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FXUS62 KCHS 241453
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1053 AM EDT FRI OCT 24 2008
.SYNOPSIS...
LOW PRES WILL TRACK NE FROM THE GULF OF MEXICO OVER THE REGION
THIS AFTERNOON THROUGH TONIGHT. HIGH PRES WILL BUILD BACK IN FOR
THE WEEKEND...THEN A COLD FRONT WILL CROSS THE AREA LATE MON.
ANOTHER HIGH PRES WILL BUILD IN FOR THE MIDDLE AND LATTER PORTION
OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE FRIDAY MORNING SURFACE ANALYSIS FEATURED CLASSIC WEDGE
SCENARIO...WITH HIGH PRESSURE OVER LAND...LOW PRESSURE EMERGING
FROM THE NORTHERN GULF OF MEXICO AND AN ASSOCIATED WARM FRONT
EXTENDING NE ACROSS THE COASTAL WATERS. MEANWHILE...THE PARENT
UPPER LOW WAS CENTERED JUST WEST OF THE MS RIVER VALLEY. THIS
FEATURE WAS DRAWING DEEP MOISTURE NORTH ACROSS THE FORECAST
AREA...AND FORCING/ASCENT WAS ENHANCED BY A 80-120 KNOT 300-200
MB JET CORE ROUNDING THE BASE OF THIS FEATURE. AS A RESULT...
OVERRUNNING RAIN HAD SPREAD ACROSS THE ENTIRE FORECAST AREA.
WHILE THE SYNOPTIC RAIN SHIELD WAS ADVANCING NE...LOW TOPPED
CONVECTIVE ELEMENTS WERE NOTED ACROSS THE COASTAL WATERS...CLOSE
TO THE WARM FRONT/COASTAL TROUGH...PUSHING NW TOWARD COASTAL
COUNTIES.
WIDESPREAD...PRIMARILY STRATIFORM RAIN/CATEGORICAL POPS WILL
CONTINUE THROUGH MOST OF THIS AFTERNOON. RAIN WILL BE HEAVY AT
TIMES...AS PWATS WILL INCREASE INTO THE 1.5 TO 2 INCH RANGE...AND
DAYTIME STORM TOTAL RAINFALL AMOUNTS OF 1 TO 3 INCHES WILL BE
COMMON. THEN...BY LATE AFTERNOON...THE SURFACE LOW WILL ADVANCE NE
AND WILL PULL THE WARM SECTOR INTO S/E COUNTIES OF THE FORECAST
AREA...AS PROGRESSIVE DRY SLOT NOTED ON WATER VAPOR IMAGERY SWEEPS
INTO THE REGION FROM THE SW. THUS...PRECIPITATION WILL TRANSITION
FROM PRIMARILY STRATIFORM TO PRIMARILY CONVECTIVE BY LATE
AFTERNOON/EARLY EVENING.
LAKE WINDS...MAINTAINED THE ONGOING THE LAKE WIND ADVISORY GIVEN
BOUNDARY LAYER WINDS INCREASING TO 25 TO 30 KT TODAY.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
THE DRY SLOT AND N MOMENTUM OF THE SURFACE LOW SHOULD CUT THE RAIN
OFF QUICKLY THIS EVENING IS SE GEORGIA BUT THE MOST CONCERN
THROUGH MIDNIGHT WILL BE ALONG THE CENTRAL SOUTH CAROLINA COAST
PRIOR TO MIDNIGHT AS THE MAIN SURFACE LOW MAY POSSIBLY MOVE W OF
CHARLESTON ALLOWING A GATE OF INSTABILITY AND A HIGHLY SHEARED
WIND ENVIRONMENT TO MAKE A RUN FOR COASTAL AREAS. THIS WILL NEED
TO BE MONITORED CLOSELY FOR SEVERE WEATHER POTENTIAL...ESPECIALLY
GIVEN HIGH HELICITY VALUES SUPPORTING THE POTENTIAL FOR LOW TOPPED
SUPERCELLS PRODUCING DAMAGING WIND GUSTS AND EVEN ISOLATED
TORNADOES. WE HAVE CONTINUED TO MENTION A SLIGHT CHANCE OF TSTMS
IN THIS AREA THIS EVENING. AFTER MIDNIGHT... MOST OF THE ACTION
SHOULD SHIFT N AND NE AWAY FROM THE FORECAST AREA. WITH A WEAK
PRES REGION PRIOR TO THE BACK- SIDE FRONTAL PASSAGE...LOW CLOUDS
AND AREAS OF FOG WILL LIKELY BE FOUND. SINCE TIMING ISSUES
REMAIN...WE HAVE INTRODUCED ONLY PATCHY FOG TO THE ZONES W OF I-95
TO TREND THIS MORNING.
LAKE WINDS...HIGHEST WINDS ACROSS LAKE MOULTRIE THIS EVENING WILL
DROP OFF THROUGH THE OVERNIGHT HOURS AS SURFACE LOW MOVES INTO THE
AREA AND PULLS AWAY LATE. WE WILL KEEP A MARGINAL LAKE WIND
ADVISORY IN EFFECT EARLY...BUT WINDS WILL GRADUALLY DROP OFF
OVERNIGHT AS THE LOW LIFTS NORTHWARD.
CLEARING SKIES AND WARMER TEMPERATURES IN THE MID TO UPPER 70S WITH
DOWNSLOPING DEVELOPING ON SAT. THE LAST TO CLEAR WILL PROBABLY BE
IN THE CHARLESTON TRI-COUNTY AREA...BUT MOST AREAS SHOULD SEE
AMPLE SUNSHINE BY EARLY AFTERNOON. MAINLY CLEAR SKIES SAT NIGHT
WITH LIGHT WINDS AND LOWS UPPER 40S TO LOWER 50S.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
A WEAK PRES PATTERN ON SUNDAY WITH A WEAK LEE-SIDE SURFACE TROF
BY EARLY MON ALONG WITH A DEEP AND DRY ATMOSPHERIC COLUMN. THIS
WILL RESULT IN MAINLY CLEAR SKIES AND SLIGHTLY ABOVE NORMAL HIGH
TEMPERATURES WITH AN OCCASIONAL DOWNSLOPE COMPONENT TO THE SURFACE
WINDS IN THE MORNING HOURS.
GLOBAL MODELS CONTINUE TO ADVERTISE A DEEP UPPER LEVEL TROF WILL
DEVELOP ALONG THE EAST COAST LATE MON INTO EARLY TUE. A COLD FRONT
ASSOCIATED WITH THIS FEATURE IS EXPECTED TO MOVE THROUGH THE AREA
LATE MON. LIMITED MOISTURE SHOULD PRECLUDE THE THREAT FOR ANY
PRECIPITATION AND IN ALL LIKELIHOOD THERE WILL NOT BE EVEN MUCH
CLOUDINESS ASSOCIATED WITH THE FRONT.
BEHIND THE FRONT MUCH COLDER AIR WILL MOVE INTO THE AREA AND
SOME CHANCE FOR FROST IS POSSIBLE INLAND EARLY TUE IF SUBSTANTIAL
LATE NIGHT DECOUPLING OCCURS. THE UPPER TROF LOOKS TO PULL OUT
VERY QUICK BUT WE DID NOT RAISE MIN TEMPERATURES ON WED MORNING AS
EXCELLENT RADIATIONAL CONDITIONS SEEM LIKELY. HIGH TEMPERATURES
UNDER PLENTY OF SUNSHINE WILL MAINLY BE IN THE MID OR UPPER 60S
THROUGH MID WEEK.
&&
.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
THE LOWER CIGS HAVE FINALLY REACHED KSAV...WHERE WE HAVE
INITIALIZED WITH MVFR CONDITIONS...BUT HAVE MAINTAINED VFR WEATHER
AT KCHS TIL 15Z. CONDITIONS WILL CONTINUE TO FURTHER DETERIORATE
THROUGH THE FORECAST PERIOD...WITH PREVAILING MVFR AND EVENTUALLY
IFR CONDITIONS TO PERSIST THROUGH 12Z SATURDAY WITH PERIODS OF
RAIN AND SHRA. HEAVIEST RAINS LOOK TO OCCUR FROM 15Z-22Z AT
KSAV...AND BETWEEN 17Z TODAY AND 02Z SATURDAY AT KCHS. AS THE
RAINS TAPER OFF TONIGHT...FOG FORMATION WILL OCCUR...AND WE COULD
EXPERIENCE A FEW HOURS OF LIFR CONDITIONS...ESPECIALLY AT KSAV.
GIVEN THAT THE LOW FROM THE GULF OF MEXICO WILL TRACK NE AND PASS
NEAR BOTH TERMINALS THE FIRST PART OF TONIGHT...WE WILL NEED TO
KEEP WATCH FOR ISOLATED ELEVATED CONVECTION. HOWEVER...PROBABILITIES
OF THIS OCCURRENCE IS TOO LOW TO INCLUDE WITH THE 12Z TAFS.
NE SURFACE WINDS REMAIN NEAR 10 KT THIS MORNING...WHILE WINDS AT
2K FT ARE MORE EASTERLY AND AROUND 30 KT. AS A RESULT WE HAVE
INCLUDED A FEW HOURS OF WIND SHEAR AT BOTH SITES THROUGH 15Z. AS
SURFACE WINDS BEGIN TO INCREASE BY AFTERNOON...THE RISK OF WIND
SHEAR DROPS OFF...BUT PILOTS ARE ADVISED THAT WINDS AT 1K=2K FT
ARE STILL CLOSE TO 30 OR 35 KT. WIND SHEAR WILL AGAIN FORM THIS
EVENING AS SURFACE WINDS DROP OFF...BUT WINDS AT 2K FT REMAIN
ELEVATED.
EXTENDED AVIATION OUTLOOK...MVFR AND/OR IFR CONDITIONS WILL PREVAIL
THROUGH THE FIRST PART OF SATURDAY. VFR CONDITIONS WILL RETURN
LATE SATURDAY AND WILL CONTINUE THROUGH TUESDAY.
&&
.MARINE...
THE ONGOING HAZARDOUS MARINE EVENT WILL CONTINUE TODAY INTO
TONIGHT...WITH GALES ACROSS ALL ATLC WATERS...AND SOLID SCA IN
CHARLESTON HARBOR.
COASTAL WARM FRONT IS FOUND ORIENTED NE TO SW ACROSS THE COASTAL
WATERS FRIDAY MORNING...FROM WEST OF GRAYS REEF 41008/ TO JUST
EAST OF THE 40 MILE BUOY /41004/. THIS WARM FRONT WILL SLOWLY LIFT
NW TODAY AS LOW PRES NOW IN THE NE GULF OF MEXICO MOVES ACROSS THE
FL PANHANDLE AND NORTH FL BY LATE IN THE DAY. THERE IS STILL SOME
UNCERTAINTY REGARDING THE EXACT TRACK THE LOW WILL TAKE AS IT
MOVES OVER LAND...BUT BEST FORECAST AT THIS TIME TAKES THE LOW
INTO SE GA EARLY TONIGHT...THEN INTO SOUTHERN SC AFTER
MIDNIGHT...BEFORE LIFTING NORTH AND AWAY FROM THE AREA LATE
TONIGHT. STRONG PINCHING OF THE PRES GRADIENT BETWEEN THE HIGH
PRES WEDGE AND THE LOW TODAY WILL RESULT IN A CONTINUATION OF
GALES OVER THE ATLC WATERS. WINDS IN CHARLESTON HARBOR WILL REACH
25 TO 30 KT. WILL CONTINUE TO ASSESS THE POTENTIAL FOR A PERIOD OF
GALE FORCE GUSTS ON THE HARBOR LATER TODAY INTO THIS EVENING.
AS THE LOW LIFTS NORTHWARD TONIGHT THERE DOES LOOK TO BE SOME
RELAXATION IN THE PRES GRADIENT...THUS OUR GALES WILL COME DOWN.
HOWEVER...A SLOWER PROGRESSION OF THE LOW NORTHWARD...OR A DEEPER
LOW COULD RESULT IN A LONGER PERIOD OF GALES OVER AMZ350. EVEN
SO...SCA/S WILL NEED TO BE HOISTED ONCE THE GALES COME TO AN END.
SEAS WILL EASILY REACH AS HIGH AS 8 OR 9 FT ON THE WATERS WITHIN 20
NM OF THE COAST TODAY INTO TONIGHT...WITH DOUBLE DIGIT VALUES ACROSS
THE OUTER GA WATERS.
AS THE SURFACE LOW LIFTS NORTH A TRAILING COLD FRONT WILL SHIFT
EASTWARD AND PASS THROUGH THE LOCAL WATERS SATURDAY MORNING. THIS
WILL SHIFT WINDS TO AN OFFSHORE FETCH AND ALLOW FOR A GRADUAL
DECREASE IN BOTH WINDS AND SEAS...AS HIGH PRES BUILDS FROM THE WEST.
