Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 301328
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
928 AM EDT SAT MAY 30 2015

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE OFF THE SOUTHEAST COAST WILL MOVE
INLAND LATER THIS MORNING AND THIS AFTERNOON. HIGH PRESSURE WILL
THEN RETURN SUNDAY AND PERSIST UNTIL A COLD FRONT MOVES INTO THE
AREA AND STALLS MID WEEK. LOW PRESSURE COULD MOVE NORTHWARD ALONG
OR NEAR THE COAST LATER NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
MID-MORNING WATER VAPOR IMAGERY SHOWS A WELL-DEFINED VORTICITY
MAXIMUM LOCATED ABOUT 145 NM EAST OF THE SAVANNAH RIVER ENTRANCE.
THIS FEATURE IS SLOWLY DRIFTING TO THE SOUTHWEST AROUND THE
SOUTHERN PERIPHERY OF A MID-LEVEL ANTICYCLONE THAT IS POSITIONED
OVER THE MID-ATLANTIC STATES. THE IMPULSE IS SUPPORTING NUMEROUS
SHOWERS AND A FEW TSTMS OVER THE COASTAL WATERS THIS MORNING ALONG
A VERY WEAK COASTAL TROUGH THAT IS LOCATED JUST THE BEACHES. THIS
CONVECTION WILL GRADUALLY WANE THROUGH THE REMAINDER OF THE
MORNING AS DIURNAL HEATING INTENSIFIES OVER LAND AREAS AND LOW-
LEVEL CONVERGENCE SHIFTS WEST WITH THE DEVELOPING SEA BREEZE
CIRCULATION. BOTH RADAR AND VISIBLE SATELLITE DATA ALREADY SHOW
TOWERING CUMULUS FORMING ALONG A RAPIDLY DEVELOPING SEA BREEZE
WITH CONVECTION HAVING RECENTLY INITIATED FROM ROUGHLY BEAUFORT
SOUTH ALONG THE GEORGIA COAST WHERE DIFFERENTIAL POSITIVE
VORTICITY ADVECTION ASSOCIATED WITH VORTICITY MAXIMUM OFFSHORE IS
ALREADY JUXTAPOSED WITH THE SEA BREEZE.

AS THE SEA BREEZE MOVES INLAND THE VORTICITY MAX OFFSHORE MEANDERS
FARTHER TO SOUTHWEST, THERE SHOULD BE A NOTABLE INCREASE IN
CONVECTION AWAY FROM THE COAST THIS AFTERNOON, ESPECIALLY ACROSS
INTERIOR SOUTHEAST GEORGIA AND UP INTO THE HAMPTON AND WALTERBORO
AREAS OF SOUTHEAST SOUTH CAROLINA. MODIFIED SOUNDINGS YIELD ONLY
MODEST INSTABILITY (SBCAPE 2000 J/KG, LIFTED INDEX -4 TO -5C),
BUT WITH 0-6KM BULK SHEAR AVERAGING 10 KT OR LESS, THE CONVECTIVE
MODE WILL BE PRIMARY CHARACTERIZED BY WEAK TO MODERATE AND FAIRLY
TRANSIENT UPDRAFTS. THE RISK FOR SEVERE WEATHER IS LOW, BUT A
NOTABLE INTRUSION OF DRY AIR IN THE MID- LEVELS COULD SUPPORT A
FEW LOCALLY STRONG WIND GUSTS. CONVECTION SHOULD GENERALLY WANE BY
LATE MORNING/EARLY AFTERNOON OVER THE CHARLESTON METRO AREA AS
SUBSIDENCE IN THE WAKE OF THE VORTICITY MAX OVERSPREADS THAT AREA
AND LOW-LEVEL CONVERGENCE WITH THE SEA BREEZE SHIFTS INLAND.

FOR THE LATE MORNING UPDATE...MODIFIED HOURLY POPS SLIGHTLY PER
GOING CURRENT RADAR AND SHORT TERM MODEL TRENDS. MAINTAINED
MAXIMUM POPS OF 30-50 PERCENT--HIGHEST INTERIOR SOUTHEAST
GEORGIA--GIVEN THE TRANSIENT NATURE OF THE CONVECTION. HIGHS IN
THE MID-UPPER 80S LOOK REASONABLE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
TONIGHT...ATLANTIC HIGH PRESSURE WILL BUILD INTO THE REGION. THERE
IS SOME INDICATION THAT WEAK LOW LEVEL CONVERGENCE COULD DEVELOP
ALONG AND/OR JUST OFF THE GEORGIA COAST LATER TONIGHT.
ISOLATED SHOWERS/THUNDERSTORMS COULD LINGER WEST OF THE I-95
CORRIDOR INTO EARLY EVENING...THEN DISSIPATE AS THE SEA BREEZE
SHIFTS WEST OF THE AREA AND WITH THE LOSS OF DIURNAL HEATING.
ISOLATED SHOWERS AND THUNDERSTORMS COULD THEN DEVELOP WITHIN THE
AREA OF LOW LEVEL CONVERGENCE LATE TONIGHT AND AFFECT PORTIONS OF
THE UPPER GEORGIA COAST. LOW TEMPERATURES SHOULD BE IN THE MID AND
UPPER 60S INLAND...WITH LOWER 70S NEAR THE IMMEDIATE COAST.

