000 AXNT20 KNHC 212356 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SUN JUN 21 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... A TIGHT PRESSURE GRADIENT BETWEEN HIGH PRESSURE ACROSS THE WESTERN ATLC AND THE GULF OF MEXICO...AND A 1007 MB LOW OVER NORTHERN COLOMBIA IS SUPPORTING NEAR GALE FORCE WINDS OVER A PORTION OF THE SOUTH-CENTRAL CARIBBEAN TODAY. THE GRADIENT WILL TIGHTEN FURTHER TONIGHT...WHICH WILL RESULT IN GALE FORCE WINDS STARTING 10 TO 15 FT ARE EXPECTED. THESE GALE FORCE WINDS ARE FORECAST TO DIMINISH TOMORROW AHEAD OF A TROPICAL WAVE THAT WILL MOVE ACROSS THE CENTRAL CARIBBEAN TUE AND WED. PLEASE REFER TO THE HIGH SEAS FORECAST... MIAHSFAT2/FZNT02 KNHC...AND THE OFFSHORE FORECAST...MIAOFFNT3/ FZNT23 KNHC...FOR MORE DETAILS. ...TROPICAL WAVES... A TROPICAL WAVE IS APPROACHING THE CAPE VERDE ISLANDS OVER THE EASTERN ATLC WITH AXIS ALONG ROUGHLY 21N FROM 07N TO 16N...MOVING W AT AROUND 15 TO 20 KT. SSMI TPW IMAGERY INDICATES THIS WAVE REMAINS EMBEDDED IN A MODERATE MOIST ENVIRONMENT S OF 15N WITH METEOSAT IMAGERY INDICATING SAHARAN DUST AND DRY AIR N OF 15N. A TROPICAL WAVE IS OVER THE CENTRAL TROPICAL ATLC WITH AXIS ALONG 42W/43W FROM 05N TO 13N...MOVING W AT 20 KT OVER THE PAST 24 HOURS. AN ASCAT SATELLITE PASS FROM AROUND 1830 UTC INDICATED TRADE WINDS AROUND 20 KT FROM 12N TO 15N BETWEEN 45W AND 50W BETWEEN THE WAVE AND RIDGING NW OF THE WAVE. SSMI TPW IMAGERY SHOWS THE WAVE IS EMBEDDED IN A MODERATE MOIST ENVIRONMENT S OF 12N...EXCEPT IN THE NORTHERN REGION WHERE METEOSAT SATELLITE IMAGERY INDICATES SAHARAN DRY AIR AND DUST. NO DEEP CONVECTION IS NOTED WITH THE WAVE AT THIS TIME. A TROPICAL WAVE IS IN THE WESTERN TROPICAL ATLC APPROACHING THE WINDWARD ISLANDS. THIS WAVE HAS BEEN ACCOMPANIED BY A RELATIVELY HIGH AMOUNT OF LOWER LEVEL MOISTURE AND IS CURRENTLY INTERACTING WITH AN UPPER LOW CENTERED NORTH OF THE VIRGIN ISLANDS TO PRODUCE WIDESPREAD SHOWERS AND THUNDERSTORMS MAINLY SOUTH OF 15N THROUGHOUT THE WINDWARD ISLANDS. A REGIONAL RADAR MOSAIC IS SHOWING THE MAIN AREA OF CONVECTION OVER BARBADOS...WHERE AN OBSERVATION AT 19 UTC INDICATED GUSTS TO 34 KT. THE STRONG DOWNDRAFTS MAY BE DUE IN PART TO A DRIER PATTERN IN THE MID LEVELS OF THE ATMOSPHERE RELATED TO THE SAHARAN AIR LAYER. THE WAVE WILL PASS THE WINDWARD ISLANDS THROUGH OVERNIGHT...BRINGING CONTINUED SHOWERS AND THUNDERSTORMS WITH OCCASIONALLY HEAVY RAINFALL AND GUSTY WINDS TO THE ISLANDS THROUGH MONDAY. A FEW SHOWERS AND THUNDERSTORMS WILL ALSO IMPACT THE LEEWARD ISLANDS AS THE TROPICAL WAVE AND UPPER LOW SHIFT W OF THE AREA. A TROPICAL WAVE IS IN THE FAR SW CARIBBEAN BASIN IS STARTING TO SLOWLY MAKE LANDFALL INTO THE COASTS OF NICARAGUA AND COSTA RICA. SSMI TPW IMAGERY INDICATES THAT THERE IS ABUNDANT MOISTURE S OF 12N ALONG THE WAVE...WITH DRY AIR N OF 12N. A FEW SHOWERS AND THUNDERSTORMS ARE NOTED ALONG THE COAST FROM WESTERN PANAMA TO CENTRAL COSTA RICA DUE TO TRADE WIND CONVERGENCE AND SEA BREEZE EFFECTS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS AFRICA TO OVER SENEGAL NEAR 14N17W...RESUMING W OF A TROPICAL WAVE NEAR 08N23W AND CONTINUING TO 05N35W. THE ITCZ BEGINS NEAR 05N35W AND CONTINUES TO E OF A TROPICAL WAVE NEAR 06N42W. BESIDES THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...ONLY A FEW MODEST SHOWERS ARE NOTED WITHIN 120 NM N OF THE MONSOON TROUGH AXIS BETWEEN 25W AND 30W. ...DISCUSSION... THE GULF OF MEXICO... AN UPPER LOW REMAINS ANCHORED OVER THE YUCATAN PENINSULA. SUBSIDENCE ON THE WESTERN SIDE OF THIS