Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 291152
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
752 AM EDT SAT AUG 29 2015

.SYNOPSIS...
A STALLED FRONT TO THE SOUTH OF THE AREA WILL LIFT NORTH TONIGHT
BUT GRADUALLY DISSIPATE LATE. UPPER LEVEL LOW PRESSURE WILL PASS
INLAND SUNDAY...THEN ATLANTIC HIGH PRESSURE WILL EXPAND INTO THE
REGION MONDAY THROUGH TUESDAY. MID TO LATE WEEK...THE REMNANTS OF
TROPICAL STORM ERIKA COULD DRIFT NORTHEAST OR MEANDER OVER OR
CLOSE TO THE REGION. REFER TO THE LATEST ADVISORY ON ERIKA ISSUED
BY THE NATIONAL HURRICANE CENTER.

&&

.NEAR TERM /THROUGH TONIGHT/...
NEAR-DAWN...WE RAISED POPS TO CATEGORICAL THIS MORNING ACROSS
MCINTOSH COUNTY GEORGIA...OTHERWISE NO SIGNIFICANT CHANGES TO
THE SUNRISE UPDATE. STRONG LEVEL MOISTURE CONVERGENCE FOCUSED
ALONG SOUTH COASTAL GEORGIA THROUGH AT LEAST MID MORNING SHOULD
WEAKEN BY LATE MORNING AS LAND AREAS BEGIN TO WARM.

DEEP LAYERED MOISTURE ADVECTION SHOULD CONTINUE ACROSS SE GEORGIA
TODAY WHILE A WEAK WEDGED SURFACE PATTERN PERSISTS TO THE NORTH
ACROSS MUCH OF SOUTH CAROLINA. SHOWER COVERAGE SHOULD INCREASE
LATE MORNING THROUGH THE AFTERNOON HOURS ACROSS SE GEORGIA DESPITE
ONLY MODEST THERMODYNAMICS ON TAP GIVEN THE WIDESPREAD CLOUDINESS.
MUCH OF THE CONVECTION RAINS CLOSE TO THE COAST COULD REMAIN A
SHALLOW WARM-RAIN PROCESS WITH NOT MUCH THUNDER THIS MORNING. AS
PWATS REMAIN JUST OVER 2 INCHES...THERE IS A DECENT POTENTIAL FOR
LOCALIZED DOWNPOURS AND SOME TSTM ACTIVITY...ESPECIALLY DURING
DIURNAL HEATING JUST ABOUT ANYWHERE ACROSS SE GEORGIA. WE HAVE
SOLID LIKELY POPS ACROSS SE GEORGIA TODAY AND INCLUDED SOUTHERN
JASPER AND BEAUFORT COUNTIES IN THE LIKELY POP SCHEME.

DIMINISHING PCPN RETURNS NORTHWARD AND IT SHOULD REMAIN MAINLY DRY
ALONG ZONES BORDERING THE CSRA AND SE MIDLANDS...WE HAVE ONLY SLIGHT
CHANCE POPS IN THIS REGION. ALONG THE CHARLESTON COUNTY SEA BREEZE...
WE COULD SEE A FEW SHOWERS CROP UP THIS AFTERNOON...POPS IN THE 20/30
PERCENT RANGE.

TONIGHT...MODELS IN GOOD AGREEMENT ON LOFTING DEEP MOIST NORTHWARD
AND WE ANTICIPATE SHOWER CHANCES TO INCREASE NORTHWARD AFTER 2 AM.
A FEW TSTMS ARE ALSO POSSIBLE AS INSTABILITY APPEARS TO INCREASE AS
THE CORE OF THE MID LEVEL LOW ACROSS THE NORTHERN GULF COAST
REGION SHIFTS NE INTO ALABAMA AND THE NW FLORIDA PANHANDLE LATE.
THIS SHOULD ENSURE INCREASING RAIN CHANCES NEARING DAWN. LOW
LEVEL MOISTURE CONVERGENCE PROGS SUGGEST THERE COULD BE SOME
DOWNPOURS ALONG COASTAL ZONES AFTER MIDNIGHT.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
SUNDAY THROUGH MONDAY...THE CLOSED UPPER LOW CENTERED OVER THE
NORTHERN GULF OF MEXICO WILL OPEN AND EJECT NORTHEAST ALONG THE
APPALACHIANS. SUNDAY AND SUNDAY NIGHT...THIS FEATURE WILL PROMOTE
INCREASED/FOCUSED LOW/MID LEVEL MOISTURE TRANSPORT AND WILL DRAW A
PLUME OF DEEP-LAYERED MOISTURE FEATURING PWATS EXCEEDING 2 INCHES
INTO THE REGION. MEANWHILE...MODEST FORCING FOR ASCENT AS DEPICTED
BY 500-300 MB Q VECTOR CONVERGENCE AND 400-200 MB DIVERGENCE WILL
CROSS THE REGION SUNDAY INTO SUNDAY NIGHT. THUS...AT LEAST NUMEROUS
SHOWERS/SCATTERED THUNDERSTORMS WILL CROSS THE REGION SUNDAY...AND
LIKELY POPS ARE JUSTIFIED AT SOME POINT ACROSS THE ENTIRE REGION.
LATER SUNDAY...DRY SLOTTING COULD SPREAD INTO THE REGION FROM THE
SOUTHWEST...AND POPS COULD DECREASE ACROSS SOUTHERN/INLAND COUNTIES.

PWATS EXCEEDING 2 INCHES...FORCING FOR ASCENT AND THE POTENTIAL FOR
TRAINING SHOWERS/THUNDERSTORMS COULD SUPPORT LOCALLY EXCESSIVE
RAINFALL SUNDAY.

EVEN AS THE UPPER TROUGH PULLS AWAY SUNDAY NIGHT INTO MONDAY AND AN
UPPER RIDGE BUILDS INTO THE REGION FROM THE SOUTH/SOUTHEAST MONDAY
THROUGH TUESDAY...A NORTH/NORTHEAST TO SOUTH/SOUTHWEST BAND OF DEEP
MOISTURE WILL BE LEFT BEHIND OVER THE REGION...ESPECIALLY OVER
COASTAL COUNTIES. THUS...POPS ARE GRADUATED FROM SLIGHT
CHANCE/CHANCE INLAND TO HIGH CHANCE AT THE COAST THROUGH THIS
PERIOD. HIGHER POPS COULD OCCASIONALLY BE REQUIRED WITHIN COASTAL
COUNTIES. ALSO OF NOTE...HIGH PWATS AND WEAKENING LOW/MID LEVEL
WINDS COULD PROMOTE ERRATIC SHOWER/THUNDERSTORM PROPAGATION AND
LOCALLY EXCESSIVE RAINFALL.