SATURDAY THROUGH TUESDAY...HIGH PRESSURE WEAKENS THROUGH THE
PERIOD AS AN UPPER TROUGH DEEPENS OVER THE GULF COAST REGION.
MEANWHILE...A COLD FRONT WILL MOVE TOWARD THE AREA FROM THE NORTH
AND WEST WITH DEEP MOISTURE ADVECTING NORTHWARD FROM FLORIDA. THIS
WILL RESULT IN SLIGHTLY HIGHER THAN NORMAL RAIN CHANCES MUCH OF
THE PERIOD WITH TEMPS A BIT ABOVE NORMAL. INCREASING INSTABILITY
BY MONDAY AND TUESDAY COULD YIELD A FEW STRONGER TO POSSIBLY
SEVERE STORMS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
UNSETTLED WEATHER ON TAP THROUGH MOST OF THE REST OF THE WEEK WITH A
STALLING FRONT OVER THE AREA AND POSSIBLE LOW PRESSURE SOMEWHERE
AROUND THE SOUTHEAST U.S. COAST. THUS...RAIN CHANCES SHOULD BE ABOVE
NORMAL WITH TEMPERATURES LIKELY COOLING OFF A BIT TOWARD THE END OF
THE WEEK...ESPECIALLY IF LOW PRESSURE TRACKS CLOSE TO THE LOCAL
AREA.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
VFR CONDITIONS ARE GENERALLY EXPECTED TO PREVAIL AT KCHS AND KSAV
THROUGH 12Z SUNDAY. THE INLAND PROGRESSION OF A WEAK COASTAL
TROUGH WILL ALLOW ISOLATED TO SCATTERED SHOWERS TO DEVELOP THIS
MORNING...BEFORE SHIFTING INLAND OF THE TERMINALS BY MID-
AFTERNOON WITH THE SEA BREEZE. HAVE MAINTAINED MENTION OF VICINITY
SHOWERS AT BOTH TERMINALS...BUT WITH A GREATER COVERAGE OF SHOWERS
EXPECTED NEAR KSAV HAVE ALSO INCLUDED A TEMPO GROUP THERE FOR
SHOWERS WITH MVFR CEILINGS/VISIBILITIES FROM 14-18Z. GUSTY
SOUTHEAST WINDS ARE THEN EXPECTED AT THE TERMINALS FROM MID-
AFTERNOON TO EARLY EVENING BEHIND THE SEA BREEZE.

EXTENDED AVIATION OUTLOOK...MAINLY VFR. SMALL CHANCE FOR FLIGHT
RESTRICTIONS WITHIN MOSTLY LATE MORNING/EARLY AFTERNOON SHRA AND
TSRA THROUGH WED.

&&

.MARINE...
TODAY...AN INVERTED TROUGH OVER THE COASTAL WATERS WILL RETROGRADE
AND EVENTUALLY SHIFT INLAND LATE THIS MORNING INTO THIS AFTERNOON.
AS THIS OCCURS...EASTERLY WINDS WILL VEER A BIT MORE TO THE
SOUTHEAST THIS AFTERNOON. WIND SPEEDS WILL GENERALLY BE LESS THAN
15 KT OVER THE OPEN ATLANTIC WATERS...BUT BECOME ENHANCED UPWARDS
OF 15-17 KT NEAR THE LAND/SEA INTERFACE AS THE SEA BREEZE
CIRCULATION DEVELOPS THIS AFTERNOON. THE MAJORITY OF THE WAVE
ENERGY WILL BE A 9-11 SECOND SWELL AROUND 3 OR 4 FT...ATOP A SHORT
PERIOD WIND WAVE. SIGNIFICANT WAVE HEIGHTS WILL AVERAGE 3-4 FT
ACROSS THE NEAR SHORE WATERS AND 4-5 FT ACROSS THE GEORGIA
OFFSHORE WATERS THROUGH THE DAY.

TONIGHT...ATLANTIC HIGH PRESSURE WILL MAINTAIN SOUTHEAST WINDS
GENERALLY AROUND 10 KT OR LESS. WIND SPEEDS SHOULD DIMINISH A BIT
AS THE NIGHT PROGRESSES DUE TO A WEAKENING SURFACE PRESSURE
GRADIENT. SEAS SHOULD ALSO GRADUALLY SUBSIDE BY ABOUT A FOOT OR SO
BY LATE TONIGHT.

SUNDAY THROUGH THURSDAY...ATLANTIC HIGH PRESSURE IN CONTROL INTO
TUESDAY BEFORE A COLD FRONT LIKELY PUSHES SOUTH INTO THE AREA
WEDNESDAY AND THEN STALLS INTO THURSDAY. MEANWHILE A TROUGH OF LOW
PRESSURE OVER THE WESTERN CARIBBEAN/NEAR FLORIDA COULD STRENGTHEN
INTO A LOW AND BEGIN TO MOVE NORTH TOWARD THE END OF THE PERIOD.
CONDITIONS COULD BE WORSE THAN CURRENTLY DEPICTED THURSDAY
DEPENDING ON THE STRENGTH AND POSITION OF THE LOW.

RIP CURRENTS...PERSISTENT ONSHORE FLOW WILL RESULT IN AN ELEVATED
RISK OF RIP CURRENTS. A MODERATE RISK OF RIP CURRENTS WILL BE IN
EFFECT FOR ALL BEACHES TODAY.

&&

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

&&

$$

ST



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