000 AXNT20 KNHC 172354 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU SEP 17 2015 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 2315 UTC. ...SPECIAL FEATURES... TROPICAL DEPRESSION NINE IS CENTERED NEAR 16.5N 44.8W AT 17/2100 UTC OR ABOUT 955 NM E OF THE LESSER ANTILLES MOVING N AT 6 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND SPEED IS 25 KT WITH GUSTS TO 35 KT. ISOLATED MODERATE CONVECTION IS FROM 16N-20N BETWEEN 39W-45W. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. A 1008 MB LOW IS W-SW OF THE CAPE VERDE ISLANDS CENTERED NEAR 12N34W MOVING W-NW AT 10-15 KT. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR A TROPICAL DEPRESSION TO DEVELOP DURING THE NEXT DAY OR TWO WITH A HIGH CHANCE OF TROPICAL CYCLONE FORMATION OVER THE NEXT 48 HOURS. ISOLATED MODERATE CONVECTION COVERS A BROAD AREA SURROUNDING THE LOW FROM 06N-16N BETWEEN 25W-39W. ...TROPICAL WAVES... TROPICAL WAVE EXTENDS FROM 10N82W TO 17N82W MOVING W AT 20 KT. THE WAVE COINCIDES WITH 700 MB TROUGHING OVER THE SW CARIBBEAN SEA AND CENTRAL AMERICA BETWEEN 79W-86W. SCATTERED MODERATE CONVECTION IS FROM 05N-16N BETWEEN 77W-85W. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 13N17W TO 13N23W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 10N51W TO 09N61W. ASIDE FROM CONVECTION OCCURRING IN THE VICINITY OF THE SPECIAL FEATURES MENTIONED ABOVE...ISOLATED MODERATE CONVECTION IS FROM 10N-15N BETWEEN 20W-27W IN ASSOCIATION WITH A WEAK SURFACE TROUGH ANALYZED FROM 11N21W TO 15N24W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY SHOWS A STARK CONTRAST IN ATMOSPHERIC MOISTURE THIS EVENING DUE TO AN UPPER LEVEL TROUGH WITH AXIS EXTENDING FROM OVER THE WESTERN CAROLINAS NEAR 25N82W S-SW TO A BASE OVER THE EASTERN BAY OF CAMPECHE NEAR 19N91W. EAST OF THIS TROUGH AXIS...A 1011 MB LOW IS CENTERED NEAR 26N84W WITH A SURFACE TROUGH EXTENDING N TO 28N84W AND SW TO 23N88W. ANOTHER SURFACE TROUGH IS ANALYZED IN THE OFFSHORE SW NORTH ATLC WATERS OFF THE FLORIDA PENINSULA TO NEAR LAKE OKEECHOBEE TO NEAR 25N82W. BOTH BOUNDARIES AND THE LOW ARE PROVIDING FOCUS FOR NUMEROUS SHOWERS AND SCATTERED TSTMS EAST OF A LINE FROM THE FLORIDA BIG BEND REGION NEAR 30N84W TO THE NORTH-CENTRAL TIP OF THE YUCATAN PENINSULA NEAR 22N88W. OTHERWISE...EAST OF THE UPPER LEVEL TROUGH AXIS AND WEST OF THE PRIMARY WEATHER-PRODUCING SURFACE FEATURES...MOSTLY CLEAR SKIES PREVAIL. WATER VAPOR IMAGERY INDICATES VERY DRY AND SUBSIDENT CONDITIONS ALOFT DUE TO NORTHERLY FLOW ON THE EASTERN PERIPHERY OF AN UPPER LEVEL RIDGE ANCHORED OVER NORTHERN MEXICO NEAR 28N103W. THE OVERALL STABLE CONDITIONS ALOFT CONTINUE TO SUPPORT A SURFACE RIDGE AXIS EXTENDING FROM THE MISSISSIPPI RIVER VALLEY SW TO EAST-CENTRAL MEXICO. THE LOW IN THE EASTERN GULF WILL GRADUALLY DRIFT NORTHEASTWARD