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Area Forecast Discussion

295
FXUS62 KCHS 290539
AFDCHS

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

.SYNOPSIS...
THE REMNANTS OF A STATIONARY FRONT WILL SLOWLY DISSIPATE EAST AND SE
OF THE AREA THROUGH SATURDAY...AS A WEAK INLAND WEDGE REMAINS IN
PLACE. ATLANTIC HIGH PRESSURE WILL THEN EXPAND ACROSS THE REGION
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 AM THIS MORNING/...
NOT MUCH CHANGE FOR THE REMAINDER OF THE NIGHT. A WEAK SHORT WAVE
WAS LIFTING NORTH ACROSS THE FORECAST AREA RESULTING IN THICKER
CLOUD COVER ACROSS SE GEORGIA WITH AREAS OF LAYERED CLOUDS ACROSS
SE SOUTH CAROLINA. THE BETTER CHANCES FOR SHOWERS OVERNIGHT WILL
BE ACROSS COASTAL SOUTHEAST GEORGIA AND SOUTH OF EDISTO BEACH SC.
GOOD LOW LEVEL MOISTURE CONVERGENCE SHOULD RESULT IN MAINLY LOW-
TOPPED CONVECTIVE RAINS. LOCALIZED DOWNPOURS ARE POSSIBLE ALONG
THE BEACHES AND BARRIER ISLANDS.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/...
SATURDAY THROUGH SATURDAY NIGHT...A MID/UPPER LOW IN THE NORTHERN
GULF OF MEXICO WILL REMAIN IN PLACE FOR THE START OF THE
WEEKEND...EVENTUALLY WEAKENING AND STARTING TO OPEN UP AS IT LIFTS
NORTH/NE BY SUNDAY. THIS FEATURE WILL BE STEERED WEST/SW OF THE
LOCAL REGION BY A FORMIDABLE SUB-TROPICAL LOW AND MID-LEVEL RIDGE
CENTERED IN THE SW ATLANTIC ALONG ROUGH 30N. AT THE SURFACE WE FIND
THE THE REMAINS OF A STATIONARY FRONT OFF TO THE EAST/SE THAT WILL
CONTINUE TO DISSIPATE...WHILE A WEDGE OF HIGH PRESSURE INLAND SLOWLY
WEAKENS THROUGH THE PERIOD. WHILE THERE IS DECENT CAPPING AND LESS
MOISTURE OVER FAR NORTHERN ZONES...THERE IS A GOOD INFLUX OF SUB-
TROPICAL AIR ARRIVING WITHIN A DEEP SOUTH/SW FLOW FROM THE GULF.
PWATS WILL SURGE TO 2-2.25 INCHES OVER SOUTHERN ZONES...APPROACHING
2 INCHES CENTRAL AREAS...BUT LIMITED TO 1.5 TO 1.75 INCHES NORTH. AS
A RESULT WE ANTICIPATE A SHARP NORTH-SOUTH GRADIENT IN REGARDS TO
CONVECTIVE RAINS. ALTHOUGH ADJUSTMENTS WILL BE REQUIRED ONCE TRENDS
BECOME APPARENT...WE HAVE SHOWN 60 POPS SOUTH...30-50 POPS CENTRAL
SECTIONS AND 20 POPS NORTH. A SLUGGISH STORM MOTION AND THE
ABUNDANCE OF MOISTURE WILL LEAD TO LOCALLY HEAVY RAINFALL...ALTHOUGH
SHOULD THE HEAVIER RAINS OCCUR NEAR HIGH TIDE THE FLOODING RISK
COULD BE WORSE. COVERAGE OF CONVECTION WILL WANE OVER MOST LAND
BASED COUNTIES DURING THE EVENING HOURS...BEFORE THE BEST
FORCING/MOISTURE CONVERGENCE OCCURS OVER THE ATLANTIC AND ON THE
COASTAL COUNTIES OVERNIGHT. TEMPS WILL BE HELD TO THE MID OR UPPER
80S SATURDAY...THEN DROP TO THE LOWER AND MID 70S AT NIGHT.

