000 AXNT20 KNHC 141730 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON SEP 14 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1700 UTC. ...SPECIAL FEATURE... A WEAK 1013 MB LOW PRES AREA IS CENTERED NEAR 11N39W AT THE BASE OF A TROPICAL WAVE EXTENDING NORTHWARD TO 17N38W. THE CIRCULATION IS WELL DEFINED BUT ELONGATED EAST TO WEST ALONG THE MONSOON TROUGH. CONVECTION IS MINIMAL CURRENTLY...WITH ONLY A FEW SHOWERS NOTED WITHIN 75 NM OF THE WESTERN QUADRANT OF THE CENTER. THIS IS DUE TO STRONG EASTERN SHEAR ALOFT ALONG THE SOUTHERN PERIPHERY OF AN UPPER ANTICYCLONE PARKED TO THE NORTH. THERE IS ALSO SOME DRY AIR ENTRAINMENT INHIBITING CONVECTIVE DEVELOPMENT. DESPITE THE CURRENT CHALLENGES IN PLACE FOR FURTHER DEVELOPMENT... ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR DEVELOPMENT...AND THIS SYSTEM IS LIKELY TO BECOME A TROPICAL DEPRESSION DURING THE NEXT DAY OR TWO WHILE IT MOVES GENERALLY NW ACROSS THE CENTRAL TROPICAL ATLC. ...TROPICAL WAVES... A TROPICAL WAVE IS OVER THE E TROPICAL ATLC WITH AXIS E OF THE CAPE VERDE ISLANDS ALONG 20W FROM 09N17N. CONVECTION IS INCREASING AROUND A DEVELOPING LOW PRES SYSTEM AT THE BASE OF THE TROPICAL WAVE NEAR 08N20W. EASTERLY FLOW TO THE NORTH OF THE LOW PRES IS DRAWING DRY AIR ACROSS THE NORTHERN PORTION OF THE TROPICAL WAVE. A TROPICAL WAVE IS ANALYZED NEAR 60W FROM 11N TO 20N MOVING THROUGH THE LEEWARD AND WINDWARD ISLANDS AND APPROACHING THE EASTERN CARIBBEAN. SOUNDING DATA FROM YESTERDAY AND THIS MORNING FROM ACROSS THE LEEWARD AND WINDWARD ISLANDS ARE DOCUMENTING A THE APPROACH AND PASSAGE TO THE LOWER TO MID LEVEL AXIS OF THE TROPICAL WAVE. MOST OF THE MOISTURE IS LAGGING TO THE EAST OF THIS AXIS WITH REGIONAL RADAR INDICATING AREAS OF SHOWERS MAINLY NORTH OF BARBADOS AND EAST OF THE LEEWARD ISLANDS. A TROPICAL WAVE IS ANALYZED IN THE WESTERN CARIBBEAN BETWEEN EASTERN PANAMA AND JAMAICA. A FEW DIMINISHING SHOWERS AND THUNDERSTORMS ARE NOTED ON THE NORTHERN END OF THE WAVE AXIS...BETWEEN JAMAICA AND EASTERN CUBA...ALTHOUGH THIS IS RELATED TO AN UPPER TROUGH LOCATED NE OF THE AREA. OTHERWISE NO SIGNIFICANT CONVECTION IS NOTED. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM 11N15W TO A 1012 MB LOW NEAR 08N17W TO 13N30W TO 1013 MB LOW PRES NEAR 11N38W. FOR CONVECTION INFORMATION SEE THE TROPICAL WAVES AND SPECIAL FEATURES SECTIONS. OTHERWISE...A CLUSTER OF MODERATE CONVECTION IS FROM 11N TO 12N BETWEEN 50W AND 52W. ...DISCUSSION... GULF OF MEXICO... A STATIONARY FRONT REACHES FROM W CENTRAL FLORIDA TO NEAR THE MOUTH OF THE RIO GRANDE RIVER. A WEAK LOW PRES AREA OFF THE COAST OF TAMPICO MEXICO APPEARS TO BE DISSIPATING INTO A TROUGH JUDGING FROM LATEST OBSERVATIONS FROM AROUND THE AREA...ALTHOUGH SHARP CYCLONIC TURNING IS STILL OVER THE FAR WESTERN GULF. SHOWERS AND THUNDERSTORMS PERSIST OVER THE SW GULF...ENHANCED IN PART BY UPPER