGE AROUND A 1026 MB HIGH NEAR 33N61W SUPPORTING FAIR WEATHER. AN UPPER LEVEL LOW IS TO THE S NEAR 22N67W. THIS UPPER LEVEL LOW/TROUGH CONTINUES TO HELP SHEAR T.S. OPHELIA. ANOTHER LONGWAVE UPPER TROUGH COVERS THE ERN ATLC SUPPORTING A COLD FRONT THAT CLIPS THE AREA ALONG 32N32W TO 30N38W SUPPORTING ISOLATED SHOWERS WITHIN 100 NM OF THE AXIS. A WEAK 1021 MB HIGH IS E OF THE FRONT NEAR THE MADEIRA ISLANDS PROVIDING FAIR WEATHER ACROSS THE SE ATLC. A BROAD UPPER LEVEL RIDGE COVERS THE TROPICAL ATLC CENTERED NEAR 16N34W. T.S. OPHELIA WILL CONTINUE TO MOVE NW WHILE T.D. SEVENTEEN WILL MOVE WWD. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON