Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 171803
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
203 PM EDT THU APR 17 2014

.SYNOPSIS...
HIGH PRESSURE CENTERED WELL NORTH OF THE REGION WILL PERSIST THROUGH
TONIGHT...ALTHOUGH WILL BE SLOWLY WEAKENING WITH TIME. AN AREA OF
LOW PRESSURE WILL DEVELOP OVER THE NORTHEAST GULF OF MEXICO ON
FRIDAY. THIS LOW WILL THEN SLOWLY CROSS FLORIDA AND EVENTUALLY
MOVE OFF THE SOUTHEAST COAST BY THE LATTER PART OF THE WEEKEND.
HIGH PRESSURE WILL BUILD BACK IN EARLY NEXT WEEK. A WEAK COLD
FRONT MAY APPROACH THE AREA FROM THE NORTH BY MID WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY...NO MAJOR CHANGES. SKIES HAVE CLEARED ACROSS MOST OF
SOUTHEAST SOUTH CAROLINA BUT REMAIN RATHER CLOUDY ACROSS SOUTHEAST
GEORGIA...WHICH SHOULD BE THE TREND THE REST OF THE AFTERNOON.
TEMPS SHOULD TOP OUT IN THE UPPER 60S AWAY FROM THE LOCALLY COOLER
IMMEDIATE COASTAL LOCALES...ALTHOUGH SOME SPOTS COULD TOUCH 70. IT
WILL ALSO BE BREEZY AT TIMES WITH SOME GUSTS NEAR 25 MPH...MAINLY
NEAR THE COAST.

TONIGHT...HIGH CLOUDS WILL THICKEN OVERNIGHT AHEAD OF A
DEVELOPING GULF COAST SYSTEM. INCREASING DYNAMICS AND MOISTURE
CONVERGENCE TO OUR SW WILL SPREAD RAINS INTO THE FLORIDA PANHANDLE
AND SW GEORGIA AFTER MIDNIGHT. THE RISK FOR WET WEATHER IS
EXPECTED TO HOLD OFF UNTIL TOWARD DAYBREAK ACROSS THE SOUTHERN
HALF OF THE FORECAST AREA. CLOUDS AND LINGERING NE WINDS SHOULD
KEEP TEMPS MILDER OVERNIGHT...RANGING FROM THE MID TO UPPER 40S NW
TIER TO LOWER/MID 50S ALONG THE COAST.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
FRIDAY THROUGH SATURDAY...CONFIDENCE HAS INCREASED SIGNIFICANTLY IN
AN ACTIVE AND VERY WET SCENARIO FOR THE FORECAST AREA. OTHER THAN
THE NAM...THE LATEST RUNS OF THE SUITE OF FORECAST MODELS HAVE
CONVERGED ON A SOLUTION THAT FAVORS A WIDESPREAD SIGNIFICANT
RAINFALL EVENT STRETCHING FROM THE FLORIDA PANHANDLE AND UP THE
GEORGIA/SOUTH CAROLINA COASTLINE. ON FRIDAY...A SOUTHERN STREAM
SHORTWAVE WILL CROSS THE LOWER MISSISSIPPI VALLEY AND INTENSIFY INTO
A CLOSED LOW ACROSS THE DEEP SOUTH. AN IMPRESSIVE DEGREE OF FORCING
WILL TAKE SHAPE WITH RIGHT ENTRANCE REGION UPPER JET
DYNAMICS...STRONG LOW/MID LEVEL FRONTOGENESIS...AND DEEP MOIST
CONVERGENCE ALL ALIGNING ACROSS THE REGION ESPECIALLY FRIDAY NIGHT.
FURTHERMORE...PWATS WILL SURGE TO IN EXCESS OF 1.75 INCHES WHICH
WOULD EXCEED THE 99TH PERCENTILE FOR MID APRIL. PRECIPITATION WILL
INVADE FROM THE SOUTH ON FRIDAY...BECOMING MOST WIDESPREAD FRIDAY
NIGHT. POPS HAVE BEEN ALTERED DRAMATICALLY AND NOW FEATURE NEAR 100
PERCENT CHANCES BY LATE FRIDAY NIGHT. GIVEN THE PRESENCE OF THE
STRONG FORCING AND VERY MOIST AIRMASS...WIDESPREAD MODERATE TO
OCCASIONALLY HEAVY RAIN WILL OCCUR JUST ABOUT EVERYWHERE. BY
SATURDAY MORNING...SOME MODEL SOLUTIONS INDICATE A HIGH PROBABILITY
OF WIDESPREAD RAINFALL AMOUNTS OF 3 OR MORE INCHES. POPS THEN
DECREASE FROM WEST TO EAST DURING THE DAY ON SATURDAY AS THE FORCING
SHIFTS OFFSHORE AND THE SLOW MOVING SURFACE LOW DRIFTS OFF THE
FLORIDA COASTLINE. OF LESSER IMPACT...THE MODELS INDICATE THE
PRESENCE OF A SLOT OF STEEPENING MID LEVEL LAPSE RATES AND NEGATIVE
SHOWALTER INDICES FRIDAY NIGHT. THIS MAY RESULT IN SOME ELEVATED
THUNDERSTORM ACTIVITY...BUT FOR NOW THE HIGHEST PROBABILITIES ARE
OVER THE ADJACENT COASTAL WATERS. THUNDER MAY EVENTUALLY NEED TO BE
ADDED TO INLAND AREAS. THE FORECAST AREA HAS BEEN ADDED TO THE DAY 2
EXCESSIVE RAINFALL OUTLOOK FROM WPC...BUT CURRENT THINKING IS THAT
WIDESPREAD FLASH FLOODING IS NOT EXPECTED SO NOTHING WILL BE ADDED
TO THE HWO. THIS THREAT WILL NEED TO BE REEVALUATED WITH FUTURE
FORECAST PACKAGES. TEMPERATURES WILL BE HELD DOWN BY THE WIDESPREAD
CLOUDS AND PRECIPITATION SO FRIDAY HIGHS WILL BE KEPT IN THE LOW
60S...AND SATURDAY HIGHS IN THE MID/UPPER 60S.