SUNDAY THROUGH MONDAY...THE GULF COAST LOW ALOFT WILL HAVE OPENED
INTO A WAVE AND CONTINUES TO HEAD NE NEAR THE SPINE OF THE
APPALACHIANS...ALLOWING FOR A DEEP-LAYERED SUB-TROPICAL RIDGE TO
EXPAND WEST ACROSS THE LOCAL DISTRICT. THIS PATTERN ALSO LOOKS TO
STEER ERIKA ON A MORE WEST/NW TRACK INTO PERHAPS THE GULF OF MEXICO.
EVEN SO A CONSIDERABLE AMOUNT OF SUB-TROPICAL MOISTURE WILL
CONTINUE TO FEED INTO THE SE FROM BOTH THE ATLANTIC AND GULF OF
MEXICO AS PWATS ARE SOME 2 STANDARD DEVIATIONS ABOVE NORMAL FOR LATE
AUGUST. SUBTLE MID LEVEL PERTURBATIONS WILL STREAM OVERHEAD WITHIN
THE SOUTH/SW FLOW ALOFT...AND COMBINED WITH THE RICH MOISTURE WILL
LEAD TO AT LEAST CHANCE TO LIKELY DAYTIME POPS AND SLIGHT
CHANCE/CHANCE NIGHTTIME POPS. LIMITED STORM MOTION WILL AGAIN CAUSE
THE POTENTIAL FOR LOCALLY HEAVY RAINS...CAUSING A MORE SIGNIFICANT
FLOODING RISK SHOULD THE HEAVY RAINS OCCUR NEAR THE TIMES OF HIGH
TIDE. EXTENSIVE CLOUD COVER AND THE WET ATMOSPHERE WILL HOLD DAYTIME
HIGHS BELOW NORMAL...WHILE TEMPS AVERAGE NEAR OR SLIGHTLY ABOVE
CLIMO AT NIGHT.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
MANY FORECAST DETAILS DEPEND ON THE HIGHLY UNCERTAIN TRACK AND
STRENGTH OF TROPICAL STORM ERIKA NEXT WEEK. RECENT FORECASTS DEPICT
THE SYSTEM NOW HEADING INTO THE GULF OF MEXICO...THEN PERHAPS COMING
ASHORE ALONG THE NORTHEAST GULF COAST. THE LATEST LOCAL 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.
HOWEVER...THERE REMAINS SEVERAL DIFFERENT POSSIBLE SCENARIOS OF
ERIKA...PENDING WHETHER OR NOT THE SYSTEM SHIFTS INTO THE
GULF...MOVES INTO FLORIDA...STAYS EAST OF THE FLORIDA PENINSULA OR
EVEN FALLS APART COMPLETELY. SO LARGE UNCERTAINTIES STILL REMAIN IN
PLACE...ALTHOUGH A MORE WESTERN TRACK LEADS TO LESS IMPACTS THAN A
MORE EASTWARD TRACK. IN SPITE OF THE SHIFT IN TRACK...ALL SHOULD
CONTINUE TO CLOSELY MONITOR THE PROGRESS OF THE SYSTEM...STAYING
TUNED TO THE LATEST FORECASTS FROM THE NATIONAL HURRICANE CENTER AND
OUR OFFICE CONCERNING ERIKA.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
KSAV...MAINTAINED VCSH OVERNIGHT AS DEEP MOISTURE IN PLACE AND
LOW LEVEL SPEED CONVERGENCE ALONG THE ATLC LAND/SEA INTERFACE.
THERE ARE SMALL CHANCE FOR MVFR CIGS LATER TONIGHT. INCREASING
CHANCE FOR SHOWERS AND MVFR CIGS ON SATURDAY. WE LOWERED CIGS
TO BKN035 TO TREND GIVEN SOME UNCERTAINTY IN TIMING SHOWERS IN.

