000 AXNT20 KNHC 211742 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT SEP 21 2013 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. ...TROPICAL WAVES... TROPICAL WAVE EXTENDS FROM 12N22W TO 18N22W MOVING W AT 10-15 KT. THE WAVE REMAINS EMBEDDED WITHIN THE MONSOON TROUGH AND COINCIDES WITH A WEAK SURFACE TO 700 MB TROUGH AND 700 MB RELATIVE VORTICITY MAXIMUM IN THE VICINITY OF 15N23W ALONG THE WAVE AXIS. WIDELY SCATTERED MODERATE CONVECTION IS FROM 11N-16N BETWEEN 20W-27W AND IS LIKELY MORE ASSOCIATED WITH UPPER LEVEL DIFFLUENCE ON THE EASTERN PERIPHERY OF AN UPPER LEVEL TROUGH AXIS EXTENDING FROM 25N30W TO 15N40W. TROPICAL WAVE EXTENDS FROM 16N38W TO 25N37W MOVING W AT 10-15 KT. TOTAL PRECIPITABLE WATER IMAGERY INDICATES MOST OF THE WAVE HAS FRACTURED AWAY FROM THE MOISTURE-LADEN MONSOON TROUGH REGION AND IS EXPECTED TO BEGIN INTERACTION WITH A FRONTAL TROUGH TO THE NW OVER THE NEXT FEW DAYS. NO SIGNIFICANT DEEP CONVECTION IS NOTED ON SATELLITE IMAGERY AT THIS TIME WITH THE WAVE. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 14N17W TO 11N23W TO A 1012 MB LOW NEAR 13N33W TO 12N35W TO 13N38W TO 12N40W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 12N40W TO 05N53W. SCATTERED MODERATE CONVECTION IS FROM 14N-18N BETWEEN 27W-33W. ISOLATED MODERATE CONVECTION IS FROM 06N-16N BETWEEN 17W-28W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY INDICATES A PROGRESSIVE AND VIGOROUS UPPER LEVEL TROUGH EXTENDS FROM THE GREAT LAKES REGION SOUTH- SOUTHWESTWARD OVER THE MID-MISSISSIPPI RIVER VALLEY TO A BASE OVER SOUTHERN TEXAS NEAR 27N100W. THIS TROUGHING ALOFT SUPPORTS A COLD FRONT ANALYZED FROM SW LOUISIANA NEAR 30N93W SW TO 27N95W THEN INLAND NEAR BROWNSVILLE TEXAS AND INLAND ACROSS NORTHERN MEXICO. MOIST LOW-LEVEL SOUTHERLY RETURN FLOW IS NOTED ACROSS MUCH OF THE GULF BASIN THIS AFTERNOON LEADING TO GENERATE SCATTERED SHOWERS AND WIDELY SCATTERED TSTMS NW OF A LINE FROM THE FLORIDA PANHANDLE NEAR 30N85W TO THE EAST-CENTRAL COAST OF MEXICO NEAR 21N98W. MOST OF THE CONVECTION WELL TO THE SOUTHEAST OF THE COLD FRONT IS CONTINUING TO BE ENHANCED BY AN UPPER LEVEL DIFFLUENT ENVIRONMENT DUE TO AN UPPER LEVEL ANTICYCLONE CENTERED NEAR 26N93W. OTHERWISE SOUTHEASTERN PORTIONS OF THE GULF... INCLUDING THE FLORIDA PENINSULA REMAIN UNDER MOSTLY FAIR SKIES THIS AFTERNOON WITH SE TO S WINDS IN THE RANGE OF 10 TO 20 KT. LOOKING AHEAD...THE NORTHERN PORTION OF THE COLD FRONT IS FORECAST TO SWEEP ACROSS THE COASTAL PLAINS WITH THE TAIL END OF THE FRONT REMAINING STATIONARY OVER WESTERN WATERS THROUGH MONDAY. CARIBBEAN SEA... AN UPPER LEVEL TROUGH AXIS EXTENDS INTO THE NW CARIBBEAN FROM THE SW NORTH ATLC NEAR 23N76W TO A BASE NEAR 16N88W. WHILE AN OVERALL WEAK SURFACE PRESSURE GRADIENT IS NOTED ACROSS THE CARIBBEAN BASIN...THE MIDDLE TO UPPER LEVEL DYNAMICS ASSOCIATED WITH THIS TROUGHING IS GENERATING SCATTERED SHOWERS AND WIDELY SCATTERED TSTMS FROM 15N-20N BETWEEN 76W-87W. OTHERWISE...A NARROW UPPER LEVEL RIDGE AXIS EXTENDS FROM OVER THE SW CARIBBEAN NEAR 12N79W NORTHEASTWARD TO 