000 AXNT20 KNHC 240554 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 AM 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0445 UTC. ...SPECIAL FEATURES... TROPICAL STORM OPHELIA IS CENTERED NEAR 16.0N 54.5W AT 24/0300 UTC OR ABOUT 425 NM E OF THE LEEWARD ISLANDS MOVING WNW AT 12 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. OPHELIA IS IN A WEAKENING TREND AS IT IS BEING SHEARED. SCATTERED MODERATE/STRONG CONVECTION IS WELL REMOVED FROM THE LOW LEVEL CENTER WITHIN A 45 NM RADIUS OF 18N53W WITH SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVERING THE REMAINDER OF THE AREA FROM 15N-20N BETWEEN 48W-55W. A 1008 MB LOW IS S OF THE CAPE VERDE ISLANDS NEAR 10N23W EMBEDDED WITHIN THE MONSOON TROUGH. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 9N-11N BETWEEN 23W-26W. THIS SYSTEM CONTINUES TO BECOME BETTER ORGANIZED. ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR A TROPICAL DEPRESSION TO FORM LATER TODAY AND THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WEST-NORTHWESTWARD AT ABOUT 8 KT. ...TROPICAL WAVES... TROPICAL WAVE IS ANALYZED FROM 19N35W 12N37W TO 6N38W MOVING W AT 10-15 KT. WAVE IS WELL DEFINED IN THE UPPER LEVEL SATELLITE WINDS AND IN THE LOW CLOUDS ON SATELLITE IMAGERY. WAVE REMAINS EMBEDDED WITHIN DEEP LAYER MOISTURE AS SEEN ON THE TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED SHOWERS ARE WITHIN 75 NM EITHER SIDE OF THE WAVE AXIS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS AFRICA TO THE COAST NEAR 20N16W THEN RESUMES NEAR 12N17W THROUGH THE 1008 MB LOW IN THE SPECIAL FEATURES TO 8N32W. SMALL CLUSTERS OF SCATTERED MODERATE/ ISOLATED STRONG CONVECTION ARE FROM 5N-10N BETWEEN 29W-32W WITH LARGER CLUSTERS S OF OPHELIA FROM 10N-16N BETWEEN 46W-58W. ...DISCUSSION... GULF OF MEXICO... THE TAIL END OF A WEAKENING COLD FRONT EXTENDS INTO THE GULF ACROSS THE FLORIDA PANHANDLE NEAR PENSACOLA ALONG 28N87W TO 27N90W SUPPORTED BY AN UPPER TROUGH THAT COVERS THE MISSISSIPPI VALLEY AND THE E CONUS INTO THE GULF N OF 23N. HOWEVER...THE N GULF IS DOMINATED BY STRONG SUBSIDENCE AND DRY STABLE AIR THUS THE FRONT IS CURRENTLY PRODUCING ONLY WIDELY ISOLATED SHOWERS. AN UPPER RIDGE EXTENDS FROM THE E PACIFIC REGION ACROSS MEXICO COVERING THE SW GULF AND THE BAY OF CAMPECHE. A SURFACE TROUGH EXTENDS FROM THE E GULF NEAR 27N84W TO OVER THE YUCATAN PENINSULA NEAR 21N89W TO THE N BORDER OF GUATEMALA GENERATING SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS S OF 26N BETWEEN 83W-91W TO OVER THE YUCATAN PENINSULA AND INTO THE E BAY OF CAMPECHE. THE NW GULF IS UNDER REMARKABLY CLEAR SKIES TONIGHT. THE WEAK COLD FRONT WILL REACH FROM THE FLORIDA BIG BEND REGION TO THE CENTRAL GULF LATER THIS MORNING THEN STALL AND DISSIPATING THROUGH MON. HIGH PRESSURE WILL BUILD IN THE WAKE OF THE FRONT SUN THROUGH TUE AND SHIFT N WED. CARIBBEAN SEA... AN UPPER RIDGE COVERS THE SW CARIBBEAN S OF 18N W OF 70W WHILE AN UPPER TROUGH FROM THE CENTRAL ATLC COVERS THE E CARIBBEAN. EASTERLY WINDS COMBINED WITH THE DIFFLUENT ENVIRONMENT ALOFT OVER THE CENTRAL CARIBBEAN ARE GENERATING CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS MAINLY FROM 12N-18N W OF 73W TO OVER CENTRAL AMERICA AND IN THE GULF OF HONDURAS. THE MONSOON TROUGH EXTENDS ACROSS THE SW CARIBBEAN FROM COLOMBIA NEAR 9N76W ALONG 10N80W ACROSS COSTA RICA INTO THE E PACIFIC REGION NEAR 10N84W GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 12N BETWEEN 7W-84W. THIS IS LEAVING THE E CARIBBEAN UNDER CLEAR SKIES TONIGHT. TROPICAL STORM OPHELIA WILL CONTINUE TO MOVE NE OF THE LEEWARD ISLANDS SAT NIGHT THROUGH MON. ATLANTIC OCEAN... A SMALL UPPER RIDGE IS ANCHORED OVER THE FAR W ATLC NEAR THE CENTRAL BAHAMAS PROVIDING A DIFFLUENT ENVIRONMENT ALOFT WHILE A SURFACE TROUGH EXTENDS FROM 29N77W ACROSS GRAND BAHAMA ISLANDS TO THE N COAST OF CUBA NEAR 23N80W. HEAVY SHOWERS AND THUNDERSTORMS COVER THE S BAHAMA ISLANDS FROM 24N TO OVER CUBA BETWEEN 73W-77W WHILE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS COVER THE REMAINDER OF THE AREA S OF 30N BETWEEN 70W-81W. A BROAD UPPER RIDGE DOMINATES THE W ATLC ANCHORED ABOUT 150 NM NW OF BERMUDA PROVIDING DRY STABLE AIR OVER THE AREA N OF 25N BETWEEN 40W-70W. AN UPPER TROUGH EXTENDS FROM THE CENTRAL ATLC NEAR 23N63W OVER THE E CARIBBEAN BUT DUE TO THE DRY STABLE AIR IS NOT PRODUCING ANY SHOWER ACTIVITY. A BROAD SURFACE RIDGE DOMINATES THE REMAINDER OF THE ATLC N OF 20N ANCHORED BY A SERIES OF HIGHS N OF THE DISCUSSION AREA. THE SURFACE TROUGH WILL REMAIN NEARLY STATIONARY AND GRADUALLY DISSIPATE THROUGH SAT NIGHT. TROPICAL STORM OPHELIA WILL CONTINUE TO MOVE NE OF THE LEEWARD ISLANDS SAT NIGHT BEING N OF THE VIRGIN ISLANDS MON NIGHT BEFORE TURNING MORE NORTHWARD. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ PAW