Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 281424 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 1024 AM EDT FRI AUG 28 2015 .SYNOPSIS... A STATIONARY FRONT WILL DISSIPATE NEAR THE COAST TODAY. ATLANTIC HIGH PRESSURE WILL REMAIN IN PLACE INTO EARLY NEXT WEEK. TROPICAL CYCLONE ERIKA COULD IMPACT THE SOUTHEAST UNITED STATES BY THE MIDDLE OF NEXT WEEK. REFER TO THE LATEST ADVISORY ON ERIKA ISSUED BY THE NATIONAL HURRICANE CENTER. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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MID-MORNING UPDATE... LOW LEVEL STRATUS DECK CONTINUES TO HANG ON ACROSS MUCH OF SOUTHEAST GA WELL PAST SUNRISE. UPDATED SKY COVER AND MORNING TEMPS TO REFLECT THIS PATTERN. STILL ANTICIPATE THAT WE WILL BREAK OUT ACROSS THE AREA WITHIN THE NEXT COUPLE OF HOURS AND TEMPS SHOULD REBOUND QUICKLY AFTER THAT...SO LITTLE CHANCE IN FORECAST HIGH TEMPS. OTHERWISE...POP FORECAST IS ON TRACK AND MORNING SHOWERS HAVE REMAINED FOCUSED ALONG THE STATIONARY FRONT SO FAR THIS MORNING. PREVIOUS DISCUSSION...A DECAYING STATIONARY FRONT WILL EXTEND FROM THE SOUTH CAROLINA COASTAL WATERS INTO THE I-95 CORRIDOR OF SOUTHEAST GEORGIA TODAY AS HIGH PRESSURE TRIES TO NUDGE IN FROM THE NORTH. MODELS ARE SIMILAR IN SHOWING THE BETTER CHANCES FOR SHOWERS/TSTMS FOCUSING ROUGHLY ALONG/EAST OF A GLENNVILLE- SAVANNAH-HILTON HEAD LINE TODAY WHERE THE SOUTHWEST-NORTHEAST ORIENTED RESULTANT SEA BREEZE WILL INTERSECT THE DECAYING STATIONARY FRONT. THIS ENHANCEMENT TO THE LOW-LEVEL CONVERGENCE FIELD COMBINED WITH MODEST INSTABILITY AND WEAK UVM INDUCED BY PASSING IMPULSES OF MID-LEVEL VORTICITY EJECTING NORTHEAST AHEAD AHEAD OF A PRONOUNCED NORTH-SOUTH SHEAR AXIS OVER THE NORTHERN GULF/SOUTHERN MISSISSIPPI VALLEY WILL SUPPORT ISOLATED TO SCATTERED SHOWERS/TSTMS. 20-40 PERCENT POPS LOOK REASONABLE TODAY GIVEN THE SYNOPTIC SETUP. IT IS VERY POSSIBLE COMMUNITIES FROM ALLENDALE TO THE CHARLESTON METRO AREA AND POINTS NORTH WILL SEE LITTLE TO NO CONVECTION AS THE ATMOSPHERE LOOKS TO BECOME INCREASING CAPPED IN RESPONSE TO LOWERING 700 HPA THETA-E ASSOCIATED WITH THE SOUTHERN FRINGE OF A SHORTWAVE RIDGE POSITIONED OVER CENTRAL/EASTERN NORTH CAROLINA AND THE VIRGINIA TIDEWATER. HIGHS WILL RANGE FROM UPPER 80S TO AROUND 90 INLAND TO THE MID 80S AT THE BEACHES.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... TONIGHT...CONVECTION WILL DISSIPATE QUICKLY THIS EVENING. ISOLATED TO PERHAPS SCATTERED SHOWERS/TSTMS COULD RE-FIRE OVER THE ATLANTIC AS LOW-LEVEL CONVERGENCE INCREASES ALONG THE WESTERN WALL OF THE GULF STREAM. WITH AND EAST/NORTHEAST LOW-LEVEL FLOW IN PLACE...SOME OF THIS ACTIVITY COULD MAKE A RUN FOR THE BEACHES...ESPECIALLY FROM HILTON HEAD SOUTH TO DARIEN AND SAPELO ISLAND GIVEN THE ORIENTATION OF THE COASTLINE. 