000 AXNT20 KNHC 130000 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED SEP 12 2012 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2345 UTC. ...SPECIAL FEATURE... TROPICAL STORM NADINE IS CENTERED NEAR 20.0N 48.9W 12/2100 UTC OR ABOUT 875 MI...1410 KM ENE OF THE LESSER ANTILLES MOVING NW AT 14 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB. MAXIMUM SUSTAINED WIND SPEED IS 55 KT WITH GUSTS TO 65 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. SCATTERED MODERATE TO STRONG CONVECTION IS FROM 16N-23N BETWEEN 45W-51W. ...TROPICAL WAVES... A TROPICAL WAVE AXIS IS ANALYZED FROM 16N33W TO A 1012 MB LOW LEVEL CENTER NEAR 9N31W MOVING W 10-15 KT. THIS SYSTEM IS EMBEDDED IN A SURGE OF MODERATE MOISTURE VALUES ON TOTAL PRECIPITABLE WATER IMAGERY. THIS SYSTEM IS ALSO EMBEDDED IN DRY SAHARAN AIR ALOFT LIMITING THE CONVECTIVE ACTIVITY NEAR THE CENTER. ONLY A SMALL AREA OF SCATTERED WEAK CONVECTION IS W OF THE LOW LEVEL CENTER. ...ITCZ/MONSOON TROUGH... THE OCEANIC MONSOON TROUGH AND ITCZ AXIS CONTINUE ARE DISRUPTED BY THE LARGE CYCLONIC WIND FIELD ASSOCIATED TO TROPICAL STORM NADINE AND A TROPICAL WAVE MOVING ACROSS THE CENTRAL TROPICAL ATLC. HOWEVER...SCATTERED SHOWERS AND THUNDERSTORMS ARE MOVING OFF THE COAST OF LIBERIA...SIERRA LEONE...AND GUINEA SPREADING UP TO 120 NM OFFSHORE. ...DISCUSSION... GULF OF MEXICO... A STATIONARY FRONT ENTERS THE ERN GULF THROUGH THE STRAITS OF FLORIDA...EXTENDING WNW ACROSS THE CENTRAL BASIN ALONG 26N90W TO THE COAST OF LOUISIANA NEAR 29N92W. THE ACTIVITY RELATED TO THIS FRONT IS WIDESPREAD ACROSS THE ERN AND NW BASINS...AS MOSAIC DOPPLER RADAR SHOWS SCATTERED SHOWERS AND THUNDERSTORMS BETWEEN 88W AND THE WRN COAST OF THE FLORIDA PENINSULA N OF THE STATIONARY FRONT...AS WELL AS N OF 26N BETWEEN THE FRONT AND THE COAST OF TEXAS. THE REASON FOR THE OVERALL ACTIVITY IS DUE TO AN UPPER LEVEL LOW NOTED ON WATER VAPOR IMAGERY CENTERED INLAND OVER NRN MISSISSIPPI AND EXTENDING AN UPPER LEVEL TROUGH AXIS S ACROSS THE CENTRAL BASIN TO THE YUCATAN PENINSULA. SIMILAR CONVECTION IS OVER THE WRN BAY OF CAMPECHE S OF 24N W OF 94W. MARINE OBSERVATIONS ACROSS THE GULF SHOW EASTERLY WINDS 10-15 KT ON THE ERN SIDE OF THE FRONT...AND S-EASTERLY WINDS 5-10 KT ON THE WRN SIDE OF THE FRONT. THE FRONT IS EXPECTED TO DRIFT N AS IT DISSIPATES DURING THE NEXT 24 HOURS. IN THE MEAN TIME...A SURFACE RIDGE OF HIGH PRESSURE WILL BUILD OVER THE NE BASIN. CARIBBEAN SEA... A STATIONARY FRONT EXTENDS N OF CUBA ACROSS THE STRAITS OF FLORIDA GENERATING SCATTERED SHOWERS INLAND