SUNDAY...CONDITIONS WILL INCREASE AS THE COLUMN DRIES OUT AND THE
SURFACE LOW MOVES FURTHER OFFSHORE. IN FACT LAND AREAS ARE EXPECTED
TO BE DRY WITH JUST LOW END CHANCES OVER THE COASTAL WATERS. WE MAY
HAVE TO DEAL WITH CONSIDERABLE WRAP AROUND CLOUDINESS WHICH MAY
NEGATIVELY IMPACT TEMPERATURES. FOR NOW...THE FORECAST FEATURES LOW
70S JUST ABOUT EVERYWHERE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
OVERALL THE LONG TERM PERIOD LOOKS QUIET FOR THE FORECAST AREA.
RIDGING ALOFT WILL MOVE IN FOR EARLY IN THE WEEK BEHIND THE
DEPARTING UPPER LOW. A WEAK TROUGH MAY MOVE THROUGH BY THE MID WEEK
TIME PERIOD. WEAK HIGH PRESSURE WILL SETTLE OVER THE REGION THROUGH
TUESDAY...WITH A WEAK COLD FRONT ATTEMPTING TO CROSS BY WEDNESDAY.
THERE MAY BE A FEW SHOWERS WITH THE FRONT...BUT POPS HAVE BEEN
LIMITED TO THE SLIGHT CHANCE RANGE. TEMPERATURES FEATURE A WARMING
TREND...REACHING AROUND THE 80 DEGREE MARK BY TUESDAY AND CONTINUING
THROUGH THE END OF THE FORECAST PERIOD.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR THROUGH AT LEAST 06Z...THEN MVFR/POSSIBLY IFR CIGS. SHOWERS TO
MOVE IN FROM THE SOUTH...LIKELY IMPACTING KSAV INITIALLY. THE RAIN
COULD BE MODERATE TO HEAVY AT TIMES WHICH COULD REDUCE VSBY AS
WELL. NE WINDS WILL BE GUSTY AT TIMES ...LIKELY THE STRONGEST
AFTER DAYBREAK FRI AS THE PRESSURE GRADIENT TIGHTENS MORE AS LOW
PRESSURE BEGINS TO APPROACH FROM THE SOUTHWEST.

EXTENDED AVIATION OUTLOOK...CHANCES OF SUB-VFR CONDITIONS ARE
INCREASING...ESPECIALLY BEGINNING FRIDAY NIGHT. THESE CONDITIONS
WILL LIKELY PERSIST THROUGH SATURDAY...IMPROVING SUNDAY AND INTO
EARLY NEXT WEEK.

&&

.MARINE...
SOLID SMALL CRAFT ADVISORY CONDITIONS EXPECTED THROUGH TONIGHT AS
THE PRES GRADIENT REMAINS TIGHT BETWEEN HIGH PRES WEDGED DOWN THE
LEE OF THE MOUNTAINS AND DEVELOPING LOW PRES BY TONIGHT OVER
THE NE GULF OF MEXICO. MODELS SUGGEST THE ONGOING SURGE IN THE
20-25 KT WITH GUSTS TO 30 KT MAY EBB ALONG THE CHARLESTON COUNTY
COAST LATER TODAY AND THIS EVENING TO MORE OF A 15-20 KT FLOW
BUT THEN SURGE AGAIN AFTER MIDNIGHT FRIDAY MORNING. OVER GEORGIA
WATERS...NOT MUCH OF A LULL WITH THE STEADY NE FLOW THROUGH
TONIGHT WITH POTENTIAL FOR PINCHING TO PERSIST RIGHT ALONG COASTAL
BEAUFORT AND CHATHAM COUNTIES GIVEN THE ALIGNMENT OF THE ENHANCED
MOISTURE GRADIENTS. SEAS WILL REMAIN IN THE 5-8 FT RANGE WITHIN
20 NM AND UP TO 10 FT OFFSHORE CLOSER TO THE GULF STREAM INTO
TONIGHT.