THROUGH LATE SATURDAY AND INTO THE SW NORTH ATLC REGION BY EARLY SUNDAY. CARIBBEAN SEA... AN UPPER LEVEL RIDGE IS CENTERED OVER THE WESTERN CARIBBEAN NEAR 17N83W PROVIDING MOSTLY DRY CONDITIONS ALOFT WITH THE EXCEPTION OF THE COASTAL NICARAGUA AND VICINITY. PRIMARILY THE RESULT OF A TROPICAL WAVE ALONG 82W...INCREASED CLOUDINESS...SCATTERED SHOWERS AND TSTMS ARE OCCURRING S OF 17N BETWEEN 79W-85W. IN ADDITION...THE MONSOON TROUGH AXIS EXTENDING ALONG 10N/11N BETWEEN NORTHERN COLOMBIA AND SOUTHERN COSTA RICA PROVIDING ADDITIONAL LOW-LEVEL MOISTURE CONVERGENCE DYNAMICS. NORTH OF THIS RIDGING...LATE AFTERNOON AND EARLY EVENING SCATTERED SHOWERS AND TSTMS ARE OCCURRING ACROSS CUBA AND JAMAICA. THIS ACTIVITY IS LIKELY DUE TO PEAK DAYTIME HEATING AND INSTABILITY AND IS EXPECTED TO DIMINISH GRADUALLY THROUGH THE OVERNIGHT HOURS. TO THE EAST OF THE RIDGE...AN UPPER LEVEL LOW IS CENTERED NEAR 18N72W. MOST MOISTURE ASSOCIATED WITH THE LOW IS NOTED IN THE FORM OF SCATTERED SHOWERS AND ISOLATED TSTMS ACROSS HISPANIOLA AND PUERTO RICO...INCLUDING THE ADJACENT COASTAL WATERS N OF 16N BETWEEN 64W-73W. OTHERWISE...MODERATE TO FRESH TRADES PREVAIL WITH OCCASIONAL STRONG BREEZE CONDITIONS OCCURRING WITHIN CLOSE PROXIMITY TO THE COAST OF NE COLOMBIA AND NW VENEZUELA. ...HISPANIOLA... AN UPPER LEVEL LOW IS CENTERED OVER EASTERN HISPANIOLA NEAR 18N72W PROVIDING INCREASED MOISTURE...CLOUDINESS...AND SCATTERED SHOWERS AND ISOLATED TSTMS ACROSS THE ISLAND AND ADJACENT COASTAL WATERS. WITH THE UPPER LEVEL FEATURE FORECAST TO SLOWLY MOVE SOUTHWARD THROUGH SUNDAY...INCREASED PROBABILITY OF SCATTERED AFTERNOON AND EVENING SHOWERS AND TSTMS ARE EXPECTED THROUGH THE UPCOMING WEEKEND. ATLANTIC OCEAN... WITH AN UPPER LEVEL TROUGH AXIS EXTENDING FROM OVER THE WESTERN CAROLINAS S-SW TO THE SW GULF OF MEXICO...MIDDLE TO UPPER LEVEL DIFFLUENCE IS MAXIMIZED OVER MUCH OF THE SW NORTH ATLC THIS EVENING DUE TO SOUTHWESTERLY FLOW BETWEEN THE TROUGHING AND AN UPPER LEVEL RIDGE ANCHORED NEAR 27N73W. NUMEROUS SHOWERS AND SCATTERED TSTMS ARE OCCURRING N OF 25N W OF 70W. FARTHER EAST... AN UPPER LEVEL TROUGH IS NOTED OVER THE CENTRAL NORTH ATLC WITH SHORTWAVE ENERGY LOCATED IN THE VICINITY OF 28N57W. THE TROUGHING SUPPORTS A COLD FRONT EXTENDING FROM 24N44W TO 30N52W AND A SURFACE TROUGH EXTENDING FROM THE COLD FRONT NEAR 31N50W TO 27N51W. ISOLATED SHOWERS ARE OCCURRING WITHIN 60 NM EITHER SIDE OF THE COLD FRONT AND SURFACE TROUGH BOUNDARIES. FINALLY... A WEAKENING COLD FRONT IS ANALYZED OVER THE NE ATLC PORTION OF THE DISCUSSION AREA FROM 31N10W TO 30N20W TO 32N27W. ISOLATED SHOWERS ARE POSSIBLE WITHIN 90 NM EITHER SIDE OF THE FRONT. OTHERWISE...THE EASTERN ATLC IS UNDER THE INFLUENCE OF A 1019 MB HIGH CENTERED NEAR 28N30W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN