000 AXNT20 KNHC 171743 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON SEP 17 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1735 UTC. ...SPECIAL FEATURES... TROPICAL STORM NADINE IS CENTERED NEAR 32.9N 35.3W AT 17/1500 UTC OR ABOUT 585 MI...940 KM SW OF THE AZORES MOVING NE AT 15 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 987 MB. MAXIMUM SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SCATTERED WEAK TO MODERATE CONVECTION IS FROM 31N-37N BETWEEN 29W-39W. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. ...TROPICAL WAVES... TROPICAL WAVE MOVES ACROSS THE CENTRAL TROPICAL ATLC WITH AXIS EXTENDING FROM 16N33W TO 10N37W MOVING W AT 10-15 KT. THIS WAVE IS EMBEDDED WITHIN BROAD CYCLONIC FLOW AND ALIGNS WITH A SURGE OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. HOWEVER...THIS WAVE IS EMBEDDED IN DRY SAHARAN AIR ALOFT...ALLOWING FOR ONLY A FEW ISOLATED SHOWERS IN THE VICINITY OF THE WAVE AXIS. TROPICAL WAVE APPROACHES THE LESSER ANTILLES ANALYZED FROM 18N56W TO 11N60W MOVING W AT 5-10 KT. A 1011 MB SURFACE LOW IS EMBEDDED ALONG THE WAVE AXIS NEAR 14N59W. THE WAVE LIES WITHIN AN AREA OF MAXIMUM MOISTURE EVIDENT IN TOTAL PRECIPITABLE WATER IMAGERY. THE WAVE REMAINS VERY SHALLOW AND EXHIBITS A LACK OF SIGNIFICANT DEEP CONVECTION WITH GLOBAL MODEL DATA INDICATING A 700 MB TROUGH AXIS FARTHER TO THE WEST OF THE WAVE AXIS ACROSS THE EASTERN CARIBBEAN SEA. THEREFORE...THE CONVECTION ASSOCIATED TO THIS SYSTEM IS AFFECTING THE ERN CARIBBEAN AND LESSER ANTILLES FROM BARBADOS TO BARBUDA BETWEEN 59W-68W. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS IS ANALYZED FROM THE WEST AFRICAN COAST OF GUINEA NEAR 10N14W ALONG 8N20W 10N30W 9N40W TO 10N46W. SCATTERED WEAK TO MODERATE CONVECTION IS FROM 6N-10N BETWEEN 43W-47W...AS WELL AS FROM 3N-10N BETWEEN 26W AND THE COAST OF WEST AFRICA. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY INDICATES A VIGOROUS MIDDLE TO UPPER LEVEL TROUGH MOVING ACROSS THE FAR NW GULF. THIS FEATURE SUPPORTS A 1006 MB LOW CENTERED NEAR 28N93W WITH A SURFACE TROUGH EXTENDING SSW FROM THE LOW CENTER ALONG 25N95W TO NEAR 22N97W. DESPITE THE LOCATION OF THE SURFACE LOW AND TROUGH...SCATTERED MODERATE TO HEAVY SHOWERS AND THUNDERSTORMS ARE DISPLACED E OF THE SURFACE FEATURES OVER THE COASTAL WATERS OF MISSISSIPPI AND EASTERN LOUISIANA N OF 26N BETWEEN 87W-92W...WHERE MUCH OF THE LIFTING DYNAMICS ASSOCIATED TO UPPER DIFFLUENCE IS LOCATED. ISOLATED SHOWERS AND THUNDERSTORMS ARE ALSO WITHIN 100 NM E OF THE SURFACE TROUGH. MOIST SOUTHERLY LOW-LEVEL FLOW IS ELSEWHERE ACROSS THE ERN HALF OF THE GULF WITH A FEW LINES OF SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS N OF 25N E OF 90W. COMPUTER MODELS SUGGEST THE SURFACE LOW WILL MOVE NE OUT OF OUR DISCUSSION AREA TONIGHT AND BECOME EMBEDDED WITHIN THE NEXT COLD FRONT TO