20-30 PERCENT POPS WILL BE MAINTAINED OVERNIGHT AT THE COAST TO ACCOUNT FOR THIS WITH DRY CONDITIONS INLAND. LOWS WILL RANGE FROM THE LOWER 70S INLAND WITH MID-UPPER 70S AT THE BEACHES. SATURDAY INTO SATURDAY NIGHT...28/00Z GUIDANCE SUGGESTS THAT DRIER AIR WILL PUSH INTO NORTHERN COUNTIES OF THE FORECAST AREA...WHILE THE UPPER LOW CENTERED WEST OF THE REGION WILL CONTINUE TO PUSH MOISTURE INTO SOUTHERN COUNTIES OF THE FORECAST AREA. THIS SCENARIO COULD SUPPORT A FAIRLY SIGNIFICANT NORTH TO SOUTH MOISTURE GRADIENT. ACCORDINGLY...MAXIMUM POPS ARE GRADUATED FROM SLIGHT CHANCE NORTH TO HIGH CHANCE SOUTH...AND LOCALLY HIGHER POPS COULD EVENTUALLY BE REQUIRED ACROSS THE SOUTH. PWATS AROUND 2 INCHES AND WEAK STEERING FLOW COULD SUPPORT LOCALLY HEAVY RAIN ACROSS THE SOUTHERN 1/2 OF THE FORECAST AREA. SUNDAY INTO MONDAY...THE UPPER LOW SHOULD OPEN AND GRADUALLY EJECT NORTHEAST AS AN OPEN WAVE...PERHAPS BREAKING DOWN INTO MULTIPLE SHORTWAVE TROUGHS WHICH COULD CROSS THE REGION. THIS SCENARIO SHOULD SUPPORT SCATTERED TO NUMEROUS SHOWERS/THUNDERSTORMS. SUNDAY...THE ONGOING NORTH TO SOUTH MOISTURE GRADIENT COULD PERSIST...THIS POPS ARE TAPERED FROM LIKELY ACROSS THE SOUTH TO CHANCE NORTH. MONDAY...THE INCREASINGLY ILL-DEFINED MOISTURE GRADIENT SHIFTS TO A WEST/NORTHWEST TO EAST/SOUTHEAST ORIENTATION...AND POPS ARE DISTRIBUTED ACCORDINGLY WITH LIKELY POPS ACROSS CENTRAL/SOUTHERN COASTAL COUNTIES AND ADJACENT COASTAL WATERS. NEAR NORMAL TEMPERATURES ARE EXPECTED THROUGH THE PERIOD...ALTHOUGH LOCALLY COOLER DAYTIME HIGH TEMPS IN THE LOWER/MIDDLE 80S CANNOT BE RULED OUT WHERE PRECIPITATION PERSISTS. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... MANY FORECAST DETAILS DEPEND ON THE HIGHLY UNCERTAIN TRACK AND STRENGTH OF TROPICAL STORM ERIKA NEXT WEEK. AS OF 5 AM EDT...THE NATIONAL HURRICANE CENTER FORECAST SHIFTED A WEAKER SYSTEM FARTHER WEST...RESULTING IN A LANDFALL OVER SOUTHERN FLORIDA AND NOTHING STRONGER THAN A TROPICAL STORM TRACKING NORTH OVER LAND THROUGH EARLY NEXT WEDNESDAY MORNING. ALSO OF NOTE...MOST INVEST TRACKS HAVE ALSO SHIFTED FARTHER WEST...AND OF PARTICULAR INTEREST 28/00Z OPERATIONAL RUNS OF THE GFS AND EUROPEAN DEPICT AN EVEN WEAKER SYSTEM PROGRESSING FARTHER W/NW...PUSHING INTO THE GULF OF MEXICO THEN PERHAPS COMING ASHORE ALONG THE NORTHEAST GULF COAST. THE LATEST FORECAST STILL OFFERS THE POTENTIAL FOR SOME IMPACTS INCLUDING HEAVY RAIN, GUSTY WINDS, MARINE HAZARDS, SHALLOW COASTAL FLOODING AND EVEN A THREAT FOR TORNADOES AROUND THE MIDDLE OF NEXT WEEK. THE GFS/EURO SCENARIO COULD BE ACCOMPANIED BY AN INFLUX OF ENHANCED TROPICAL MOISTURE FROM THE SOUTH/SOUTHEAST BUT OTHERWISE SUGGESTS NO TROPICAL CYCLONE IMPACTS IN OUR FORECAST AREA. ASIDE FROM LOWERING WIND SPEEDS OVER LAND...SIGNIFICANT CHANGES WERE NOT REQUIRED FOR ONGOING WEATHER/POPS GRIDS THROUGH THIS PERIOD. PLEASE CONTINUE TO MONITOR THE LATEST FORECASTS FROM THE NATIONAL HURRICANE CENTER AND OUR OFFICE CONCERNING ERIKA. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/...
