Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 310909
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
509 AM EDT MON AUG 31 2015

.SYNOPSIS...
A STRONG UPPER LEVEL DISTURBANCE ACROSS GEORGIA WILL MOVE NORTH
AND WEAKEN TONIGHT. ON THE PERIPHERY OF ATLANTIC HIGH PRESSURE...A
WEAK TROUGH OF LOW PRESSURE WILL MEANDER OVER THE SOUTHEAST MOST
OF THIS WEEK. LATE THIS WEEK INTO NEXT WEEKEND...LOW PRESSURE WILL
DEVELOP OVER THE ATLANTIC WHILE WEAK INLAND HIGH PRESSURE EXPANDS
SOUTH AND EAST INTO THE REGION.

&&

.NEAR TERM /THROUGH TONIGHT/...
FLOODING CONCERNS UNDERWAY ALONG AND EAST OF I-95 AS RAINFALL EXPANDS
DUE TO THE SHARPENING OF A SURFACE TROUGH NEAR THE COAST AND
INTENSIFYING LOW LEVEL SPEED CONVERGENCE...ENHANCED BY HIGH PWAT
VALUES AND A RIBBON OF UPPER LEVEL DIFLUENCE AND MID LEVEL OMEGA
ALONG THE TAIL OF THE EJECTING UPPER WAVE ACROSS THE WESTERN
CAROLINAS. IT LOOKS AS IF THE SEVERE WEATHER THREAT HAS DIMINISHED
AS LATEST ANALYSIS SHOWS BETTER SHEAR PARAMETERS MOVING UP INTO
THE PEE DEE REGION.

WITH THE ONGOING PULSE OF EXPANDING RAINFALL AND TRAINING ALONG THE
I-95 CORRIDOR WE EXPECT THE EVENT TO PEAK LATER THIS MORNING AND
WITH ONGOING FLOOD ADVISORIES/WARNINGS. LOCALIZED FLOODING DOES
APPEAR TO BE A GOOD BET THIS MORNING...ESPECIALLY ACROSS SOUTHEAST
SOUTH CAROLINA.

FAR INLAND AREAS LIKELY TO REMAIN DRY WITH SOME PATCHY/AREAS OF FOG
AS DRIER AIR AND SUBSIDENCE ADVECTS FROM THE SW IN THE WAKE OF THE
EJECTING UPPER LOW.

WIDESPREAD RAINS AND FEW TSTMS ALONG AND EAST OF I-95 ARE EXPECTED
TO SHIFT NE AND OFFSHORE LATE MORNING AND CERTAINLY BY THIS
AFTERNOON. LOCALIZED FLASH FLOODING IS POSSIBLE GIVEN THE ONGOING
SITUATION PRE-DAWN. IF RAINS ARE STILL ONGOING AROUND HIGH TIDE
AT MID MORNING...THEN COASTAL COUNTIES ARE IN RISK FOR EXACERBATED
FLOODING AS ASTRONOMICAL TIDE CYCLES ARE ALREADY HIGH AND COASTAL
FLOODING WITHOUT ANY RAINS IS EXPECTED. IN DOWNTOWN CHARLESTON...
THERE IS A SIGNIFICANT CONCERN THAT TO NEED TO WATCHING HOUR BY
HOUR NEARING HIGH TIDE. DOWNTOWN SAVANNAH...THE CONCERN BY HIGH
TIDE APPEARS LESS GIVEN LATEST TIMING PROGS FROM VARIOUS HIGH
RESOLUTION MODEL OUTPUTS.

SINCE I-95 CORRIDOR SEPARATES CATEGORICAL FROM MUCH LESSES CHANCES
TO THE WEST THIS MORNING...WE SLOWLY DIMINISH POPS AS A LOW PRES
WAVE LIFTS UP THE COAST. THE ENVIRONMENT AFTER THE LOW WILL BE
FAIRLY BENIGN FOR A LOT ADDITIONAL CONVECTIVE DEVELOPMENT ACROSS
SE GEORGIA AS SOME AFTERNOON CLEARING OCCURS. WE BUMPED HIGH
TEMPS UP MANY AREAS THIS AFTERNOON AS SOME SUNSHINE BREAK OUT.

TONIGHT...A MUCH QUIETER NIGHT IS EXPECTED WITH PARTLY CLOUDY
SKIES FOR MOST AREAS. AN EXCEPTION COULD BE ACROSS SE GEORGIA
AS SCATTERED SHOWERS REDEVELOP AS DEEP MOISTURE INCREASES
AND A MID LEVEL VORT AXIS POKES NORTH FROM FLORIDA.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
TUESDAY THROUGH THURSDAY...AN UPPER RIDGE WILL BUILD OVER THE REGION
FROM THE SOUTHEAST. HOWEVER...VORTICITY/ASSOCIATED ENHANCED MOISTURE
TRAPPED WITHIN THE RIDGE WILL DRIFT OVER THE SOUTHEAST AND WILL
CONTRIBUTE TO SCATTERED SHOWERS/THUNDERSTORMS ESPECIALLY MIDDAY INTO
THE EVENING. PER 850-500 MB MOISTURE PROGS...HIGHEST PM POP ARE
FOCUSED ACROSS SOUTHERN COUNTIES...BUT THE NORTH/SOUTH POPS GRADIENT
REMAINS SUBTLE. ALSO...GUIDANCE DIFFERS REGARDING THE
TRACK/ORIENTATION OF VORTICITY...IN PART PROVIDED BY THE REMNANTS OF
ERIKA...AND THIS WILL IMPACT DAY TO DAY POP TRENDS. FOR
NOW...SLIGHTLY GREATER AFTERNOON/EVENING POPS ARE IN PLACE FOR
WEDNESDAY...AS HIGH AS 40-50 PERCENT...AS COMPARED WITH TUESDAY AND
THURSDAY. DESPITE THE PREVALENCE OF CLOUDS...DAYTIME HIGHS SHOULD
RECOVER INTO THE UPPER 80S/LOWER 90S EACH DAY.

EACH NIGHT...POPS SHOULD DIMINISH OVER LAND/AWAY FROM THE IMMEDIATE
COAST PER TYPICAL DIURNAL TRENDS...WHILE POPS COULD INCREASE OVER
COASTAL WATERS EACH NIGHT. LOW TEMPERATURES IN THE 70S WILL REMAIN
COMMON EACH NIGHT.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
A LONGWAVE UPPER TROUGH IS PROGGED TO ADVANCE INTO THE REGION FROM
THE WEST LATE THIS WEEK. THEN...THIS FEATURE COULD BECOME CUT-OFF
OVER THE SOUTHEAST AS A BLOCKING PATTERN DEVELOPS NEXT WEEKEND
THROUGH EARLY NEXT WEEK. MEANWHILE...HIGH PRESSURE WILL GRADUALLY
BUILD INTO THE REGION FROM THE NORTH...PRODUCING A PERSISTENT/LONG
FETCH ONSHORE FLOW. BY LATE WEEKEND/EARLY NEXT WEEK...A COASTAL
TROUGH COULD DEVELOP. THIS PATTERN SHOULD SUPPORT UNSETTLED
CONDITIONS...JUSTIFYING AT LEAST CHANCE POPS DURING THE DAY AND
PERSISTENT NIGHTTIME POPS ESPECIALLY NEAR THE COAST AND ACROSS
ADJACENT COASTAL WATERS...AS WELL SLIGHTLY COOLER HIGH TEMPERATURES
IN THE MID TO UPPER 80S.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
VERY CHALLENGING TAFS THIS MORNING DUE TO THE POTENTIAL FOR LOW
STRATUS AND/OR FOG AND PINNING DOWN THE RAIN CHANCES. BEST CHANCE
FOR PRECIPITATION AT KSAV LOOKS TO BE THROUGH DAYBREAK AFTER
WHICH THE BEST FORCING SHIFTS EAST. VSBYS WILL BRIEFLY BE REDUCED
DURING SHOWERS...POTENTIALLY IFR AT TIMES. ONCE PRECIP ENDS THERE
WILL BE AN INCREASING CHANCE FOR STRATUS BUILD-DOWN AND POSSIBLE
FOG AS EXTENSIVE MOISTURE LINGERS IN LOW-LEVELS AROUND DAWN. WE
MAINTAINED IFR VSBY/CEILING LATE TONIGHT THROUGH MON MORNING WITH
VFR RETURNING AFTER MID MORNING.

AT KCHS...PRECIP FLARING UP THIS MORNING AND EXPECT THOUGH
COVERAGE WILL PROBABLY BE LESS LATE. MVFR CEILINGS/VSBY WILL
BECOME INCREASINGLY LIKELY OVERNIGHT...ESPECIALLY LATER ONCE THE
COASTAL TROUGH TIGHTENS AND A WEAK LOW STARTS MOVING UP THE COAST.
CONDITIONS SHOULD IMPROVE LATE MON MORNING.

EXTENDED AVIATION OUTLOOK THROUGH FRIDAY...MAINLY VFR. BRIEF FLIGHT
RESTRICTIONS COULD OCCUR MAINLY WITHIN SHOWERS/THUNDERSTORMS.

&&

.MARINE...
WE HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE CHARLESTON COUNTY
WATERS TODAY...MAINLY FOR SEAS TOUCHING NEAR 6 FT CLOSER TO 15-20
NM OFFSHORE. A SMALL CRAFT ADVISORY FOR THE OUTER GEORGIA WATERS
ALSO CONTINUES TODAY.

A WEAK WAVE OF LOW PRES WILL MOVE UP ALONG THE I-95 CORRIDOR TODAY
AND THIS SHOULD ALLOW ONSHORE FLOW TO BECOME S OR SW AND SPEEDS
WILL ALSO DIMINISH LATER TODAY. ELEVATED SEAS WILL DIMINISH
TONIGHT AS THE FLOW BECOMES SOMEWHAT VARIABLE FROM NORTH TO SOUTH.

SHOWERS AND TSTMS WILL LOWER VSBYS BELOW 3 NM AT TIMES THROUGH
AT LEAST MIDDAY.

TUESDAY THROUGH SATURDAY. A WEAK PRESSURE PATTERN WILL TRANSLATE TO
WINDS/SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH THIS
PERIOD. WINDS WILL REMAIN DOMINATED BY THE SEA BREEZE EACH
AFTERNOON/EVENING AND BY THE LAND BREEZE EACH OVERNIGHT/EARLY
MORNING...MAINLY LESS THAN 15 KT THROUGH THE PERIOD. SEAS WILL OF
2-4 FT TUESDAY WILL SUBSIDE TO 1-3 FT WEDNESDAY THROUGH LATE WEEK.
CONDITIONS COULD BEGIN TO DETERIORATE AS HIGH PRESSURE BUILDS FROM
THE NORTH NEXT WEEKEND.

RIP CURRENTS... AN ELEVATED RISK FOR RIP CURRENTS COULD PERSIST
TUESDAY. AN ELEVATED RISK FOR RIP CURRENTS COULD DEVELOP AGAIN NEXT
WEEKEND.

&&

.TIDES/COASTAL FLOODING...
WE HAVE ISSUED A COASTAL FLOOD ADVISORY ALONG THE SOUTH CAROLINA
COAST EARLY THIS MORNING AS ONSHORE FLOW STILL GOING STRONG AND
EXPECTATIONS OF A HIGH TIDE JUST ABOVE 7 FT MLLW AT DOWNTOWN
CHARLESTON. A GREATER CONCERN WILL BE WHETHER HEAVY RAINS ARE
STILL ONGOING AROUND 9 OR 10 AM THIS MORNING. IF HEAVY RAIN
FALLS IN DOWNTOWN CHARLESTON AND/OR DOWNTOWN SAVANNAH AROUND THE
TIME OF HIGH TIDE...MORE SIGNIFICANT FLOODING IS POSSIBLE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...COASTAL FLOOD ADVISORY FROM 8 AM THIS MORNING TO NOON EDT
     TODAY FOR SCZ048>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR AMZ350.
     SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...SPR
TIDES/COASTAL FLOODING...


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