FRIDAY THROUGH MONDAY...A STRONG NORTHEAST GRADIENT WILL PERSIST
THROUGH FRIDAY BETWEEN HIGH PRESSURE TO THE NORTH AND DEVELOPING LOW
PRESSURE TO THE SOUTH. FORECAST UNCERTAINTY THEN INCREASES FRIDAY
NIGHT ONWARD AS THE SURFACE LOW BEGINS TO MOVE OUT OF THE NORTHEAST
GULF OF MEXICO AND ACROSS FLORIDA. LATEST MODEL GUIDANCE HAS
FLUCTUATED TO FAVORING A SURFACE LOW TRACK CLOSER TO THE COAST AND
TO THE LOCAL WATERS. IF THIS OCCURS...THE GRADIENT MAY ACTUALLY
RELAX AND RESULT IN WEAKER FLOW. HOWEVER...IF THE LOW REMAINS
FURTHER TO THE SOUTH...THE GRADIENT MAY ACTUALLY BE ENHANCED AND
RESULT IN THE POSSIBILITY OF GALE EVENT AND HIGH SURF FRIDAY NIGHT
THROUGH SATURDAY. FORECAST CONFIDENCE IS TOO LOW TO SAY WHICH
SCENARIO IS MORE LIKELY AT THIS POINT. THEREFORE...THE CURRENT SMALL
CRAFT ADVISORIES HAVE BEEN LEFT INTACT...AND SUBSEQUENT FORECAST
UPDATES WILL HAVE TO READDRESS THE POTENTIAL FOR THESE HAZARDS.
THERE IS BETTER CERTAINTY FOR THE LATE WEEKEND AND EARLY WEEK TIME
PERIOD WHEN THE LOW IS EXPECTED TO BE FAR ENOUGH EAST FOR ANOTHER
ROUND OF ENHANCED GRADIENT ACROSS THE WATERS. STRONG WINDS AND
ELEVATED SEAS APPEAR LIKELY SUNDAY INTO MONDAY.

RIP CURRENTS...A BIT OF AN UNDERLYING LONGER PERIOD SWELL NOTED FROM
FRYING PAN SHOALS TO GRAYS REEF OVERNIGHT WAS ENOUGH TO TIP OUR
MODERATE RISK TO A HIGH RISK FROM BEAUFORT COUNTY SOUTHWARD. A
MODERATE RISK FOR RIP CURRENTS CONTINUES FOR CHARLESTON BEACHES
TODAY WITH AN ENHANCED LONGSHORE CURRENT. AN ENHANCED RISK FOR RIP
CURRENTS WILL PERSIST THROUGH THE WEEKEND AND PERHAPS INTO EARLY
NEXT WEEK.

&&

.HYDROLOGY...
THE PROBABILITY OF A WIDESPREAD SIGNIFICANT RAINFALL EVENT IS
INCREASING FOR SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA. THE
HEAVIEST RAIN IS EXPECTED TO OCCUR FRIDAY NIGHT THROUGH SATURDAY
MORNING. MODERATE TO OCCASIONALLY HEAVY RAIN IS LIKELY...AND TOTAL
RAINFALL AMOUNTS WILL GENERALLY RANGE FROM 1-3 INCHES. THE HIGHEST
AMOUNTS WILL OCCUR ALONG AND NEAR THE COAST...WITH SOME LOCALLY
GREATER TOTALS POSSIBLE. THIS RAINFALL MAY CAUSE FLOODING ISSUES
AROUND THE TIMES OF HIGH TIDE ALONG THE COAST INCLUDING DOWNTOWN
CHARLESTON AND SAVANNAH...AS WELL AS PONDING OF WATER ELSEWHERE
ESPECIALLY IN LOW LYING AND POOR DRAINAGE AREAS. ALSO...MAIN STEM
RIVERS AND ASSOCIATED TRIBUTARIES WILL LIKELY SEE RISES WITH THE
POTENTIAL FOR MINOR FLOODING DEPENDING ON OBSERVED RAINFALL AMOUNTS.

&&

.TIDES/COASTAL FLOODING...
TIDES WILL CONTINUE TO RUN HIGH THROUGH THE WEEKEND AND COASTAL
FLOOD ADVISORIES COULD BE NEEDED DURING THE NIGHTTIME HIGH TIDE
CYCLES.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HIGH RISK FOR RIP CURRENTS UNTIL 8 PM EDT THIS EVENING FOR
     GAZ117-119-139-141.
SC...HIGH RISK FOR RIP CURRENTS UNTIL 8 PM EDT THIS EVENING FOR
     SCZ048-051.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT SUNDAY FOR AMZ350-352-354.
     SMALL CRAFT ADVISORY UNTIL 2 PM EDT MONDAY FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR AMZ330.

&&

$$

SYNOPSIS...
NEAR TERM...RJB
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...RJB
MARINE...BSH/RJB
HYDROLOGY...
TIDES/COASTAL FLOODING...






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