WHILE FORECAST HIGH TEMPERATURES THROUGH THE PERIOD REMAIN IN THE
MID/UPPER 80S...SOME LOCATIONS WHERE SHOWERS ARE ONGOING TO START
THE DAY AND/OR WHERE CLOUDS/PRECIPITATION PERSIST FOR AN EXTENDED
PERIOD OF TIME...TEMPERATURES COULD STRUGGLE TO EXCEED THE LOWER
80S. LOW TEMPERATURES EACH NIGHT WILL RANGE FROM THE UPPER 60S/LOWER
70S INLAND TO THE MID/UPPER 70S NEAR THE COAST. STRATUS/FOG COULD
DEVELOP AT ANY TIME DURING THE LATE NIGHT/EARLY MORNING
HOURS...ESPECIALLY WHERE HEAVIEST RAIN OCCURS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
THROUGH THIS PERIOD...FORECAST DETAILS INCLUDING POPS WILL
SIGNIFICANTLY DEPEND ON THE STRENGTH AND TRACK OF THE REMNANTS OF
ERIKA...WHICH COULD DRIFT NORTH/NORTHEAST INTO THE REGION OR MEANDER
OVER THE SOUTHEAST. A STRONGER SYSTEM DRIFTING NORTH/NORTHEAST INTO
THE REGION COULD PRODUCE LOCALLY EXCESSIVE RAINFALL AND EVEN AN
INCREASED RISK FOR SEVERE WEATHER INCLUDING ISOLATED TORNADOES FOR
AT LEAST SOME PART OF THE LONG TERM PERIOD...WHILE A WEAKER SYSTEM
COULD MEANDER OUTSIDE OF OUR AREA WITH FEW DIRECT IMPACTS. FOR
NOW...THE FORECAST MAINTAINS HIGHER THAN NORMAL POPS...ESPECIALLY
DURING THE DAYTIME HOURS WHEN CHANCE TO HIGH CHANCE POPS ARE
INDICATED. TEMPERATURES SHOULD REMAIN CLOSE TO NORMAL...AND 90F
TEMPS ARE NOT INDICATED ANY DAY DURING THIS PERIOD. ASIDE FROM
INCREASING CONFIDENCE THAT THE REGION WILL NOT BE DIRECTLY IMPACTED
BY A SIGNIFICANT TROPICAL CYCLONE...UNCERTAINTY REMAINS HIGH
REGARDING IMPORTANT FORECAST DETAILS. EXPECT ADJUSTMENTS WITHIN
SUBSEQUENT FORECAST PACKAGES.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
KSAV...MAINTAINED VCSH TODAY WITH AS DEEP MOISTURE IN PLACE AND
HAVE NOW INCLUDED THERE A PREVAILING PERIOD OF SHOWERS FROM
MIDDAY INTO LATE AFTERNOON. CONTINUED CHANCES FOR SHOWERS THROUGH
TONIGHT BUT TIMING/COVERAGE SUGGEST VCSH PROBABLY THE BEST WAY TO
GO FOR NOW. MVFR CIGS ARE POSSIBLE THIS MORNING AND AGAIN TONIGHT
ESPECIALLY IN SHOWER AREAS.

KCHS...THE BULK OF CONVECTION WILL REMAIN SOUTH AND EAST OF THE
AIRFIELD THROUGH THIS EVENING...THUS NOTHING MORE THAN VFR
CEILINGS TO PREVAIL. WHILE SHOWER CHANCES DO INCREASE AFTER
MIDNIGHT TONIGHT...WE HAVE STARTED A TREND WITH AN INTRODUCTION TO
VCSH.

EXTENDED AVIATION OUTLOOK THROUGH THU...SATURDAY NIGHT INTO EARLY
NEXT WEEK...FLIGHT RESTRICTIONS COULD OCCUR WITH
SHOWERS/THUNDERSTORMS AND IN LATE NIGHT/EARLY MORNING STRATUS/LIGHT
FOG. OTHERWISE...MAINLY VFR. TUESDAY AND BEYOND...CONDITIONS REMAIN
HIGHLY DEPENDENT ON THE UNCERTAIN TRACK AND INTENSITY OF TROPICAL
CYCLONE ERIKA.

&&

.MARINE...
TODAY...THE COASTAL WATERS WILL BE SITUATED BETWEEN A WEDGE OF
HIGH PRESSURE INLAND AND THE REMNANTS OF A STATIONARY FRONT TO THE
S AND SE...PRODUCING NE AND E WINDS AT GENERALLY 15 KT OR LESS. A
MIX OF SWELLS AND WIND DRIVEN WAVES WILL COMBINE FOR SIGNIFICANT
WAVE HEIGHTS OF 2-4 FT WITH 3-5 FT SEAS BEYOND 20 NM...ESPECIALLY
EAST OF THE CHARLESTON PILOT BUOY.

A WEAK WARM FRONT COULD LIFT INTO THE GEORGIA WATERS OVERNIGHT BUT
THIS FEATURE SHOULD BEGIN TO BREAK DOWN LATE. CONDITIONS SHOULD
REMAIN BELOW SMALL CRAFT ADVISORY TONIGHT WITH SOMEWHAT WEAKER
FLOW THAN WHAT IS ONGOING EARLY TODAY.

SUNDAY THROUGH THURSDAY...OFFSHORE HIGH PRESSURE WILL MAINTAIN
ONSHORE WINDS CAPPED AT 15-20 KT...HIGHEST BEYOND NEARSHORE
WATERS...ACCOMPANIED BY SEAS 2-4 FT WITHIN NEARSHORE WATERS AND AS
HIGH AS 4-5 FT BEYOND 20 NM. MID TO LATE WEEK...ASSUMING THE
WEAKENING REMNANTS OF ERIKA REMAIN INLAND...A SLACKENING GRADIENT
COULD TRANSLATE TO WEAKENING ONSHORE WINDS AND SEAS SUBSIDING TO 1-3
FT.

RIP CURRENTS...WE HAVE MAINTAINED A MODERATE RISK OF RIP CURRENTS
AT AREA BEACHES TODAY GIVEN MODERATE ONSHORE WINDS...SMALL SWELLS
AND STRONG ASTRONOMICAL INFLUENCES DUE TO THE ELEVATED PERIGEAN
SPRING TIDES. IF WAVE PERIODS DO LENGTHEN JUST A BIT MORE...THE
RISK COULD BECOME HIGHER AT TYBEE TODAY. A PERSISTENT LONG PERIOD
SWELL...ONSHORE WINDS AND ASTRONOMICAL INFLUENCES WILL SUPPORT AN
ELEVATED RISK OF RIP CURRENTS INTO AT LEAST EARLY NEXT WEEK.

&&

.TIDES/COASTAL FLOODING...
THROUGH TONIGHT...ASTRONOMICAL INFLUENCES DUE TO THE PERIGEAN
SPRING TIDES PLUS ONSHORE WINDS WILL MAINTAIN ELEVATED HIGH TIDE
LEVELS ALONG THE COAST. WHILE WE WILL BE CLOSE TO POSSIBLE
SHALLOW COASTAL FLOODING IN CHARLESTON HARBOR WITH THIS MORNINGS
HIGH TIDE...A BETTER CHANCE FOR COASTAL FLOODING EXISTS WITH THE
EVENING HIGH TIDE. COASTAL FLOOD ADVISORIES WILL LIKELY BE
REQUIRED FOR AT LEAST PARTS OF THE SC COAST...AND WE/LL BE CLOSE
TO THE ADVISORY CRITERIA FURTHER SOUTH...INCLUDING THE FORT
PULASKI AREA.

SUNDAY THROUGH MONDAY...ASTRONOMICAL INFLUENCES DUE TO THE PERIGEAN
SPRING TIDE PLUS ONSHORE WINDS WILL MAINTAIN ELEVATED HIGH TIDE
LEVELS AT AND NEAR THE COAST. WHILE WE WILL BE CLOSE TO POSSIBLE
SHALLOW COASTAL FLOODING IN CHARLESTON HARBOR WITH THE MORNING HIGH
TIDES INTO EARLY NEXT WEEK...A BETTER CHANCE FOR SHALLOW SALT WATER
FLOODING EXISTS WITH THE EVENING HIGH TIDE SUNDAY AND MONDAY.
COASTAL FLOOD ADVISORIES WILL LIKELY BE REQUIRED FOR AT LEAST PARTS
OF THE SC COAST...AND WE/LL BE CLOSE TO THE ADVISORY CRITERIA
FURTHER SOUTH...INCLUDING THE SAVANNAH AREA. ALSO OF NOTE...PERIODS
OF SHOWERS/THUNDERSTORMS WITH HEAVY RAIN ARE EXPECTED THROUGH THE
PERIOD. IF HEAVY RAIN FALLS IN COASTAL COMMUNITIES...INCLUDING
DOWNTOWN CHARLESTON...AROUND THE TIMES OF HIGH TIDE MORE SIGNIFICANT
FLOODING IS POSSIBLE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

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


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