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LOW STRATUS AT KSAV HAS HUNG AROUND THROUGH 14Z BUT...BASED ON SATELLITE OBS...CEILINGS ARE EXPECTED TO LIFT AND VFR CONDITIONS TO RETURN RETURN VERY QUICKLY THIS MORNING. TSTMS PROBABILITIES LOOK TOO LOW TO JUSTIFY A MENTION AT EITHER TERMINAL TODAY...ALTHOUGH PROBABILITIES ARE HIGHER AT KSAV. WILL NOT MENTION TSRA WITH THE 12Z TAF CYCLE. EXTENDED AVIATION OUTLOOK...THIS WEEKEND INTO EARLY NEXT WEEK... FLIGHT RESTRICTIONS COULD OCCUR WITH SHOWERS/THUNDERSTORMS AND IN LATE NIGHT/EARLY MORNING STRATUS/FOG. OTHERWISE...MAINLY VFR. TUESDAY AND BEYOND...CONDITIONS REMAIN HIGHLY DEPENDENT ON THE UNCERTAIN TRACK AND INTENSITY OF TROPICAL CYCLONE ERIKA.
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&& .MARINE... TODAY...A BIT OF AN EAST TO NORTHEAST WIND SURGE WILL WORK DOWN THE COAST TODAY. THE STRENGTH OF SURGE IS UNCERTAIN WITH THE LATEST NAM SHOWING WINDS INCREASING TO 15-20 KT FOR THE SOUTH CAROLINA COASTAL WATERS. THIS IS HIGHER THAN ANY GUIDANCE AND IS LIKELY DUE TO THE MODEL/S DEPICTION OF A STRENGTHENING PRESSURE GRADIENT INDUCED BY DEVELOPING LOW PRESSURE WELL OFFSHORE. IT IS UNCLEAR WHETHER THIS LOW WILL DEVELOP OR NOT...BUT THE NAM IS REALLY THE ONLY MODEL SHOWING THIS SIGNAL. WILL THEREFORE DISCOUNT THIS SOLUTION AND BLEND THE VARIOUS SHORT TERM MODELS TO CONSTRUCT WINDS THROUGH THIS AFTERNOON. THIS YIELDS SPEEDS AROUND 15 KT CHARLESTON COUNTY WATERS...10-15 KT BEAUFORT COUNTY WATERS WITH AROUND 10 KT FOR THE GEORGIA WATERS. SEAS WILL AVERAGE 2-4 FT. TONIGHT...THE LOW-LEVEL WIND FIELD WILL RELAX A BIT OVERNIGHT WITH SPEEDS SETTLING IN AROUND 10 KT FOR MUCH OF THE NIGHT OUT OF THE EAST OR NORTHEAST. SEAS WILL AVERAGE 2-4 FT. SATURDAY THROUGH MONDAY...ON THE PERIPHERY OF ATLANTIC HIGH PRESSURE E/NE WINDS DURING THE LATE NIGHT/MORNING HOURS AND E/SE WINDS DURING THE AFTERNOON/EVENING HOURS WILL AVERAGE NO MORE THAN 10-15 KNOTS. SEAS OF 2-4 FT SATURDAY WILL GRADUALLY BUILD MAINLY DUE TO INCREASING LONG PERIOD SWELL FROM THE EAST/SOUTHEAST...AND BY LATE SUNDAY THROUGH MONDAY 6-7 FT SEAS COULD PUSH INTO AMZ374...WITH 4-5 FT SEAS SPREADING INTO NEARSHORE WATERS. MONDAY NIGHT THROUGH MIDWEEK...WINDS/SEAS WILL DEPEND ON THE UNCERTAIN TRACK AND INTENSITY OF TROPICAL STORM ERIKA. BASED ON THE LATEST FORECAST TRACK PUSHING A WEAKER SYSTEM INLAND OVER THE FLORIDA PENINSULA...LOWERED WINDS/SEAS OVER COASTAL WATERS DURING THIS PERIOD. HOWEVER...WINDS/SEAS COULD STILL BECOME HAZARDOUS FOR SMALL CRAFT. PLEASE STAY TUNED TO THE LATEST FORECASTS FROM THE NATIONAL HURRICANE CENTER AND OUR OFFICE CONCERNING ERIKA. RIP