FXUS62 KCHS 290804
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
304 AM EST SUN NOV 29 2009

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT OFF THE COAST TODAY THROUGH MONDAY. 
A COLD FRONT WILL MOVE INTO THE AREA FROM THE NORTHWEST MONDAY
NIGHT...THEN STALL SOUTH OF THE AREA ON TUESDAY. A GULF LOW
PRESSURE SYSTEM WILL DEVELOP TUESDAY AND MOVE THROUGH THE MIDLANDS 
ON WEDNESDAY. THE STORM SYSTEM WILL SHIFT OFF THE MID ATLANTIC 
COAST WEDNESDAY NIGHT...FOLLOWED BY HIGH PRESSURE FOR LATE 
IN THE WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
HIGH PRESSURE CENTERED ALONG THE SOUTH CAROLINA COAST WILL SHIFT
OFFSHORE TODAY AS WEAK RIDGING ALOFT BREAKS DOWN AND IS REPLACED
WITH A STRENGTHENING ZONAL FLOW. A WEAK RETURN FLOW ON THE BACKSIDE
OF THE DEPARTING HIGH WILL SUPPORT A WARMER DAY COMPARED TO THE
PAST SEVERAL WITH HIGHS PUSHING 70 DEGREES IN A NUMBER OF AREAS.
CONDITIONS WILL FAVOR THE DEVELOPMENT OF A WEAK RESULTANT SEA
BREEZE ALONG THE BEACHES BY EARLY AFTERNOON WHICH WILL MAKE A
SLOW INLAND TREK THROUGH SUNSET. WATER TEMPERATURES OFF THE BEACHES
ARE GENERALLY IN THE UPPER 50S TO AROUND 60 SO EXPECT THE BEACHES
TO REMAIN CONSIDERABLY COOLER WITH TEMPERATURES LIKELY STRUGGLING
TO REACH 63-65 DEGREES. SATELLITE SHOWS THE BACKSIDE OF THE MAIN
CIRRUS SHIELD PUSHING INTO SOUTHERN ALABAMA AND THE FAR WESTERN
FLORIDA PANHANDLE. 29/00Z 300-400MB LAYERED RH PROGS CAPTURE
CURRENT SATELLITE TRENDS WELL AND SHOW THE CIRRUS THINNING FROM
SOUTHWEST TO NORTHEAST AS THE AFTERNOON PROGRESSES. WILL GO WITH
PARTLY CLOUDY SKIES THIS MORNING WITH SKIES SLOWLY BECOMING MOSTLY
CLEAR FROM EARLY AFTERNOON ON.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM MONDAY/...
THE WESTERN FLANKS OF DEPARTING HIGH PRESSURE WILL HOLD OVER THE
REGION TONIGHT AS A COLD FRONT APPROACHES FROM THE WEST. JET
ENHANCED CIRRUS WILL SLOWLY INCREASE AFTER MIDNIGHT AS A STRONG
SUBTROPICAL JET STRENGTHENS FROM THE LOWER MISSISSIPPI VALLEY INTO
THE MIDDLE ATLANTIC REGION. IT LOOKS LIKE THE CIRRUS WILL REMAIN
RATHER THIN FOR MUCH OF THE NIGHT SO WILL STICK WITH A MOSTLY
CLEAR FORECAST FOR NOW AND MONITOR TRENDS FOR A POSSIBLE ADJUSTMENT
UPWARDS INTO THE PARTLY CLOUDY CATEGORY. OVERNIGHT LOWS WILL BE
TEMPERED SOMEWHAT BY THE INCREASING CIRRUS ALOFT AS WELL AS A
STRENGTHENING PRE-FRONTAL LOW-LEVEL JET. EXPECT LOWS FROM THE MID
40S WELL INLAND TO THE MID 50S AT THE BEACHES.

A POTENT NORTHERN STREAM SHORTWAVE MOVING ACROSS THE UPPER
MISSISSIPPI VALLEY WILL DIG ACROSS THE OHIO AND TENNESSEE VALLEYS
MONDAY. ITS ATTENDANT COLD FRONT WILL APPROACH FROM THE NORTHWEST
MONDAY AND PUSH OFFSHORE SHORTLY AFTER SUNSET. DESPITE FAVORABLE
UPPER DYNAMICS ASSOCIATED THE RIGHT ENTRANCE REGION OF THE UPPER
JET...MEAGER LOW-LEVEL MOISTURE RETURN AHEAD OF THE SURFACE FRONT
SUGGESTS ANY FRONTAL BAND SHOWERS WILL LIKELY HAVE A HARD TIME
MOVING MUCH PAST THE CENTRAL SOUTH CAROLINA MIDLANDS AND EAST
CENTRAL GEORGIA. THIS IS REFLECTED RATHER WELL BY THE LATEST SREF
MEAN WHICH SHOWS VERY LOW PROBABILITIES FOR MEASURABLE RAINFALL
OVER EASTERN SOUTH CAROLINA AND GEORGIA. WILL KEEP SLIGHT CHANCE
POPS IN TACT FROM MID AFTERNOON ON ACROSS MAINLY THE FAR WESTERN
AND NORTHERN AREAS AS A FEW SHOWERS CAN NOT BE COMPLETELY RULED
OUT THERE PRIOR TO SUNSET. HIGHS WILL ONCE AGAIN REACH INTO THE
LOWER 70S EXCEPT ALONG THE COAST WHERE ANOTHER WEAK RESULTANT WILL
KEEP TEMPERATURES AT THE BEACHES CONSIDERABLY COOLER.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
LATEST MODEL RUNS CONTINUE TO TREND TOWARD A WEAKER FRONTAL SYSTEM
MONDAY NIGHT...AND WILL KEEP RAIN CHANCES ONLY IN THE SLIGHT
CHANCE RANGE AS THE FRONT SHIFTS SOUTHEAST ACROSS THE AREA. WINDS
WILL VEER TO THE NORTH WITHIN BUILDING HIGH PRESSURE BEHIND THE
FRONT...SUPPORTING RELATIVELY COOLER TEMPERATURES ON TUESDAY WITH
HIGHS IN THE MID 60S.

