Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 011442
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1042 AM EDT TUE SEP 1 2015

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE WILL PERSIST OVER THE SOUTHEAST THIS
WEEK. THIS WEEKEND INTO EARLY NEXT WEEK...HIGH PRESSURE WILL BUILD
INTO THE REGION FROM THE NORTH...AND A TROUGH OF LOW PRESSURE WILL
DEVELOP OVER OR CLOSE TO COASTAL WATERS.

&&

.NEAR TERM /THROUGH TONIGHT/...
FOR THE LATE MORNING UPDATE THE FORECAST REMAINS LARGELY
UNCHANGED EXCEPT FOR VERY MINOR ADJUSTMENTS...PRIMARILY TO
TEMPERATURE AND DEWPOINT TRENDS...BUT MAXIMUM TEMPS ARE EXPECTED
TO REMAIN AS PREVIOUSLY FORECAST. WE HAVE MODIFIED THE WINDS TO
SHOW A SLIGHTLY LATER ONSET OF THE SEABREEZE AND TO DEPICT WINDS
VEERING INTO THE SEABREEZE BASED ON A STRONG CONSENSUS OF THE
LATEST HIGH RESOLUTION MODEL GUIDANCE.

THE PLUME OF DEEP TROPICAL MOISTURE AND THE ASSOCIATED STRONG
MOISTURE GRADIENT ON IT/S NORTH FLANK ACROSS EAST CENTRAL GEORGIA
AND SOUTH CAROLINA WILL DRIFT VERY SLOWLY N LATE TODAY AND
TONIGHT. IN COMBINATION WITH THE SUBTROPICAL RIDGE...THIS PATTERN
IS RESPONSIBLE FOR INCREASES IN CLOUDS AND SCATTERED SHOWERS
ACROSS SE GEORGIA ALONG THE COAST AND MAINLY SOUTH OF I-16
TODAY...AND RADAR AND SATELLITE TRENDS CURRENTLY DEPICT THIS WELL.
LATER...THERE MAY BE A FEW DOWNPOURS CLOSER TO THE ALTAMAHA RIVER
WITH CONVECTION THIS AFTERNOON DRIVEN MAINLY BY THE SEABREEZE BUT
OVERALL INSTABILITY IS MEAGER TO THE SOUTH AND ANY SHOWERS ARE
EXPECTED TO QUICKLY DISSIPATE WITH THE LOSS OF INSOLATION THIS
EVENING.

ACROSS MUCH OF SE SOUTH CAROLINA...MAINLY DRY WEATHER IS LIKELY
TODAY AS PWATS ARE LOWER BUT MAINTAINED A SLIGHT AFTERNOON CHANCE
FOR MOSTLY SPOTTY AND SHALLOW CONVECTION ALONG THE SEA BREEZE
GIVEN A SLOWLY NORTHWARD ADVANCING MOISTURE FLUX ACROSS ADJACENT
WATERS.

TONIGHT...MODELS INDICATE DECREASING CONDENSATION PRES DEFICITS
INTO SE GEORGIA ALONG WITH WEAK UPPER DIFLUENCE AND THIS COULD
RESULT IN ISOLATE TO SCATTERED SHOWERS AND PERHAPS A FEW TSTMS
ACROSS SE GEORGIA WITH ISOLATED SHOWERS COASTAL SOUTH CAROLINA.
MODELS INDICATE PWATS WILL SURGE ABOVE 2.3 INCHES THUS WE
BUMPED POPS UP A BIT SOUTHERN ZONES.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
WEDNESDAY...A SHORTWAVE WILL TRACK ACROSS SOUTHERN COUNTIES OF THE
FORECAST AREA. WHILE MODELS DIFFER SOMEWHAT REGARDING
ORIENTATION/TIMING OF THIS FEATURE...IN GENERAL THE SCENARIO FAVORS
A NORTH TO SOUTH GRADIENT OF POPS...WITH A MAXIMUM OF ABOUT 50
PERCENT SOUTH OF I-16. PWATS EXCEEDING 2 INCHES AND WEAK LOW/MID
LEVEL WINDS SUGGEST A POTENTIAL FOR LOCALLY EXCESSIVE RAINFALL
ACROSS THIS AREA...AND LOCALLY GREATER POPS COULD EVENTUALLY BE
REQUIRED. OTHERWISE...TEMPERATURES SHOULD RECOVER INTO THE
UPPER80S/LOWER 90S MOST AREAS.

WEDNESDAY NIGHT...THE SHORTWAVE SHOULD PUSH OFFSHORE...ALTHOUGH
MODELS CONTINUE TO DISAGREE REGARDING THIS SCENARIO. THE 01/00Z EURO
MAINTAINS A FAIRLY WELL DEFINED AND PROGRESSIVE SYSTEM...WHILE THE
01/00Z GFS AND TO A LESSER EXTENT THE NAM DEPICT AN ELONGATED AXIS
OF VORTICITY WHICH PERSISTS OVER THE REGION WELL INTO THE NIGHT. THE
LATEST FORECAST DEPICTS DECREASING POPS WITH TIME...WITH OVERNIGHT
SLIGHT CHANCE/CHANCE POPS LIMITED TO SOUTHERN COASTAL COUNTIES AND
ADJACENT COASTAL WATERS. BY DAYBREAK THURSDAY...EXPECT LOWS IN THE
LOWER 70S INLAND AND IN THE MID/UPPER 70S CLOSER TO THE COAST.