A FURTHER DECREASE IN WINDS/SEAS WILL DEVELOP FOR SUNDAY INTO EARLY
MONDAY...BUT THE NEXT COLD FRONT BY LATE MONDAY WILL BE FOLLOWED BY
AN INCREASE OF WINDS/SEAS ONCE AGAIN...AND WE COULD BE LOOKING AT
MARGINAL SCA/S...ESPECIALLY ACROSS THE OUTER GA WATERS WITHIN THE
RESULTING COLD AIR ADVECTION IN WAKE OF THE FRONT.
RIP CURRENTS...STRONG ONSHORE WINDS AND SMALL SWELLS WILL LEAD TO A
HIGH RISK OF RIP CURRENTS AT AREA BEACHES TODAY.
&&
.TIDES/COASTAL FLOODING...
ALTHOUGH TIDE LEVELS HAVE BEEN AND WILL CONTINUE TO BE WELL ABOVE
PREDICTED LEVELS THIS MORNING...DEPARTURES WILL ONLY REACH AROUND 1
FOOT ABOVE WITH THE UPCOMING HIGH TIDE AROUND 5-6 AM. THIS WOULD
RESULT IN TIDES REACHING AROUND 6.7 OR 6.8 FT MLLW IN CHARLESTON AND
8.4 OR 8.5 FT MLLW AT FORT PULASKI/SAVANNAH. THIS IS JUST BELOW ANY
SHALLOW COASTAL FLOODING CRITERIA...THUS WE WILL HOLD OFF ON A
COASTAL FLOOD ADVISORY FOR THE NEXT HIGH TIDE. HOWEVER...DEPARTURES
WILL BE A BIT HIGHER WITH THE LATE DAY HIGH TIDE...AND THAT ALONG
WITH THE CONTINUED STRONG ONSHORE WINDS...ELEVATED SURF AND PERIODS
OF HEAVY RAIN HAVE PROMPTED US TO ISSUE A COASTAL FLOOD ADVISORY FOR
THE HIGH TIDE AROUND 5 TO 6 PM.
EASTERLY FETCH IS KEEPING SEAS ELEVATED ACROSS THE SE GA AND FAR
SOUTHERN SC WATERS EARLY THIS MORNING...AND WITH GALE FORCE WINDS TO
CONTINUE OVER THE ATLC...SEAS WILL NOT COME DOWN ANY TIME SOON. THUS
WE WILL CONTINUE TO EXPERIENCE AT LEAST 5 FOOT BREAKERS IN THE SURF
ZONE TODAY...AND WE HAVE MAINTAINED OUR HIGH SURF ADVISORY. WITH
TIME THE FETCH ACROSS THE NORTHERN SC WATERS WILL BECOME EASTERLY BY
LATE TODAY AND INTO TONIGHT. THIS IN TURN WILL ALLOW FOR A FURTHER
INCREASE IN SEAS OVER THE CHARLESTON AND COLLETON COUNTY
COASTLINE...AND BREAKERS WILL ALSO REACH 5 FT FROM LATE TODAY
THROUGH TONIGHT. AS A RESULT WE HAVE RAISED A HIGH SURF ADVISORY
FURTHER NORTH...BEGINNING AT 5 PM.
GIVEN THE ELEVATED TIDES...ROUGH SURF...STRONG ONSHORE WINDS AND
PERIODS OF HEAVY RAIN TODAY INTO EARLY TONIGHT...AT LEAST MINOR
BEACH EROSION WILL ALSO OCCUR.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HIGH SURF ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR GAZ117-119-
139-141.
COASTAL FLOOD ADVISORY FROM 4 PM THIS AFTERNOON TO 8 PM EDT
THIS EVENING FOR GAZ117-119-139-141.
SC...HIGH SURF ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR SCZ048-051.
COASTAL FLOOD ADVISORY FROM 4 PM THIS AFTERNOON TO 8 PM EDT
THIS EVENING FOR SCZ048>051.
LAKE WIND ADVISORY UNTIL 11 PM EDT THIS EVENING FOR SCZ045.
HIGH SURF ADVISORY FROM 5 PM THIS AFTERNOON TO 6 AM EDT
SATURDAY FOR SCZ049-050.
MARINE...GALE WARNING UNTIL MIDNIGHT EDT TONIGHT FOR AMZ350-352-374.
GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR AMZ354.
SMALL CRAFT ADVISORY UNTIL 5 AM EDT SATURDAY FOR AMZ330.
&&
$$