KCHS...THE BULK OF CONVECTION WILL REMAIN SOUTH AND EAST OF THE
AIRFIELD TONIGHT AND SATURDAY...THUS NOTHING MORE THAN VFR
CEILINGS TO PREVAIL. STILL...THERE IS A LOW END RISK FOR
OCCASIONAL FLIGHT RESTRICTIONS IN LOW CLOUDS LATE TONIGHT/EARLY
SATURDAY AND IN ISOLATED SHRA THIS AFTERNOON.

EXTENDED AVIATION OUTLOOK...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...
OVERNIGHT...A TIGHT SURFACE PRESSURE GRADIENT AND AN UNSTABLE
MARINE BOUNDARY LAYER WILL SUPPORT E/NE WINDS AROUND 15-20 KNOTS.
BY DAYBREAK...WINDS SHOULD BEGIN TO DIMINISH AS THE GRADIENT
RELAXES/ . SEAS WILL BE MAINLY 2-4 FT WITHIN NEARSHORE WATERS AND
4-5 FT BEYOND 20 NM. WE LOWERED WINDS A BIT IN THE CHARLESTON
HARBOR GIVEN LATEST OBS/TRENDS. BETTER CHANCES FOR GUSTY WINDS
OUTSIDE THE JETTIES.

SATURDAY...THE COASTAL WATERS WILL BE SITUATED BETWEEN
A WEDGE OF HIGH PRESSURE INLAND AND THE REMNANTS OF A STATIONARY
FRONT TO THE EAST/SE...PRODUCING NE/EAST 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.

SATURDAY NIGHT THROUGH SUNDAY NIGHT...SUB-TROPICAL ATLANTIC HIGH
PRESSURE WILL GRADUALLY BUILD OVER THE WATERS...WHICH SHOULD SHUNT
ERIKA FURTHER SOUTH/SW THEN ORIGINALLY ANTICIPATED. THIS WILL RESULT
IN GENERALLY EASTERLY WINDS OF 15 KT OR LESS...AND SEAS WILL AGAIN
BE A MIXTURE OF LONG PERIOD SWELLS AND SHORTER PERIOD WIND DRIVEN
WAVES...AS THESE COMBINED SEAS HOLD AT OR BELOW 4 OR 5 FT.

MONDAY NIGHT THROUGH MIDWEEK...WINDS/SEAS WILL DEPEND ON THE
UNCERTAIN TRACK AND INTENSITY OF TROPICAL STORM ERIKA. PLEASE STAY
TUNED TO THE LATEST FORECASTS FROM THE NATIONAL HURRICANE CENTER AND
OUR OFFICE CONCERNING ERIKA.

RIP CURRENTS...WE HAVE RAISED A MODERATE RISK OF RIP CURRENTS AT
AREA BEACHES FOR SATURDAY GIVEN MODERATE ONSHORE WINDS...SMALL
SWELLS AND STRONG ASTRONOMICAL INFLUENCES DUE TO THE ELEVATED
PERIGEAN SPRING TIDES.

A PERSISTENT LONG PERIOD SWELL...ONSHORE WINDS AND ASTRONOMICAL
INFLUENCES WILL SUPPORT AN ELEVATED RISK OF RIP CURRENTS INTO AT
LEAST EARLY NEXT WEEK...PERHAPS EVEN LONGER PENDING THE FUTURE
EVOLUTION AND TRACK OF ERIKA.

&&

.TIDES/COASTAL FLOODING...
SATURDAY THROUGH MONDAY...ASTRONOMICAL INFLUENCES DUE TO THE
PERIGEAN SPRING TIDES 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
COASTAL FLOODING EXISTS WITH THE EVENING HIGH TIDE EACH DAY
THROUGH 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.

TUESDAY THROUGH WEDNESDAY/THURSDAY...ASTRONOMICAL INFLUENCES WILL
WANE. HOWEVER...ELEVATED TIDES COULD PERSIST THROUGH THE WEEK
PENDING WHAT BECOMES OF ERIKA. PLEASE STAY TUNED TO THE LATEST
FORECASTS FROM THE NATIONAL HURRICANE CENTER AND OUR OFFICE
CONCERNING ERIKA.

&&

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

&&

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



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