Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 070517
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
117 AM EDT THU MAY 7 2015

.SYNOPSIS...
LOW PRESSURE WILL SLOWLY LIFT NORTHWARD WELL OFF THE SOUTHEAST
COAST TODAY INTO FRIDAY...AND MAY BECOME NEARLY STATIONARY JUST
OFF THE SOUTH CAROLINA COAST FRIDAY INTO SATURDAY. THE LOW IS THEN
EXPECTED TO LIFT NORTH ACROSS THE NORTH CAROLINA OUTER BANKS INTO
MONDAY. A WEAK COLD FRONT MAY PUSH THROUGH THE REGION BY THE
MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
SURFACE/MARINE OBSERVATIONS AND SATELLITE DATA SUGGEST LOW
PRESSURE IS SLOWLY ORGANIZING WELL EAST OF THE FLORIDA/GEORGIA
BORDER. SHOWER/TSTM ACTIVITY REMAINS FAIRLY LIMITED SO FAR...BUT
COOLING CLOUD TOPS ARE EXPANDING/CONSOLIDATING ALONG THE FAR
NORTHERN FLANK OF THE BROAD CIRCULATION CENTER CLOSER TO THE GULF
STREAM. WATER VAPOR IMAGERY DOES SHOW DRY AIR ENTRAINING INTO THE
CIRCULATION FROM THE SOUTH AND SOUTHEAST...SO RAPID INTENSIFICATION
IS UNLIKELY. THE NATIONAL HURRICANE CENTER CONTINUES TO MONITOR
THIS SYSTEM FOR POSSIBLE TROPICAL OR SUBTROPICAL DEVELOPMENT
DURING THE NEXT 12-48 HOURS...BUT IT IS IMPORTANT TO NOTE THAT
IMPACTS WILL BE THE SAME WHETHER THE SYSTEM IS NAMED OR NOT.

EXPECT DRY CONDITIONS FOR MUCH OF THE AREA TONIGHT WITH MAINLY
CLEAR SKIES WITH ONE CAVEAT AREA. HIGH RESOLUTION MODELS AND
CURRENT RADAR TRENDS INDICATE LIGHT RAINS WILL SPREAD INTO FAR NE
CHARLESTON COUNTY AND WE RAISED POPS ALONG THE COAST NE OF
CHARLESTON BUT MAINLY BRUSHING THE COAST. BREEZY CONDITIONS WILL
PERSIST ALONG THE SOUTH CAROLINA BEACHES...ESPECIALLY THE BEACHES
OF CHARLESTON COUNTY...WHERE GUSTS OF 20-30 MPH.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/...
THE MAIN CONCERN FOR THE SHORT TERM FORECAST WILL DEAL WITH LOW
PRESSURE DEVELOPING OFF THE SOUTHEAST U.S. COAST AND ITS EVENTUAL
TRACK...INTENSITY...AND PROXIMITY TO THE COAST THURSDAY INTO
SATURDAY. AT THIS TIME...THE NATIONAL HURRICANE CENTER HAS
INDICATED A 60 PERCENT CHANCE OF CYCLONE FORMATION OFF THE
SOUTHEAST COAST THURSDAY OR FRIDAY.

THERE REMAINS SOME NOTABLE DIFFERENCES IN THE EXPECTED TRACK OF THE
LOW PRESSURE SYSTEM AS IT LIFTS NORTH OFF THE SOUTHEAST COAST AND
APPROACHES THE AREA THURSDAY. MOST OPERATIONAL GUIDANCE PICKS UP ON
A DEVELOPING LOW CIRCULATION TO THE NORTH OF THE BAHAMAS. AS A
RESULT...A MORE EASTWARD TRACK OF THE LOW IS INITIALLY SUGGESTED BY
THE LATEST 12Z NAM AND GFS MODELS AS WELL AS THE LATEST ECMWF.
HOWEVER...THE LATEST 12Z INVEST INITIATED THE MAIN LOW CIRCULATION
NORTHWEST OF THE BAHAMAS...WHICH EVENTUALLY CLUSTERS THE TRACK OF
THE LOW MUCH CLOSER TO THE SOUTH CAROLINA COAST. REGARDLESS OF WHERE
THE DOMINANT CIRCULATION DEVELOPS...THE BIGGEST FACTOR IN THE TRACK
OF THE LOW PRESSURE SYSTEM WILL BE THE STRENGTH OF THE RIDGE OF HIGH
PRESSURE EXTENDED ACROSS THE ATLANTIC TO THE NORTH.