17N68W PROVIDING OVERALL CLEAR SKIES AND FAIR CONDITIONS THIS AFTERNOON. FINALLY...OVER THE EASTERN CARIBBEAN...UPPER LEVEL FLOW RESUMES AS SOUTHERLY WITH MOISTURE ADVECTING FROM OFF THE NORTH-CENTRAL COAST OF VENEZUELA TO THE LEEWARD ISLANDS PRIMARILY E OF 68W. MOST OF THIS MOISTURE IS NOTED ON SATELLITE IMAGERY AS MIDDLE TO UPPER LEVEL CLOUDINESS WITH A FEW ISOLATED SHOWERS EMBEDDED WITHIN EASTERLY TRADE WIND FLOW. LOOKING AHEAD...A SURFACE TROUGH IS ANALYZED EAST OF THE LESSER ANTILLES ALONG 56W AND IS EXPECTED TO BEGIN IMPACTING THE ISLANDS BY EARLY SUNDAY INTO MONDAY WITH INCREASED CLOUDINESS AND PRECIPITATION. HISPANIOLA... CURRENTLY SKIES REMAIN FAIR THIS AFTERNOON...HOWEVER WITH AN UPPER LEVEL DIFFLUENT ENVIRONMENT NOTED ON WATER VAPOR IMAGERY ACROSS THE ISLAND STRETCHING WESTWARD OVER THE WESTERN CARIBBEAN SEA...SCATTERED SHOWER AND TSTM ACTIVITY IS FORECAST TO INITIATE LATE THIS AFTERNOON AND CONTINUE THROUGH THE EVENING HOURS. THIS OVERALL SYNOPTIC PATTERN IS EXPECTED TO CHANGE LITTLE OVER THE NEXT FEW DAYS WITH AFTERNOON AND EARLY EVENING CONVECTION ANTICIPATED ACROSS THE ISLAND. ATLANTIC OCEAN... A MIDDLE TO UPPER LEVEL LOW IS CENTERED OVER THE WESTERN NORTH ATLC NEAR 36N71W THAT EXTENDS A TROUGH AXIS SOUTHWARD ALONG 71W TO 22N. THIS TROUGHING SUPPORTS AN OVERALL LOWER PRESSURE REGIME ACROSS THE SW NORTH ATLC WITH TWO SURFACE LOWS ANALYZED. THE FIRST LOW IS THE WEAKER OF THE TWO AS A 1010 MB LOW CENTERED NE OF THE BAHAMAS NEAR 26N74W. A SURFACE TROUGH EXTENDS SW FROM THE LOW CENTERED TO WEST OF ANDROS ISLAND NEAR 24N78W. WHILE THE OVERALL SURFACE FEATURE REMAINS WEAK...MIDDLE TO UPPER LEVEL DIFFLUENCE IS LARGELY RESPONSIBLE FOR WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS OCCURRING FROM 25N-33N BETWEEN 68W-74W. FARTHER EAST...A 1007 MB LOW IS CENTERED NEAR 29N62W AND EXHIBITS A STATIONARY FRONT ANALYZED INTO THE LOW FROM THE EAST ALONG 30N BETWEEN 48W-62W. SCATTERED SHOWERS AND WIDELY SCATTERED TSTMS ARE OCCURRING FROM 28N-33N BETWEEN 55W-61W IN THE VICINITY OF THE STATIONARY FRONT. A SURFACE TROUGH EXTENDS SW FROM THE LOW CENTER ALONG 25N63W TO 22N73W. LOW-LEVEL MOISTURE CONVERGENCE EAST OF THE SURFACE TROUGH AND AN OVERALL DIFFLUENT ENVIRONMENT ALOFT IS WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS FROM 22N-27N BETWEEN 55W-60W...AND FROM 20N-24N BETWEEN 60W-73W. TO THE SOUTHEAST...AN UPPER LEVEL ANTICYCLONE IS CENTERED NEAR 15N57W AND IS PROVIDING A FAVORABLE UPPER LEVEL DIFFLUENT ENVIRONMENT FOR A 1012 MB LOW CENTERED NEAR 13N56W. ISOLATED SHOWERS AND TSTMS ARE OCCURRING FROM 12N-16N BETWEEN 50W-59W. FINALLY...AN UPPER LEVEL TROUGH CONTINUES TO PROGRESS ACROSS THE NORTHERN CENTRAL ATLC WITH AXIS ALONG 39W THAT DIPS SOUTHWARD TO A BASE NEAR 36N. THIS TROUGHING SUPPORTS A COLD FRONT THAT EXTENDS FROM 36N36W TO 31N41W THEN CONTINUES AS A SURFACE TROUGH TO 27N51W. WIDELY SCATTERED SHOWERS AND TSTMS ARE OCCURRING PRIMARILY WITHIN 180 NM EAST OF THE COLD FRONT AND WITHIN 120 NM E-SE OF THE SURFACE TROUGH. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN