000 AXNT20 KNHC 060004 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SAT SEP 05 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 2345 UTC. ...SPECIAL FEATURES... FORMER TROPICAL STORM FRED HAS WEAKENED TO A DEPRESSION AT 05/2100 UTC. ITS CENTER IS LOCATED NEAR 23.8N 42.5W WITH A MINIMUM PRESSURE OF 1008 MB. FRED IS MOVING NORTHWEST...OR 315 DEGREES...AT 5 KNOTS. MAXIMUM SUSTAINED WINDS ARE 30 KNOTS WITH GUSTS TO 40 KNOTS. ISOLATED SHOWERS AND TSTMS ARE FROM 21N TO 26N BETWEEN 39W AND 45W. PUBLIC ADVISORIES ABOUT FRED ARE BEING ISSUED UNDER THE AWIPS/WMO HEADER TCPAT1/WTNT31 KNHC... FORECAST/ADVISORIES ISSUED UNDER THE AWIPS/WMO HEADER TCMAT1/WTNT21 KNHC. TROPICAL DEPRESSION SEVEN INTENSIFIED TO TROPICAL STORM GRACE AT 05/2100 UTC. THE CENTER OF THE STORM IS NEAR 12.6N 26.4W OR 248 NM SW OF THE CAPE VERDE ISLANDS. THE MINIMUM CENTRAL PRESSURE IS 1007 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. SCATTERED MODERATE CONVECTION IS FROM 10N TO 13N BETWEEN 25W AND 28W. PUBLIC ADVISORIES ABOUT GRACE ARE BEING ISSUED UNDER THE AWIPS/WMO HEADER TCPAT2/WTNT32 KNHC AND FORECAST/ADVISORIES UNDER THE AWIPS/WMO HEADER TCMAT2/WTNT22 KNHC. ...TROPICAL WAVES... A TROPICAL WAVE IS OVER THE CENTRAL ATLC ASSOCIATED WITH A 1012 MB LOW NEAR 11N33W AND IT HAS BEEN MOVING W AT 15 KT OVER THE PAST 24 HOURS. CIRA LAYER PRECIPITABLE WATER IMAGERY SHOW THERE IS DRY AIR INTRUSION INTO THE W-NW WAVE ENVIRONMENT ASSOCIATED WITH THE SAHARAN AIR LAYER. ISOLATED SHOWERS ARE FROM 08N TO 13N BETWEEN 32W AND 39W. A TROPICAL WAVE IS OVER THE E CARIBBEAN WITH AXIS NEAR 63W...MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. CIRA LAYER PRECIPITABLE WATER IMAGERY FROM SURFACE TO 850 MB SHOW THE WAVE IS MAINLY EMBEDDED IN A DRY ENVIRONMENT THAT ALONG WITH STRONG DEEP LAYER WIND SHEAR IN THE NE BASIN SUPPRESS CONVECTION DEVELOPMENT. SHALLOW MOISTURE IS NW AND SE OF THE ITS AXIS...ENHANCING ISOLATED SHOWERS OVER PUERTO RICO AND ADJACENT WATERS AND THE WINDWARD ISLANDS. A TROPICAL WAVE IS OVER THE CENTRAL CARIBBEAN WITH AXIS ALONG 70W...MOVING W AT 10 TO 15 KT OVER THE PAST 24 HOURS. MODERATE MOISTURE FROM THE SURFACE TO NEARLY 850 MB IS MAINLY NE OF THE WAVE AXIS WHILE DRY AIR COVERS THE REMAINDER WAVE ENVIRONMENT. STRONG DEEP LAYER WIND SHEAR ALONG WITH THE DRY AIR HINDER CONVECTION AT THE TIME. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH PASSES OVER COASTAL SECTIONS OF AFRICA NEAR 16N16W TO 14N20W. IT THEN RESUMES WEST OF TROPICAL STORM GRACE NEAR 12N29W TO A 1012 MB LOW NEAR 11N33W TO 10N36W. THE ITCZ BEGINS NEAR 10N37W AND CONTINUES TO 10N53W. FOR CONVECTION INFORMATION SEE SPECIAL FEATURES AND TROPICAL WAVES SECTION. ...DISCUSSION... GULF OF MEXICO... A BROAD SURFACE RIDGE COVERS THE EASTERN CONUS AND PORTIONS OF THE CENTRAL U.S. AND EXTENDS A RIDGE AXIS ACROSS THE NORTHERN AND CENTRAL GULF OF MEXICO. IN THE GULF...THE RIDGE IS BEING ANCHORED BY A 1016 MB HIGH LOCATED NEAR 26N90W...WHICH PROVIDES VARIABLE LIGHT WINDS OF 5 KT ACROSS THE BASIN. A WEAKNESS IN THIS RIDGE IS ANALYZED AS A 1015 MB LOW OVER SOUTHERN MISSISSIPPI WITH SURFACE TROUGH EXTENDING ACROSS THE FLORIDA PANHANDLE. ALOFT...A BROAD ANTICYCLONE CENTERED OVER TEXAS AND A TROUGH OVER THE EASTERN CONUS GENERATE A DIFFLUENT ENVIRONMENT ALOFT THAT ALONG WITH SHALLOW MOISTURE ADVECTED FROM THE CARIBBEAN SUPPORT SCATTERED MODERATE CONVECTION N OF 23N E OF 92W. HIGH PRESSURE IS EXPECTED ACROSS THE BASIN THE NEXT TWO DAYS. CARIBBEAN SEA... TWO TROPICAL WAVES ARE OVER THE BASIN. NONE PRODUCING SIGNIFICANT WEATHER. SEE THE TROPICAL WAVES SECTION FOR MORE DETAILS. THE BASE OF AN UPPER TROUGH OVER THE EASTERN CONUS EXTENDS TO THE NW CARIBBEAN GENERATING A DIFFLUENT ENVIRONMENT ALOFT THAT ALONG WITH SHALLOW MOISTURE IN THIS REGION SUPPORT SCATTERED TO ISOLATED SHOWERS AND TSTMS ALONG CUBA AND N OF 14N W OF 80W. OVER THE SW BASIN...A LOW PRESSURE CENTER OVER NORTHERN COLOMBIA ALONG WITH THE MONSOON TROUGH SUPPORT HEAVY SHOWERS AND TSTMS S OF 12N W OF 77W. THE REMAINDER BASIN IS DEVOID OF CONVECTION 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-LEVEL DIFFLUENT ENVIRONMENT SUPPORT SCATTERED SHOWERS AND TSTMS OVER THE SW DOMINICAN REPUBLIC AND HAITI. THE PASSAGE OF TWO TROPICAL WAVES ARE EXPECTED TO GENERATE SOME SHOWERS THROUGH MONDAY. ATLANTIC OCEAN... THE MAIN FEATURES IN THE BASIN ARE FRED THAT WEAKENED TO A DEPRESSION AND TROPICAL STORM GRACE...BOTH DISCUSSED IN THE SPECIAL FEATURES SECTION. A TROPICAL WAVES IS AHEAD OF GRACE WITH AN ASSOCIATED 1012 MB LOW PRESSURE CENTER. PLEASE REFER TO THE TROPICAL WAVES SECTION FOR MORE DETAILS. LOW PRESSURE DOMINATES THE SW N ATLC WATERS BEING SUPPORTED BY A BROAD TROUGH ALOFT. ONE SURFACE TROUGH IS ANALYZED FROM 29N65W SW TO 27N71W TO 26N77W AND ENHANCES SCATTERED SHOWERS AND TSTMS OVER THE EASTERN FLORIDA SEABOARD AND NORTHERN BAHAMAS AND FROM 25N TO 30N BETWEEN 65W AND 70W. ANOTHER TROUGH IS ANALYZED FROM 30N57W TO 26N64W. SIMILAR CONVECTION IS N OF 26N BETWEEN 48W AND 61W. RIDGING IS EXPECTED TO BUILD OVER THE SW N ATLC BY SUNDAY MORNING AND CONTINUE THROUGH MONDAY. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ NR