Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 041407
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1007 AM EDT MON MAY 4 2015

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL PREVAIL TODAY INTO WEDNESDAY. AN AREA
OF LOW PRESSURE IS EXPECTED TO DEVELOP OFF THE EAST COAST OF
FLORIDA ON WEDNESDAY...AND LIFT NORTHWARD OFF THE SOUTHEAST COAST
THROUGH THURSDAY. THE LOW COULD THEN MEANDER BACK TOWARD THE COAST
THROUGH FRIDAY...AND LINGER NEARBY THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
SURFACE HIGH PRESSURE WILL REMAIN ANCHORED OVER THE MID ATLANTIC
TODAY. A FEW HI RESOLUTION MODELS HINT AT A FEW SHOWERS DEVELOPING
ALONG THE INLAND PENETRATING SEA BREEZE THIS AFTERNOON.
HOWEVER...MODEL SOUNDINGS INDICATE A STRONG SUBSIDENCE INVERSION
ALOFT AND WITH LIMITED MOISTURE HAVE OPTED TO KEEP A DRY FORECAST
IN PLACE. IF AN ISOLATED SHOWER DOES DEVELOP...IT WILL BE QUITE
BRIEF WITH VERY LITTLE QPF. OTHERWISE...A DECENT DIURNAL CU FIELD
EXPECTED. LOW LEVEL THICKNESS VALUES FROM KCHS 12Z RAOB SUPPORTS
HIGHS IN THE LOW 80S AWAY FROM THE LOCALLY COOLER COASTLINE.

WITH THIS UPDATE...MADE ADJUSTMENTS TO HOURLY T/TD GRIDS AS CURRENT
OBSERVATIONS WERE RUNNING A FEW DEGREES HIGHER.

EXPECT ANOTHER TRANQUIL NIGHT AS ATLANTIC HIGH PRESSURE RIDGES
ONSHORE ACROSS THE REGION. LOWS SHOULD RANGE FROM THE MID 50S
INLAND TO MID 60S ON THE COAST. PATCHY GROUND FOG COULD ONCE AGAIN
DEVELOP LATE.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
TUESDAY AND TUESDAY NIGHT...THE PATTERN ALOFT WILL BE QUITE
NEBULOUS AND SUMMERLIKE WITH THE FORECAST AREA UNDER A RIDGE THAT
EXTENDS NORTH AND NORTHWEST BACK TOWARD THE UPPER MIDWEST. AT THE
SURFACE...HIGH PRESSURE OVER THE ATLANTIC WILL EXTEND INTO GEORGIA
AND THE CAROLINAS LEADING TO A PREVAILING EASTERLY FLOW THROUGH
THE DAY. OVERNIGHT...WINDS WILL TURN MORE NORTHEASTERLY WITH TIME
AS AN AREA OF LOW PRESSURE BEGINS TO DEVELOP TO THE SOUTH AND
COASTAL TROUGH BECOMES BETTER DEFINED ALONG THE COAST. LAND AREAS
ARE EXPECTED TO BE DRY ON TUESDAY...THANKS TO PLENTY OF MID/UPPER
LEVEL DRY AIR AND WARM MID LEVELS. THERE MAY BE ISOLATED SHOWERS
OVER PORTIONS OF THE COASTAL WATERS WITHIN SOME WEAK SURFACE
CONVERGENCE...BUT ANY ACTIVITY THAT DEVELOPS WILL REMAIN OFFSHORE.
OVERNIGHT...MUCH OF THE COLUMN REMAINS QUITE DRY AND THE
DEVELOPING LOW IS STILL LOCATED WELL TO THE SOUTH.
THEREFORE...LAND AREAS ARE DRY AND THE FORECAST IS GENERALLY
QUIET. TUESDAY HIGHS WILL BE HELD IN CHECK THANKS TO THE
PREVAILING EASTERLY FLOW AND TEMPERATURES ARE EXPECTED TO TOP OUT
IN THE LOW 80S AWAY FROM THE IMMEDIATE COAST. OVERNIGHT...LOOK FOR
UPPER 50S TO LOW 60S.