LATEST MODEL CONSENSUS IS THAT THE LOW WILL TRACK NORTHWARD WHILE
THE ATLANTIC RIDGE IS WEAKENED...GAIN TROPICAL/SUBTROPICAL
CHARACTERISTICS WHILE PASSING OVER WARMER GULF STREAM WATERS AND
ENCOUNTERING LESS DEEP LAYER SHEAR OFF THE SOUTHEAST COAST...THEN
MEANDER AROUND LATITUDE 32 NORTH BEFORE MAKING A WESTWARD TURN AS
THE RIDGE OF HIGH PRESSURE STRENGTHENS LATER THURSDAY AND FRIDAY.
THIS SCENARIO DOES PUT THE CENTER OF THE LOW CLOSER OFF THE
CHARLESTON COUNTY COAST THROUGH FRIDAY...WITH EVEN SOME MODELS
SUGGESTING A RETROGRADING LOW VERY CLOSE TO THE COAST INTO SATURDAY.
GIVEN THIS LATEST SCENARIO...THE MAIN IMPACTS FROM THE SYSTEM WILL
CONTINUE TO BE AN INCREASED RISK OF RIP CURRENTS...SHALLOW COASTAL
FLOODING....AND SOME BEACH EROSION. DESPITE BEING ON THE WESTERN
SIDE OF THE SYSTEM INITIALLY...A THREAT OF HEAVY RAINFALL WILL ALSO
BE POSSIBLE FOR MANY AREAS IN SOUTHEAST SOUTH CAROLINA AND PERHAPS
IN PARTS OF SOUTHEAST GEORGIA SHOULD THE LOW MAKE A MORE SIGNIFICANT
SHIFT WESTWARD AND MEANDER OVER THE AREA THROUGH MUCH OF THE
WEEKEND. HOWEVER...FORECAST CONFIDENCE REMAINS LOW IN HOW FAR NORTH
THE SYSTEM REACHES BEFORE MAKING A SHIFT WEST AND HOW FAR WEST THE
SYSTEM TRACKS THEREAFTER TO INDICATE A SIGNIFICANTLY HIGHER
POTENTIAL FOR HEAVY RAINFALL. AS A RESULT...ONLY SLIGHT INCREASES TO
THE OVERALL POP TREND HAS BEEN INDICATED IN THE LATEST FORECAST
PACKAGE FOR THIS WEEKEND.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
THE LOW IS EXPECTED TO LIFT NORTHWARD TOWARD EASTERN NORTH CAROLINA
SUNDAY AND SUNDAY NIGHT WITH A PREVAILING SOUTHWEST FLOW SETTING UP
FOR MONDAY AND TUESDAY AHEAD OF AN APPROACHING WEAK COLD FRONT. THE
FRONT MAY PUSH THROUGH THE AREA BY WEDNESDAY WITH HIGH PRESSURE
BUILDING IN FROM THE NORTH. THE OVERALL TREND FOR THE LONG TERM
PERIOD IS FOR WARMING AND WELL ABOVE NORMAL TEMPERATURES WITH HIGHS
IN THE MID/UPPER 80S AND LOWS IN THE UPPER 60S. WE MAY ALSO SEE
ISOLATED TO SCATTERED DIURNAL CONVECTION EACH AFTERNOON WITH THE
STRONG SURFACE HEATING TAKING PLACE.

&&

.AVIATION /05Z THURSDAY THROUGH MONDAY/...
KCHS...VFR THROUGH SUNRISE WITH INCREASING PROBABILITIES FOR AT
LEAST MVFR VSBYS/CIGS AND LIGHT RAINS AS DEEP MOISTURE INCREASES
OVER THE CENTRAL SOUTH CAROLINA COAST. GUSTY WINDS ARE LIKELY...
ESPECIALLY FROM SUNRISE. GIVEN LATEST MODEL DATA AND RADAR TRENDS
WE HAVE PREVAILED RAINS TODAY BUT THERE COULD BE A SHARP EDGE FOR
THE PCPN SHIELD. FURTHER REFINEMENTS WILL BE NEEDED AS DETAILS ON
THE OFFSHORE LOW BECOME MORE APPARENT.

KSAV...VFR. GUSTY N WINDS ARE LIKELY AFTER SUNRISE.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS ARE POSSIBLE
TONIGHT THROUGH SATURDAY...ESPECIALLY AT KCHS...BASED ON THE
EVENTUAL TRACK OF THE DEVELOPING LOW PRESSURE SYSTEM OFF THE
COAST. OTHERWISE VFR CONDITIONS ARE EXPECTED TO PREVAIL.

&&

.MARINE...
OVERNIGHT...A GALE WATCH FOR THE CHARLESTON COUNTY COASTAL WATERS
IS IN EFFECT WHERE HIGH RESOLUTION MODELS SUGGEST FREQUENT GUSTS
TO 35 KT COULD OCCUR TODAY AS THE PRESSURE GRADIENT ALONG THE LOW
OFFSHORE AND HIGH PRESSURE TO THE NORTH TIGHTENS. IN
ADDITION...BANDS OF SHOWERS WILL SUPPORT SQUALLY WEATHER WHICH
COULD PRODUCE LOCAL WIND GUSTS IN EXCESS OF 40 KT. IT IS VERY
POSSIBLE A GALE WARNING OR A TROPICAL STORM WARNING MAY BE
NEEDED...DEPENDING ON HOW THE SYSTEM EVOLVES OVER THE NEXT 12
HOURS OR SO.

THURSDAY NIGHT THROUGH SUNDAY...THE DETAILS OF THE FORECAST WILL
REMAIN HIGHLY DEPENDENT ON THE AREA OF LOW PRESSURE OFF THE COAST
AND ITS EVENTUAL TRACK AND INTENSITY. AS OF NOW...THE PREFERRED
TRACK IS FOR THE SYSTEM TO PASS JUST EAST OF THE LOCAL WATERS
INITIALLY AS IT SLOWLY LIFTS NORTHWARD INTO THE WEEKEND. THIS WILL
BRING A TIGHTENING PRESSURE GRADIENT INTO THE WATERS ON THURSDAY
THAT PERSISTS THROUGH AT LEAST EARLY FRIDAY. CURRENT MODEL TRENDS
DO NOT EXPLICITLY FAVOR THE POSSIBILITY FOR GALES...BUT CONFIDENCE
IS LOW GIVEN THE POSSIBILITY FOR THIS SYSTEM TO BECOME TROPICAL IN
NATURE. AT THE VERY LEAST...SOLID SMALL CRAFT ADVISORY CONDITIONS
ARE EXPECTED FOR ALL WATERS...AND POSSIBLY FOR THE CHARLESTON
HARBOR...WITH STRENGTHENING WINDS AND BUILDING SEAS. SMALL CRAFT
ADVISORIES WILL THEREFORE REMAIN IN EFFECT THROUGH LATE THURSDAY
NIGHT...BEFORE IMPROVING ENOUGH TO WHERE WE SEE CONDITIONS IMPROVE
TO BELOW ADVISORY LEVELS STARTING FROM SOUTHWEST TO NORTHEAST OVER
COASTAL WATERS INTO THE WEEKEND. THE WORST CONDITIONS ARE EXPECTED
OFF THE CHARLESTON COUNTY COAST WHICH WILL BE CLOSEST TO THE
CENTER OF THE LOW. STAY TUNED TO FORECAST UPDATES AS WELL AS
DETAILS FROM THE NATIONAL HURRICANE CENTER REGARDING THE TRACK AND
INTENSITY OF THIS LOW PRESSURE SYSTEM.

RIP CURRENTS...STRONG WINDS ALONG WITH INCREASING SWELL AND MULTIPLE
REPORTS OF RIP CURRENTS OBSERVED TODAY...WILL RESULT IN A HIGH RISK
OF RIP CURRENTS ON THURSDAY. AN ELEVATED RISK FOR RIP CURRENTS WILL
LIKELY CONTINUE ON FRIDAY AS AN AREA OF LOW PRESSURE SLOWS OFF THE
COAST. THE RISK MAY THEN BEGIN TO DIMINISH AS THE LOW LEVEL FLOW
TURNS MORE OFFSHORE AND NORTH AND NORTHWEST WITH TIME.

&&

.TIDES/COASTAL FLOODING...
INCREASING NORTH WINDS TONIGHT WILL RESULT IN ABOVE NORMAL TIDES
ALONG THE COAST...ALTHOUGH SHOULD NOT REACH ADVISORY LEVELS. TIDE
LEVELS WILL CONTINUE TO BE ELEVATED THE NEXT SEVERAL DAYS WITH LOW
PRESSURE OFFSHORE SO WILL CONTINUE TO MONITOR FOR POSSIBLE SHALLOW
COASTAL FLOODING...MAINLY DURING THE EVENING HIGH
TIDES...ESPECIALLY IF HEAVY RAINFALL OCCURS AROUND THE SAME TIME.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HIGH RISK FOR RIP CURRENTS FROM 8 AM EDT THIS MORNING THROUGH
     THIS EVENING FOR GAZ117-119-139-141.
SC...HIGH RISK FOR RIP CURRENTS FROM 8 AM EDT THIS MORNING THROUGH
     THIS EVENING FOR SCZ048>051.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT FRIDAY FOR AMZ352.
     GALE WATCH FROM 6 AM EDT THIS MORNING THROUGH THIS AFTERNOON
     FOR AMZ350.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR
     AMZ350.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR AMZ354.
     SMALL CRAFT ADVISORY UNTIL 8 PM EDT FRIDAY FOR AMZ374.

&&

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


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