SWEEP FROM THE CENTRAL PLAINS INTO THE SE CONUS BY EARLY TUESDAY. HOWEVER...WHILE STRONG SUBSIDENCE TAKES OVER THE W AND NW BASINS...THE WEATHER ACROSS MUCH OF THE ERN HALF OF THE GULF AND BAY OF CAMPECHE WILL REMAIN UNSETTLED AS SURFACE TROUGHING LINGERS IN THIS REGION OVER THE NEXT 24-48 HOURS. CARIBBEAN SEA... THE MAIN REGION OF INTEREST REMAINS OVER THE ERN CARIBBEAN AS A TROPICAL WAVE AND ASSOCIATED LOW PRESSURE SYSTEM SLOWLY TAKE OVER THE LESSER ANTILLES PRODUCING SCATTERED HEAVY SHOWERS AND ISOLATED THUNDERSTORMS OVER THIS GROUP OF ISLANDS AND PARTS OF THE ERN CARIBBEAN FROM BARBADOS TO BARBUDA BETWEEN 59W-68W. WHILE SURFACE TROUGHING REMAINS E OF THE ANTILLES WHERE THE WAVE AND SURFACE LOW ARE LOCATED...MIDDLE TROUGHING IS NOTED ON MODEL DATA AT 700 MB COVERING MUCH OF THE ERN CARIBBEAN E OF 68W. THE OVERALL ACTIVITY WILL SLOWLY MOVE W ACROSS THE NRN ANTILLES AND ERN CARIBBEAN DURING THE NEXT 24 HOURS. SCATTERED MODERATE SHOWERS ARE NOTED WITHIN 50-80 NM OFF THE COAST OF PANAMA... COSTA RICA...AND SRN NICARAGUA ASSOCIATED TO THE ERN PACIFIC MONSOON TROUGH EXTENDING ACROSS CENTRAL AMERICA TO NRN COLOMBIA. THE REMAINDER OF THE DISCUSSION AREA IS UNDER FAIR WEATHER CONDITIONS RELATED TO DRY AIR AND MODERATE TO STRONG SUBSIDENCE ALOFT...SUPPRESSING DEEP CONVECTION AND ONLY ALLOWING FOR A FEW ISOLATED SHOWERS OVER THE NW BASIN. ATLANTIC OCEAN... A WEAK UPPER LEVEL TROUGH MOVING ACROSS THE FAR ERN GULF OF MEXICO IS GENERATING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE NW BAHAMAS TO THE COAST OF THE FLORIDA PENINSULA AND STRAITS S OF 27N W OF 77W. THIS AREA OF SHOWERS IS EXPECTED TO LIFT N DROWN BY A FRONTAL SYSTEM MOVING FROM THE CENTRAL PLAINS TO THE SE CONUS DURING THE NEXT 24 HOURS. AN UPPER LEVEL LONGWAVE/TROUGH IS NOTED ON WATER VAPOR IMAGERY MOVING INTO THE N-CENTRAL ATLC ALONG 50W N OF THE DISCUSSION AREA. THIS FEATURE SUPPORTS A COLD FRONT EXTENDING INTO OUR AREA AS A WEAK SURFACE TROUGH ALONG 31N56W TO NEAR 24N62W. THIS BOUNDARY IS MOSTLY EMBEDDED WITH DRY AIR KEEPING SHOWER ACTIVITY AT A MINIMUM. CURRENTLY...ISOLATED WEAK SHOWERS ARE NOTED WITHIN 20 NM E OF THE AXIS. THIS BOUNDARY IS EXPECTED TO WEAKEN AND DISSIPATE DURING THE NEXT 24 HOURS...AS HIGH PRESSURE CONTINUES TO BUILD OVER THE WRN ATLC THROUGH EARLY TUESDAY. TROPICAL STORM NADINE IS APPROACHING THE ERN ATLC WATERS NEAR THE AZORES. SEE SPECIAL FEATURE ABOVE FOR MORE DETAILS ON NADINE. A WEAK AREA OF LOW-LEVEL CONVERGENCE IS NOTED S OF NADINE ANALYZED FROM 28N34W TO 23N49W WITH VERY LITTLE ACTIVITY. OTHERWISE...THE REMAINDER OF THE ATLC BASIN DISCUSSION AREA IS DOMINATED BY WEAK SURFACE RIDGING AROUND A 1018 MB HIGH NEAR 26N23W. THE OVERALL FAIR WEATHER IS ENHANCED ALOFT BY THICK LAYER OF SAHARAN DUST NOTED ON METEOSAT-9 SAL PRODUCT E OF 40W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GARCIA