WEDNESDAY THROUGH THURSDAY...THE DETAILS OF THE FORECAST WILL
ULTIMATELY BE DETERMINED BY THE EVENTUAL TRACK AND STRENGTH OF A
SURFACE LOW THAT DEVELOPS OFF THE FLORIDA EAST COAST/NORTHERN
BAHAMAS. OVERALL MODEL AGREEMENT HAS IMPROVED SIGNIFICANTLY...THOUGH
NOTABLE DIFFERENCES REMAIN WITH REGARDS TO PROXIMITY TO THE COAST
AND POTENTIAL IMPACTS FROM THE SYSTEM. THERE HAS BEEN A CLEAR
WESTWARD TREND...FIRST IN THE LOCATION OF SURFACE LOW
DEVELOPMENT...SECOND IN THE TRACK PROXIMITY TO THE SOUTHEAST COAST.
THE NAM/GFS/ECMWF OFFER THREE DIFFERENT SOLUTIONS...WITH THE GFS
BEING THE FURTHEST WEST AND THE ECMWF BEING THE FURTHEST EAST. IN
FACT...THE 00Z GFS TAKES THE CENTER OF THE LOW TO JUST OFF THE
CHARLESTON COUNTY COAST BY LATE THURSDAY. IT ALSO REMAINS UNCLEAR IF
CONDITIONS WILL BE SUPPORTIVE OF THIS SYSTEM TRANSITIONING TO
SUBTROPICAL OR TROPICAL...ESPECIALLY GIVEN THE EARLY MAY SEA SURFACE
TEMPERATURES IN THE UPPER 70S WITHIN THE GULF STREAM AND BEYOND. THE
NATIONAL HURRICANE CENTER CONTINUES TO ADVERTISE A 30 PERCENT CHANCE
OF THE SYSTEM ACQUIRING SUBTROPICAL CHARACTERISTICS. BASED ON THE
WESTWARD TREND IN THE MODELS...THE FORECAST HAS BEEN ADJUSTED TO
FEATURE HIGHER POPS MAINLY ALONG THE COAST WITH COOLER TEMPERATURES.
AT THE VERY LEAST...IT APPEARS WE WILL BE DEALING WITH AN INCREASED
RISK OF RIP CURRENTS AND THE POTENTIAL FOR SOME BEACH EROSION WITH
THE PERSISTENT NORTHEAST TO NORTHERLY WINDS AROUND THE LOW. STAY
TUNED FOR FORECAST UPDATES ESPECIALLY AS MODEL AGREEMENT HOPEFULLY
INCREASES.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
THERE CONTINUES TO BE MUCH UNCERTAINTY IN THE LONG
TERM PERIOD THANKS TO THE PRESENCE OF THE AFOREMENTIONED SURFACE LOW
NEAR THE COAST. THOUGH THE MODELS HAVE COME INTO BETTER AGREEMENT
THERE ARE STILL SIGNIFICANT DIFFERENCES THAT HAVE A SIGNIFICANT
IMPACT ON THE FORECAST. DUE TO THE WESTWARD TREND IN THE MODEL
GUIDANCE...POPS HAVE BEEN INCREASED BUT CONFIDENCE IS STILL LOW
ENOUGH TO KEEP POPS IN THE CHANCE RANGE AT BEST. OTHER THAN THE
GFS...THE CONSENSUS IS FOR THE LOW TO PULL AWAY TO THE EAST AND
NORTHEAST THROUGH THE WEEKEND AND EARLY NEXT WEEK. THIS WOULD ALLOW
FOR A WARMING TREND IN TEMPERATURES WITH THE POSSIBILITY FOR DIURNAL
CONVECTION.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 12Z TUESDAY.
LOW PROBABILITY FOR BRIEF VSBY RESTRICTIONS IN GROUND FOG TOWARDS
DAYBREAK.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
WEDNESDAY. CHANCES FOR FLIGHT RESTRICTIONS THEN INCREASE AS AN AREA
OF LOW PRESSURE TRACKS NEAR THE COAST THROUGH THE LATTER PART OF THE
WEEK.

&&

.MARINE...
TODAY...A WEAK PRESSURE PATTERN AND LIGHT/VARIABLE WINDS TO START
WILL GIVE WAY TO ONSHORE WINDS...ENHANCED TO SOME DEGREE BY THE
SEA BREEZE THIS AFTERNOON. WINDS SHOULD REMAIN LESS THAN 15
KT...ACCOMPANIED BY SEAS 2-4 FT...HIGHEST BEYOND 20 NM.

EAST WINDS LESS THAN 20 KT AND SEAS 2-4 FT ARE EXPECTED TONIGHT.

TUESDAY THROUGH FRIDAY...THE MAIN FORECAST PROBLEM REVOLVES
AROUND AN AREA OF LOW PRESSURE EXPECTED TO DEVELOP OFF THE EAST
COAST OF FLORIDA ON WEDNESDAY AND TRACK NORTH THROUGH THE END OF
THE WEEK...EVENTUALLY DRAWING CLOSER TO THE COAST. EVENTUAL MARINE
IMPACTS WILL ULTIMATELY BE DETERMINED BY THE PROXIMITY TO THE
COAST AND THE STRENGTH OF THE SYSTEM. ALSO...THE NATIONAL
HURRICANE CENTER CONTINUES TO ADVERTISE A 30 PERCENT CHANCE THAT
THE SYSTEM COULD ACQUIRE SOME SUBTROPICAL CHARACTERISTICS LATE IN
THE WEEK. REGARDLESS...BEGINNING WEDNESDAY NIGHT AND CONTINUING
THROUGH FRIDAY...THE GRADIENT WILL TIGHTEN ACROSS THE COASTAL
WATERS LEADING TO AT LEAST LIKELY SMALL CRAFT ADVISORY WINDS.
GALES WILL BE POSSIBLE AS WELL...DEPENDING ON THE PROXIMITY OF THE
LOW. SEAS WILL RAMP UP DURING THE LATTER PART OF THE WEEK THANKS
TO THE STRENGTHENING WINDS AND SWELL ENERGY ASSOCIATED WITH THE
LOW. MODELS HAVE TRENDED FURTHER WESTWARD RECENTLY...AND FURTHER
TRENDS WILL HAVE TO BE MONITORED IN THE COMING DAYS.

RIP CURRENTS... AN ELEVATED RISK FOR RIP CURRENTS IS EXPECTED
ESPECIALLY LATER THIS WEEK AND THIS WEEKEND AS A SURFACE LOW MOVES
NEAR THE COAST. INCREASING SWELL ENERGY AND COASTAL WINDS ASSOCIATED
WITH THE LOW WILL BE THE MAIN CAUSES FOR THE INCREASED RIP CURRENT
RISK.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...ECT
SHORT TERM...BSH/SPR
LONG TERM...BSH
AVIATION...ECT
MARINE...BSH/ECT/SPR



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