W OF 80W...SOME OF THESE REACHING THE WATERS NEAR THE YUCATAN CHANNEL. OTHERWISE... A BROAD UPPER RIDGE CENTERED OVER THE NW BAHAMAS CONTINUES TO ADVECT DRY AIR ALOFT AND STRONG SUBSIDENCE ACROSS THE BASIN... SUPPRESSING DEEP CONVECTION AND ONLY ALLOWING FOR A FEW ISOLATED LOW-TOP SHOWERS DOTTING THE DISCUSSION AREA TONIGHT. HOWEVER... AN ELONGATED UPPER LOW DRIFTS WESTWARD CENTERED JUST A FEW MILES E OF PUERTO RICO. THIS UPPER FEATURE IS BRINGING MID TO UPPER LEVEL MOISTURE ACROSS THE NE AND N-CENTRAL BASIN AND THE LIFTING ASSOCIATED TO IT IS INCREASING THE POTENTIAL FOR MODERATE TO HEAVY SHOWERS IN THESE AREAS. LOW-MID LEVEL MOISTURE INCREASES OVER THE FAR SW BASIN ON TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE TO HEAVY SHOWERS ARE NOTED WITHIN 40-60 NM ACROSS THE COASTAL WATERS OF COLOMBIA...PANAMA...COSTA RICA AND SRN NICARAGUA. THE ACTIVITY IS ASSOCIATED TO THE ERN PACIFIC MONSOON TROUGH EXTENDING ACROSS INLAND PORTIONS OF CENTRAL AMERICA TO NRN COLOMBIA. FAIR WEATHER CONDITIONS WITH A FEW ISOLATED SHOWERS WILL PREDOMINATE ACROSS THE DISCUSSION AREA DURING THE NEXT 24 HOURS. MODERATE TO ISOLATED STRONG CONVECTION WILL LINGER OVER THE SW BASIN DURING THE FORECAST PERIOD. ATLANTIC OCEAN... AN UPPER LEVEL TROUGH CONTINUES TO MOVE ACROSS THE WRN NORTH ATLANTIC SUPPORTING A STATIONARY FRONT EXTENDING INTO OUR DISCUSSION AREA ALONG 30N59W 24N70W TO ACROSS THE BAHAMAS NEAR 24N76W AND INTO THE GULF OF MEXICO ACROSS THE STRAITS OF FLORIDA. SCATTERED MODERATE TO HEAVY SHOWERS AND THUNDERSTORMS ARE NOTED WITHIN 140 NM ON EITHER SIDE OF THE FRONT E OF 70W ...AND WITHIN 180 NM N OF THE FRONT W OF 70W. THE FRONT IS EXPECTED TO WEAKEN AND BEGIN DISSIPATION WITHIN THE NEXT 12-24 HOURS. TROPICAL STORM NADINE IS WELL TO THE ENE OF THE LESSER ANTILLES. SEE SPECIAL FEATURE ABOVE FOR MORE DETAILS ON NADINE. A BROAD OCCLUDED LOW PRESSURE SYSTEM IS CENTERED S OF THE AZORES NEAR 35N28W. A DISSIPATING COLD FRONT ASSOCIATED TO THIS LOW ENTERS OUR DISCUSSION AREA NEAR 30N22W ALONG 27N28W AND BACK OUT OF THE AREA ALONG 32N37W. THE CONVECTION RELATED TO THIS FRONT HAS DECREASED TO ALMOST NOTHING ON SATELLITE IMAGERY. THE REMAINDER OF THE ATLC BASIN DISCUSSION AREA IS DOMINATED BY A SURFACE RIDGE OF HIGH PRESSURE ANCHORED BY A 1022 MB HIGH NEAR 32N43W AND AN UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED NEAR 18N27W. THE OVERALL FAIR WEATHER IS ENHANCED ALOFT BY THICK LAYER OF SAHARAN DUST NOTED ON METEOSAT-9 SAL PRODUCT E OF 50W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GARCIA