CURRENTS...SLOWLY BUILDING EAST/SOUTHEAST SWELL COMBINED WITH INCREASING COASTAL WINDS WILL SUPPORT A MODERATE RISK FOR RIP CURRENTS FOR ALL BEACHES TODAY. A PERSISTENT LONG PERIOD SWELL... ONSHORE WINDS AND ASTRONOMICAL INFLUENCES WILL LIKELY SUPPORT AN ELEVATED RISK OF RIP CURRENTS THIS WEEKEND. IF TROPICAL CYCLONE ERIKA APPROACHES THE REGION NEXT WEEK...DANGEROUS RIP CURRENTS COULD DEVELOP ON AREA BEACHES. && .TIDES/COASTAL FLOODING... THIS EVENING...EXPECT POSITIVE TIDAL ANOMALIES TO INCREASE TODAY AS STRENGTHENING EAST TO NORTHEAST WINDS HELP TO PILE WATER INTO THE SOUTH CAROLINA AND GEORGIA COAST. EARLY MORNING SURGE GUIDANCE BRINGS TIDE LEVELS TO SHALLOW COASTAL FLOODING THRESHOLDS AT BOTH THE CHARLESTON HARBOR AND FORT PULASKI TIDE GAGES...BUT THE FORECASTED LEVELS LOOK A BIT TOO HIGH GIVEN PREVIOUS TIDAL TRENDS AND EXPECTED WIND SPEEDS. EVEN AFTER COMPENSATING FOR THIS...TIDE LEVELS AT THE CHARLESTON HARBOR ARE STILL EXPECTED TO PEAK 7.0-7.2 FT MLLW SO WILL GO AHEAD AND HOIST A COASTAL FLOOD ADVISORY FOR ALL OF THE SOUTH CAROLINA COASTAL ZONES...VALID FROM 6PM-10PM TONIGHT. LEVELS AT FORT PULASKI ARE EXPECTED TO ONLY PEAK 9.0-9.2 FT MLLW...WHICH IS AT OR JUST BELOW COASTAL FLOOD ADVISORY CRITERIA FOR COASTAL GEORGIA. CONFIDENCE IS THEREFORE NOT HIGH ENOUGH TO JUSTIFY THE ISSUANCE OF A COASTAL FLOOD ADVISORY FOR ANY PORTION OF THE GEORGIA COAST WITH THIS FORECAST CYCLE. TIDE TRENDS WILL BE MONITORED CAREFULLY THROUGHOUT THE DAY. SATURDAY THROUGH MONDAY...ASTRONOMICAL INFLUENCES AND ONSHORE WINDS WILL MAINTAIN ELEVATED HIGH TIDE LEVELS. THE EVENING HIGH TIDES ARE FORECAST TO EXCEED SHALLOW COASTAL FLOODING LEVELS ON CHARLESTON HARBOR AND SHOULD AT LEAST APPROACH COASTAL FLOOD ADVISORY THRESHOLDS FARTHER SOUTH INCLUDING THE GEORGIA COAST. ON CHARLESTON HARBOR...EVEN THE MORNING HIGH TIDES ARE FORECAST TO APPROACH 7 FEET MEAN LOWER LOW WATER EACH DAY. TUESDAY THROUGH WEDNESDAY/THURSDAY...ASTRONOMICAL INFLUENCES WILL WANE. HOWEVER...IF THE LATEST FORECAST FROM NHC FOR ERIKA HOLDS...WE WILL HAVE THE POTENTIAL FOR MORE SIGNIFICANT RISES IN THE TIDES ALONG WITH SOME DEGREE OF COASTAL FLOODING. WITH REGARDS TO POTENTIAL CONDITIONS NEXT WEEK...PLEASE STAY TUNED TO THE LATEST FORECASTS FROM THE NATIONAL HURRICANE CENTER AND OUR OFFICE CONCERNING ERIKA. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...COASTAL FLOOD ADVISORY FROM 6 PM TO 10 PM EDT THIS EVENING FOR SCZ048>051. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...CEB/ST SHORT TERM...SPR LONG TERM...SPR AVIATION...CEB/ST MARINE...ST TIDES/COASTAL FLOODING...

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