FEATURE IS KEEPING THE WESTERN GULF MOSTLY CLOUD FREE. A FEW SHOWERS AND THUNDERSTORMS ARE NOTED OVER THE SE GULF UNDER DIVERGENCE ALOFT ASSOCIATED WITH THE UPPER LOW. A 1020 MB SURFACE HIGH REMAINS CENTERED OVER THE NORTHEAST GULF NEAR 27N87W. THIS IS MAINTAINING GENERALLY LIGHT TO GENTLE BREEZES OVER THE EASTERN GULF. RECENT OBSERVATIONS ALONG THE COAST OF TEXAS ALONG WITH A 16 UTC ASCAT SATELLITE PASS INDICATED MODERATE TO LOCALLY FRESH RETURN FLOW HAS SET UP OVER THE NW GULF BETWEEN THE HIGH PRES AND LOW PRES OVER N CENTRAL MEXICO. FARTHER SOUTH...A TROUGH HAS FORMED OVER THE YUCATAN PENINSULA DUE TO STRONG ADIABATIC WARMING. THE TROUGH WILL MIGRATE WEST TONIGHT IN PHASE WITH THE NORTHERN EXTENT OF A TROPICAL WAVE MOVING ACROSS CENTRAL AMERICA TO MAINTAIN MODERATE TO FRESH WINDS OVER THE SW GULF TONIGHT. SEAS ARE RANGING FROM 1 TO 3 FT OVER THE NE GULF...2 TO 4 FT OVER THE NW AND SE GULF...3 TO 5 FT IN THE SW GULF WITH LITTLE CHANGE EXPECTED THROUGH EARLY NEXT WEEK. THE CARIBBEAN SEA... STRONG RIDGING EXTENDS FROM THE WESTERN ATLC TO THE CENTRAL CARIBBEAN IN THE WAKE OF A TROPICAL WAVE MOVING INTO CENTRAL AMERICA. A TIGHT GRADIENT BETWEEN THE RIDGE AND LOW PRES OVER COLOMBIA IS RESULTING IN NEAR GALE FORCE WINDS ACROSS MUCH OF THE CENTRAL CARIBBEAN...PULSING TO GALE FORCE TONIGHT. ANOTHER TROPICAL WAVE APPROACHING THE WINDWARD ISLANDS WILL MOVE INTO THE EASTERN CARIBBEAN BY EARLY MON...AND INTO THE CENTRAL CARIBBEAN BY LATE TUE. THIS TROPICAL WAVE IS INTERACTING WITH A BROAD UPPER LOW CURRENTLY CENTERED JUST NORTH OF THE VIRGIN ISLANDS...AND WILL BRING INCREASED SHOWERS AND THUNDERSTORMS TO MUCH OF THE EASTERN AND CENTRAL CARIBBEAN THROUGH EARLY NEXT WEEK. ...HISPANIOLA... A FEW THUNDERSTORMS FORMED THIS AFTERNOON OVER THE NORTHERN AND CENTRAL MOUNTAIN RANGES OF THE DOMINICAN REPUBLIC BUT WERE SHEARED BY STRONG NORTHERLY FLOW ON THE WEST SIDE OF AN UPPER LOW CURRENTLY CENTERED NORTH OF THE VIRGIN ISLANDS. THE UPPER LOW ALONG WITH A TRAILING TROPICAL WAVE WILL MOVE WEST AND APPROACH EASTERN HISPANIOLA BY EARLY TUE. THE TROPICAL WAVE WILL MOVE SLOWLY THROUGH THE CENTRAL CARIBBEAN THROUGH MID WEEK...AND THE UPPER LOW WILL GENERALLY STALL OVER HISPANIOLA. THIS WILL INCREASE CHANCES FOR SHOWERS AND THUNDERSTORMS MAINLY DURING AFTERNOON HOURS OVER THE ISLAND EARLY TO MID WEEK. THE ATLANTIC OCEAN... S OF 31N W OF 60W...A FEW SHOWERS AND THUNDERSTORMS ARE NOTED ACROSS THE NORTHERN BAHAMAS AND WITHIN 300 NM NE OF THE NORTHERN BAHAMAS...RELATED TO DIVERGENCE ALOFT BETWEEN AN UPPER RIDGE CENTERED NEAR 29N72W AND AN UPPER LOW CENTERED JUST NORTH OF THE VIRGIN ISLANDS. THE SUBTROPICAL RIDGE AXIS EXTENDS EAST TO WEST ALONG ROUGHLY 29N...MAINTAINING LIGHT TO GENTLE BREEZES N OF 22N AND MODERATE TO FRESH WINDS SOUTH OF 22N. LOOKING AHEAD...THE NORTHERN PORTION OF A TROPICAL WAVE WILL TRAIL THE UPPER LOW AS IT SHIFT WESTWARD THROUGH MID WEEK...BRINGING AN SLIGHT INCREASE IN EAST WINDS PARTICULARLY N OF HISPANIOLA MON AND TUE ALONG WITH INCREASED SHOWERS AND THUNDERSTORMS S OF 22N. CENTRAL AND EASTERN ATLC...BROAD SURFACE RIDGING COVERS THE CENTRAL ATLC BEING ANCHORED BY A 1027 MB HIGH NEAR 28N41W...MAINTAINING GENTLE TO MODERATE BREEZES N OF 22N AND MODERATE TO FRESH TRADES S OF 22N...MAINLY NEAR TROPICAL WAVES. METEOSAT SATELLITE IMAGERY INDICATES SAHARAN DRY AIR AND DUST COVERING MOST OF THE TROPICS S OF 20N...MAINLY E OF 30W WHERE A NEW PLUME IS EMERGING OFF THE COAST OF NW AFRICA. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ CHRISTENSEN