000 AXNT20 KNHC 061802 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SUN SEP 06 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 1745 UTC. ...SPECIAL FEATURES... THE CENTER OF TROPICAL DEPRESSION FRED AT 06/15 UTC IS NEAR 25.7N 43.2W. FRED IS MOVING TOWARD THE NORTH...OR 5 DEGREES AT 8 KT. THE MINIMUM CENTRAL PRESSURE IS 1010 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PUBLIC ADVISORIES ABOUT FRED ARE BEING ISSUED UNDER THE WMO HEADER WTNT31 KNHC...AND UNDER THE AWIPS HEADER MIATCPAT1. FORECAST/ADVISORIES BEING ISSUED UNDER THE WMO HEADER WTNT21 KNHC...AND UNDER THE AWIPS HEADER MIATCMAT1. CONVECTIVE PRECIPITATION...SCATTERED MODERATE TO ISOLATED STRONG WITH TSTMS FROM 22N TO 29N BETWEEN 39W AND 45W. THE CENTER OF TROPICAL STORM GRACE AT 06/1500 UTC IS NEAR 12.9N 29.9W. GRACE IS MOVING TOWARD THE WEST...OR 280 DEGREES AT 12 KT. THE MINIMUM CENTRAL PRESSURE IS 1004 MB. MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. PUBLIC ADVISORIES ABOUT GRACE ARE BEING ISSUED UNDER THE WMO HEADER WTNT32 KNHC...AND UNDER THE AWIPS HEADER MIATCPAT2. FORECAST/ADVISORIES ARE BEING ISSUED UNDER THE WMO HEADER WTNT22 KNHC...AND UNDER THE AWIPS HEADER MIATCMAT2. CONVECTIVE PRECIPITATION...SCATTERED MODERATE FROM 08N TO 16N BETWEEN 26W AND 32W. ...TROPICAL WAVES... A TROPICAL WAVE IS OVER THE CENTRAL ATLC...AHEAD OF TROPICAL STORM GRACE...WITH AXIS NEAR 38W MOVING W AT APPROXIMATELY 15 KT OVER THE PAST 24 HOURS. CIRA LAYER PRECIPITABLE WATER IMAGERY SHOW THERE IS DRY AIR IN THE WAVE ENVIRONMENT...COINCIDING WITH SAHARAN AIR DEPICTED IN METEOSAT ENHANCED IMAGERY. ISOLATED SHOWERS ARE FROM 12N TO 13N BETWEEN 37W AND 39W. A TROPICAL WAVE IS WITHIN 500 NM E OF THE LESSER ANTILLES. THIS IS A LOW-AMPLITUDE WAVE WITH A WELL DEFINED INVERTED-V WIND PATTERN AT 700 MB AND A WEAK CYCLONIC SWIRL NEAR THE SURFACE. CIRA LAYER PRECIPITABLE WATER IMAGERY SHOW MODERATE MOISTURE ASSOCIATED WITH THIS WAVE MAINLY WITHIN 320 NM AHEAD OF ITS AXIS S OF 14N WHERE SCATTERED SHOWERS ARE OBSERVED. A TROPICAL WAVE IS OVER THE E CARIBBEAN WITH AXIS NEAR 68W...MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. CIRA LAYER PRECIPITABLE WATER IMAGERY FROM SURFACE TO 850 MB SHOW A MODERATE AIRMASS AHEAD OF THE WAVE AXIS AND DRY AIR BEHIND IT. THE MOISTURE AND A SLIGHT DIFFLUENT MIDDLE-LEVEL ENVIRONMENT MAY ENHANCE SCATTERED SHOWERS AND TSTMS OVER PUERTO RICO AND ADJACENT WATERS LATER TODAY. A TROPICAL WAVE IS OVER THE CENTRAL CARIBBEAN WITH AXIS ALONG 74W...MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. THE WAVE IS ASSOCIATED MAINLY WITH MODERATE MOISTURE FROM THE SURFACE TO 850 MB ACCORDING TO CIRA LAYER PRECIPITABLE WATER IMAGERY. HOWEVER...STRONG DEEP LAYER WIND SHEAR AND DRY AIR SUBSIDENCE FROM ALOFT HINDER CONVECTION DEVELOPMENT AT THE TIME. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH PASSES OVER COASTAL SECTIONS OF AFRICA NEAR 12N16W TO 10N21W. THE ITCZ BEGINS NEAR 09N41W AND CONTINUES TO 09N49W TO 09N56W. ASIDE THE CONVECTION ASSOCIATED WITH GRACE...SCATTERED MODERATE CONVECTION IS OFF THE WESTERN COAST OF AFRICA FROM 06N TO 15N E OF 20W...ASSOCIATED WITH BOTH THE NEXT TROPICAL WAVE TO COME OFF THE COAST AND THE MONSOON TROUGH. ...DISCUSSION... GULF OF MEXICO... A BROAD SURFACE RIDGE COVERS THE EASTERN CONUS AND EXTENDS A RIDGE AXIS ACROSS THE N-NE GULF OF MEXICO. IN THE GULF...A WEAKNESS IN THIS RIDGE IS ANALYZED AS A 1017 MB LOW NEAR 27N85W. ALOFT...A BROAD ANTICYCLONE IS CENTERED OVER TEXAS EXTENDING INTO THE W-NW BASIN WHILE AN ELONGATED LOW WITH ASSOCIATED TROUGH COVER MOST OF THE EASTERN CONUS WITH A BASE EXTENDING TO THE BAY OF CAMPECHE AND THE YUCATAN PENINSULA. THIS WIND PATTERN ALOFT IS GENERATING A DIFFLUENT ENVIRONMENT THAT ALONG WITH SHALLOW MOISTURE BEING ADVECTED FROM THE CARIBBEAN SUPPORT SCATTERED MODERATE CONVECTION AND TSTMS N OF 25N E OF 93W AND ISOLATED SHOWERS AND TSTMS IN THE SE GULF. WINDS ACROSS THE GULF CONTINUE TO BE VARIABLE AND LIGHT. WEAK RIDGING WILL CONTINUE ACROSS THE BASIN THE NEXT TWO DAYS. CARIBBEAN SEA... TWO TROPICAL WAVES ARE OVER THE BASIN. NONE PRODUCING SIGNIFICANT WEATHER AT THE TIME. SEE THE TROPICAL WAVES SECTION FOR MORE DETAILS. THE EASTERN PORTION OF AN UPPER TROUGH EXTENDING ALONG THE EASTERN CONUS WITH BASE REACHING THE S-SW GULF OF MEXICO ALONG WITH AN UPPER RIDGE CENTERED OVER THE SW CARIBBEAN CONTINUE TO GENERATE A DIFFLUENT ENVIRONMENT OVER THE NW CARIBBEAN THAT ENHANCES ISOLATED SHOWERS AND TSTMS W OF 80W. OVER THE SW BASIN...THE MONSOON TROUGH CONTINUE TO SUPPORT SCATTERED MODERATE CONVECTION AND ISOLATED TSTMS S OF 13N W OF 75W. EXCEPT FOR SCATTERED TO ISOLATED SHOWERS OVER THE WINDWARD ISLANDS...THE REMAINDER BASIN IS DEVOID OF CONVECTION BEING INFLUENCED BY DRY AIR SUBSIDENCE AND STRONG DEEP LAYER WIND SHEAR. THE WAVES ARE EXPECTED TO BE OVER THE W BASIN BY TUESDAY MORNING. ...HISPANIOLA... SHALLOW MOISTURE AND A MIDDLE TO UPPER LEVEL DIFFLUENT ENVIRONMENT ALOFT SUPPORT ISOLATED SHOWERS AND TSTMS OVER THE NE DOMINICAN REPUBLIC. THE PASSAGE OF TWO TROPICAL WAVES OVER THE ISLAND IS EXPECTED TO GENERATE SOME SHOWERS THROUGH MONDAY. ATLANTIC OCEAN... THE MAIN FEATURES IN THE BASIN CONTINUE TO BE TROPICAL DEPRESSION FRED AND TROPICAL STORM GRACE...BOTH DISCUSSED IN THE SPECIAL FEATURES SECTION. TWO TROPICAL WAVES ARE AHEAD OF GRACE...NONE GENERATING SIGNIFICANT WEATHER AT THE TIME. PLEASE REFER TO THE TROPICAL WAVES SECTION FOR MORE DETAILS. WEAK LOW PRESSURE DOMINATES THE SW N ATLC WATERS BEING SUPPORTED BY A LOW ALOFT CENTERED OVER THE SE CONUS. ONE SURFACE TROUGH IS ANALYZED IN THIS REGION FROM 28N70W SW TO 25N75W AND ENHANCES ISOLATED SHOWERS AND TSTMS OVER THE NORTHERN BAHAMAS AND FROM 25N TO 28N BETWEEN 65W AND 72W. A MIDDLE TO UPPER LEVEL TROUGH IS OVER THE CENTRAL ATLC WITH BASE REACHING NEARLY 30N...SUPPORTING A FRONTAL SYSTEM ANALYZED AS A STATIONARY FRONT FROM 30N52W TO 30N60W TO 29N67W. SCATTERED MODERATE CONVECTION IS N OF 27N BETWEEN 45W AND 51W. WEAK RIDGING DOMINATES ELSEWHERE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ NR