DYNAMICS AHEAD OF AN AMPLIFYING UPPER TROUGH MOVING FROM THE SOUTHERN PLAINS INTO THE MISSISSIPPI VALLEY. A FEW SHOWERS AND THUNDERSTORMS ARE NOTED ACROSS THE NORTHERN GULF AS WELL...THE RESULT OF OVERRUNNING OF MOIST UNSTABLE AIR ACROSS THE STATIONARY BOUNDARY. THE FRONT IS EXPECTED TO START DISSIPATING TONIGHT WHILE SURFACE RIDGING BUILDS AND PERSISTS THROUGH MID WEEK. CARIBBEAN SEA... A SURFACE RIDGE EXTENDS ACROSS MUCH OF THE EASTERN AND CENTRAL CARIBBEAN...BETWEEN THE TROPICAL WAVE MOVING ACROSS THE LEEWARD AND WINDWARD ISLANDS...AND THE OTHER TROPICAL WAVE MOVING ACROSS THE WESTERN CARIBBEAN. THE RESULTANT TIGHT GRADIENT IS MAINTAINING FRESH TO OCCASIONALLY STRONG TRADE WINDS OVER PRIMARILY THE S CENTRAL CARIBBEAN. GENERALLY LIGHT TO MODERATE FLOW PREVAILS OVER THE NW CARIBBEAN. A FEW SHOWERS ARE NOTED OVER THE EASTERN CARIBBEAN ASSOCIATED WITH THE APPROACHING TROPICAL WAVE. SCATTERED SHOWERS AND THUNDERSTORMS ARE NOTED BETWEEN JAMAICA AND EASTERN CUBA...ASSOCIATED WITH CONVERGENT OFFSHORE FLOW FROM OVERNIGHT ENHANCED BY UPPER DIVERGENCE ASSOCIATED WITH UPPER TROUGHING TO THE NORTHEAST. THIS ACTIVITY IS DECREASING RAPIDLY AS THE OFFSHORE FLOW DIMINISHES RAPIDLY. ELSEWHERE GENERALLY FAIR WEATHER PREVAILS. ...HISPANIOLA... AN UPPER LEVEL TROUGH EXTENDS FROM AN UPPER LOW CENTERED OVER THE SOUTHERN BAHAMAS TO ANOTHER BROADER UPPER LOW OVER THE CENTRAL CARIBBEAN. THE UPPER LOW OVER THE SOUTHERN BAHAMAS HAD DRIFTED FROM A POSITION OVER HISPANIOLA YESTERDAY...DRAWING MOST OF THE MAIN DEEP LAYER MOISTURE WITH IT. THIS HAS ALLOWED SLIGHTLY LESS OFFSHORE SHOWER AND THUNDERSTORM ACTIVITY OVERNIGHT. AFTERNOON CONVECTION APPEARS TO BE STARTING OVER THE SE PORTION OF THE DOMINICAN REPUBLIC CURRENTLY...BUT OVERALL COVERAGE ACROSS THE ISLAND MAY BE SLIGHTLY LESS THAN YESTERDAY INTO TUESDAY. MOISTURE AND INSTABILITY ASSOCIATED THE APPROACHING TROPICAL WAVE WILL INCREASE CHANCES FOR SHOWERS AND THUNDERSTORMS BY MID WEEK. ATLANTIC OCEAN... A COLD FRONT REACHES FROM NEAR 32N72W TO EAST CENTRAL FLORIDA...SUPPORTED BY AN ACTIVE UPPER TROUGH MOVING OFF THE EAST COAST OF THE UNITED STATES. SCATTERED SHOWERS AND THUNDERSTORMS ARE NOTED WITHIN 180 NM E OF THE BOUNDARY. THE FRONT WILL MOVE TO THE EAST AND SOUTH REACHING FROM 31N60W TO 27N65W THEN STALLING AND DISSIPATING ACROSS THE NORTHERN BAHAMAS THROUGH MID WEEK. FARTHER EAST...AN UPPER LOW IS CENTERED NEAR 25N62W. AN ASSOCIATED SURFACE TROUGH REACHES FROM 27N55W TO 23N60W. SCATTERED SHOWERS AND A FEW THUNDERSTORMS ARE NOTED WITHIN 180 NM NW OF THE TROUGH AXIS. THE TROUGH WILL SHIFT EASTWARD TO 45W THROUGH MID WEEK. RIDGING PERSIST FROM 20N TO 32N E OF 60W...WITH THE EXCEPTION OF A WEAK SURFACE JUST WEST OF THE CANARY ISLANDS. DRY SAHARAN AIR LAYER CONDITIONS CONTINUE TO INHIBIT CONVECTION N OF 20N. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ CHRISTENSEN