684 FXUS62 KCHS 092020 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 420 PM EDT TUE JUL 9 2013 .SYNOPSIS... ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH THURSDAY. A WEAKENING COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST LATE THIS WEEK...THEN STALL OVER OR CLOSE TO THE AREA NEXT WEEKEND WHILE TROPICAL CYCLONE CHANTAL OR ITS REMNANTS APPROACH THE SOUTHEAST COAST. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... ATLANTIC HIGH PRESSURE WILL PREVAIL AT THE SFC WHILE MID LVL RIDGING GRADUALLY WEAKENS AND RETREATS OVER THE WESTERN ATLANTIC THIS EVENING. AS THIS OCCURS...SCATTERED SHOWERS AND/OR THUNDERSTORMS ARE EXPECTED TO CONTINUE UNTIL SUNSET WITH THE GREATEST COVERAGE OVER INLAND SOUTHEAST GEORGIA WHERE SBCAPES REMAIN BETWEEN 3000-4000 J/KG. EXPECT ENHANCED SHOWER/THUNDERSTORM ACTIVITY TO OCCUR MAINLY ALONG THE INLAND MOVING SEABREEZE THIS EVENING. SFC DEWPTS IN THE LOW 70S...PWATS NEAR 2.0 INCHES AND WEAK WIND FIELDS RESULTING IN SLOW STORM MOTIONS FAVOR SHOWERS AND/OR THUNDERSTORMS CAPABLE OF PRODUCING HEAVY RAINFALL AT TIMES. ALTHOUGH THE SEVERE WEATHER THREAT WILL REMAIN LOW...WE CAN NOT RULE OUT THE POSSIBILITY OF A STRONGER STORM OR TWO WITH BOUNDARY INTERACTIONS BEFORE SUNSET. WITH LITTLE SHEAR IN PLACE...SHOWERS AND THUNDERSTORMS WILL GRADUALLY DIMINISH LATE EVENING INTO THE EARLY OVERNIGHT HOURS WITH DIURNAL HEAT LOSS. IN GENERAL...CLOUD COVER WILL GRADUALLY DISSIPATE OVERNIGHT WITH SHOWERS/THUNDERSTORMS DIMINISHING...AND THERE REMAINS A POSSIBILITY OF PATCHY FOG INLAND FOR LOCATIONS THAT HAVE EXPERIENCED HEAVY RAINFALL TODAY...ESPECIALLY IN SOUTHEAST GEORGIA. HOWEVER...LATEST SOUNDINGS SUGGEST MID/HIGH CLOUDS MAY LIMIT STRONG RADIATIONAL COOLING NECESSARY FOR ANY FOG...THUS HAVE KEPT A FOG FREE FORECAST FOR ALL LOCATIONS OVERNIGHT. LOWS TEMPS WILL RANGE FROM THE LOW 70S INLAND...TO MID/UPPER 70S ALONG THE COAST. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... HIGH PRESSURE OVER THE AREA WILL BE BREAKING DOWN THROUGH THE PERIOD AS AN UPPER TROUGH AND ASSOCIATED SURFACE COLD FRONT MOVE INTO THE EASTERN CONUS. DEEP MOISTURE WILL BE SHIFTING EASTWARD OVER THE AREA WITH TIME AND THUS RAIN CHANCES WILL BE ON THE INCREASE TOWARD FRIDAY WITH THE POTENTIAL OF LOCALLY HEAVY RAINFALL GIVEN THE WEAK STORM MOTIONS AND UNSEASONABLY HIGH PRECIPITABLE WATERS LEVELS...MAINLY INLAND WEDNESDAY AND THEN EVERYWHERE THURSDAY AND FRIDAY. TEMPERATURES WILL GENERALLY BE NEAR NORMAL THROUGH THE PERIOD...HIGHS AROUND 90 AND LOWS IN THE LOWER TO MID 70S. HOWEVER...COOLER HIGHS ARE POSSIBLE DEPENDING ON RAIN/CLOUD COVERAGE...ESPECIALLY THURSDAY/FRIDAY. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... MAIN FORECAST CHALLENGE THIS PERIOD IS WHAT HAPPENS TO TROPICAL STORM CHANTAL. THE 12Z/09 GFS...ECMWF AND CANADIAN MODELS ARE IN FAIRLY GOOD AGREEMENT TAKING THE SYSTEM FROM AROUND THE BAHAMAS FRIDAY NIGHT TOWARD THE SC/GA COASTS SATURDAY...ALTHOUGH THEY ALL DIFFER WITH RESPECT TO THE STRENGTH OF THE SYSTEM. THE CANADIAN HAS PERSISTENTLY BEEN SHOWING A STRONGER SYSTEM MAKING LANDFALL ALONG THE SC/GA COASTS SO IT MAY BE ON TO SOMETHING. HOWEVER...THERE IS STILL QUITE A BIT OF UNCERTAINTY REGARDING HOW STRONG THE STORM WILL BE AFTER HITTING HISPANIOLA AND THUS HOW DEEP OF ATMOSPHERIC FLOW IT WILL BE STEERED BY. THE MORE NORTHERN TRACK TREND IS CERTAINLY DISCONCERTING SO WE URGE EVERYONE ACROSS THE AREA TO PAY CLOSE ATTENTION TO THIS SYSTEM THROUGH THE WEEKEND. WHETHER CHANTAL REMAINS A NAMED STORM OR NOT THERE WILL STILL BE QUITE A BIT OF RAINFALL ACROSS THE AREA THROUGH THE WEEKEND AND POSSIBLY INTO EARLY NEXT WEEK GIVEN THE DEEP TROPICAL MOISTURE MOVING IN AHEAD OF AN APPROACHING/WEAKENING COLD FRONT WHICH WILL STALL OUT OVER THE AREA. SEVERAL INCHES OF RAINFALL COULD OCCUR THROUGH THE PERIOD...WITH EVEN MORE RAINFALL POSSIBLE IN ISOLATED SPOTS AND ESPECIALLY IF CHANTAL MOVES DIRECTLY TOWARD THE AREA. TEMPERATURES GENERALLY CLOSE TO NORMAL ALTHOUGH HIGH COULD EASILY BE BELOW NORMAL DEPENDING ON THE TRACK OF CHANTAL. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... VFR CIGS/VSBYS ARE EXPECTED THROUGH 18Z WEDNESDAY. ISOLATED TO SCATTERED SHRA/TSRA WILL DEVELOP NEAR THE TERMINALS THIS AFTERNOON BEFORE DRIFTING INLAND WITH A SEABREEZE BY LATE AFTERNOON. EXTENDED AVIATION OUTLOOK...LOW PROBABILITIES OF FOG/STRATUS AROUND SUNRISE EACH MORNING. LOW CHANCES FOR DIRECT IMPACTS FROM MAINLY AFTERNOON/EVENING SHOWERS/THUNDERSTORMS...ALTHOUGH THE TRACK OF CHANTAL WILL LARGELY DETERMINE THE WIND/RAIN IMPACTS THIS WEEKEND. && .MARINE... TONIGHT...QUIET CONDITIONS WILL REMAIN OVER THE COASTAL WATERS ALONG THE WESTERN PERIPHERY OF A PERSISTENT SUB-TROPICAL ATLANTIC RIDGE. THIS WILL RESULT IN WINDS/SEAS WELL BELOW SMALL CRAFT ADVISORY THRESHOLDS. IN GENERAL...SOUTHERLY WINDS WILL REMAIN AT OR BELOW 10 KTS OVER ALL WATERS WITH MINOR FLUCTUATIONS IN SPEEDS AND DIRECTIONS ALONG THE COAST. WIND DRIVEN WAVES AND SMALL SWELLS WILL RESULT IN SIGNIFICANT WAVE HEIGHTS NO HIGHER THAN 2-3 FT. WEDNESDAY THROUGH SUNDAY...ATLANTIC HIGH PRESSURE WILL BREAK DOWN INTO LATE WEEK AS A COLD FRONT APPROACHES FROM THE NORTHWEST AND EVENTUALLY STALLS OVER THE AREA THIS WEEKEND. MEANWHILE TROPICAL STORM CHANTAL IS FORECAST TO BE NEAR THE BAHAMAS...POSSIBLY APPROACHING THE GA/SC COASTAL WATERS THIS WEEKEND. DUE TO THE UNCERTAINTY WITH REGARD TO THIS SYSTEM WE HAVE CAPPED WINDS BELOW ADVISORY LEVELS /NEAR 20 KT/ ALTHOUGH DO INDICATE ADVISORY LEVEL SEAS. MARINERS ARE URGED TO PAY CLOSE ATTENTION TO THE LATEST FORECASTS. && .HYDROLOGY... AN APPROACHING COLD FRONT IS EXPECTED TO WEAKEN AND STALL OUT OVER THE AREA FRIDAY INTO SATURDAY. AHEAD OF THE FRONT DEEP TROPICAL MOISTURE WILL BE MOVING INTO THE AREA. SLOW STORM MOTIONS WILL MEAN THE POTENTIAL FOR HEAVY RAINFALL AND LOCALIZED FLOODING THURSDAY THROUGH THE WEEKEND...POSSIBLY LASTING INTO EARLY NEXT WEEK...ESPECIALLY IF TROPICAL CYCLONE CHANTAL DIRECTLY IMPACTS THE AREA. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...DPB SHORT TERM...RJB LONG TERM...RJB AVIATION...DPB/RJB MARINE...DPB/RJB HYDROLOGY...RJB