THURSDAY...SUBSIDENCE/SHORTWAVE RIDGING IN THE WAKE OF THE DEPARTING
SHORTWAVE TROUGH SHOULD LIMIT DIURNAL POPS AND ALLOW TEMPERATURES TO
RECOVER INTO THE LOWER/MID 90S AWAY FROM THE COAST. MAX HEAT INDEX
VALUES OF 98-102F WILL BE COMMON THURSDAY AFTERNOON. POPS ARE
LIMITED TO SLIGHT CHANCE/CHANCE...MAINLY ALONG THE SEA BREEZE AND
HIGHEST ACROSS THE SOUTH...BUT EVEN THESE POPS COULD PROVE TO BE A
BIT HIGH.

THURSDAY NIGHT...POPS ARE LIMITED TO COASTAL WATERS. EXPECT LOW
TEMPERATURES IN THE LOWER-MID 70S INLAND AND MID TO UPPER 70S NEAR
THE COAST...EVEN AROUND 80F ON THE BEACHES.

FRIDAY...AN UPPER TROUGH WILL PUSH INTO THE REGION FROM THE NORTH
AND/OR WEST...DEPENDING ON YOUR MODEL OF CHOICE. POPS SHOULD
INCREASE INTO THE 30-40 PERCENT RANGE...ESPECIALLY DURING THE
AFTERNOON/EVENING. HIGH TEMPERATURES IN THE UPPER 80S WILL BE
COMMON.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AT THE SURFACE...EXPANSIVE HIGH PRESSURE CENTERED NORTH OF THE
REGION WILL BUILD SOUTH NEXT WEEKEND INTO EARLY NEXT WEEK...AND A
COASTAL TROUGH SHOULD DEVELOP. ALOFT...A COMPLEX BLOCKING PATTERN
WILL DEVELOP...AND MEDIUM RANGE MODELS GENERALLY AGREE THAT THE
UPPER TROUGH WILL BECOME CUT OFF OVER THE SOUTHEAST THIS WEEKEND AND
WILL MEANDER OVER THE REGION INTO EARLY NEXT WEEK. THIS PATTERN
SHOULD FAVOR SLIGHTLY BELOW NORMAL TEMPS AND ABOVE NORMAL POPS.
UNCERTAINTY EXISTS REGARDING THE RELATIVE POSITIONS/STRENGTHS OF
CRITICAL FEATURES INCLUDING THE NORTH-SOUTH MOISTURE GRADIENT WHICH
TYPICALLY DEVELOPS IN THESE PATTERNS. THUS...CHANCE POPS ARE IN ORDER
DURING THE DAYTIME HOURS...HIGHEST SOUTH AND OVER COASTAL
WATERS...AND NIGHTTIME POPS ARE FOCUSED ACROSS SOUTHERN/COASTAL
COUNTIES AND ACROSS COASTAL WATERS. FORECAST ADJUSTMENTS WILL BE
NECESSARY AS DETAILS EMERGE OVER THE NEXT SEVERAL DAYS.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL AT BOTH TERMINALS THROUGH 12Z
WEDNESDAY. MOISTURE WILL BECOME A DEEPER AT KSAV LATER TODAY AND
ESPECIALLY TONIGHT. MVFR CIGS POSSIBLE ARE POSSIBLE LATE TONIGHT
AT KSAV ALONG WITH A FEW SHOWERS BUT PROBABILITIES ARE RATHER LOW
AT THIS POINT.

EXTENDED AVIATION OUTLOOK THROUGH SUNDAY...MAINLY VFR. THE
PROBABILITY FOR FLIGHT RESTRICTIONS WILL INCREASE THIS WEEKEND.

&&

.MARINE...
TODAY A WEAK PRESSURE PATTERN WILL PERSIST WITH SYNOPTIC FLOW
FAVORING A MAINLY SSE TO SSW COMPONENT. IN THE NEARSHORE WATERS A
LAND BREEZE WILL SHORTLY GIVE WAY TO A COMBINATION OF THIS
SYNOPTIC FLOW WITH A SEABREEZE LATER. SPEEDS MAINLY 10 KT OR LESS
AND SEAS 2 TO 3 FT THROUGH TONIGHT.

THROUGH LATE WEEK...A WEAK PRESSURE PATTERN WILL TRANSLATE
TO WINDS LESS THAN 15 KT DOMINATED BY THE SEA AND LAND BREEZES. BY
NEXT WEEKEND...HIGH PRESSURE BUILDING FROM THE NORTH AND A
DEVELOPING COASTAL TROUGH COULD PRODUCE INCREASING NE WINDS AND
BUILDING SEAS.

RIP CURRENTS...AN ELEVATED RISK FOR RIP CURRENTS COULD DEVELOP AGAIN
NEXT WEEKEND.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...SPR


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