THE MAIN FORECAST CONCERN DURING THE EXTENDED PERIOD REMAINS THE
POTENT GULF LOW SYSTEM THAT WILL DEVELOP ON TUESDAY AND SHIFT
NORTHEAST ACROSS THE MIDLANDS TOWARD THE MID ATLANTIC STATES.
THERE ARE SOME VARIATIONS BETWEEN THE ECMWF AND GFS IN THE
PLACEMENT OF THE DOMINANT SURFACE LOW. HOWEVER CONSENSUS CONTINUES
TO BE TOWARD A MORE INLAND TRACK...WITH THE BEST CHANCE FOR HEAVY
RAIN ACROSS CENTRAL/NORTHERN GEORGIA AND THE SOUTH CAROLINA
MIDLANDS.

THE LINGERING FRONT TO THE SOUTH WILL LIFT NORTH AS A WARM FRONT
AHEAD OF THE SYSTEM TUESDAY NIGHT...WITH RAIN CHANCES INCREASING
FROM SOUTHWEST TO NORTHEAST. BY WEDNESDAY...RAIN CHANCES WILL
INCREASE TO LIKELY...AS SOUTHEAST SOUTH CAROLINA AND SOUTHEAST
GEORGIA FALL WITHIN STRONG WARM ADVECTION. DYNAMICS ASSOCIATED
WITH THIS SYSTEM ARE QUITE IMPRESSIVE...WITH STRONG WINDS FIELDS
AND PLENTY OF VORT ENERGY FROM THE NEGATIVELY TILTED UPPER SHORTWAVE.
LATEST MODEL RUNS CONTINUE TO LIMIT INSTABILITY...AND AM HESITANT
TO MENTION MORE THAN A SLIGHT CHANCE FOR THUNDER OVER LAND AREAS
ON WEDNESDAY. PERHAPS OF GREATER CONCERN WILL BE HEAVY RAIN POTENTIAL
COINCIDENT WITH ASTRONOMICAL HIGH TIDES. SUBSEQUENT FORECASTS MAY
NEED TO INCLUDE MENTION OF HEAVY RAINFALL AND POSSIBLE COASTAL
FLOOD CONCERNS.

ECMWF SOLUTION IS STILL SLOWER WITH TRACKING THE LOW PRESSURE 
NORTHEAST THAN THE GFS...HOWEVER BOTH MODELS INDICATE THE SYSTEM 
DRAGGING A COLD FRONT THROUGH THE AREA GENERALLY BY MIDDAY THURSDAY. 
HAVE DROPPED RAIN CHANCES ON THURSDAY AS A RESULT. TEMPERATURES FOR 
LATE WEEK AND INTO THE WEEKEND COULD COOL INTO THE UPPER 
50S...DEPENDING ON THE STRENGTH OF COLD ADVECTION AND BUILDING HIGH 
PRESSURE FROM THE NORTH. HAVE MAINTAINED A RAIN FREE FORECAST 
THURSDAY THROUGH THE WEEKEND AT THIS POINT.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS/KSAV THROUGH 06Z MONDAY. COULD
SEE MARGINAL LOW-LEVEL WIND SHEAR AT KCHS AFTER 04-05Z MONDAY AS
1500-2000 FT WINDS ARE FORECAST TO INCREASE TO NEAR 30 KNOTS WITH
SURFACE WINDS AOB 5 KNOTS. SITUATION LOOKS TO MARGINAL TO INCLUDE
IN THE TAF ATTM.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CIGS/VSBYS POSSIBLE 
MONDAY NIGHT THROUGH WEDNESDAY DUE TO RAIN CHANCES WITHIN
UNSETTLED WEATHER.

&&

.MARINE...
LIGHT AND VARIABLE WINDS DOMINATE THE WATERS THIS MORNING WITH
SEAS GENERALLY 1 FOOT OR LESS. WINDS WILL BECOME MORE SOUTHERLY
THIS MORNING AS HIGH PRESSURE SHIFTS FARTHER OFFSHORE AND A WEAK
RESULTANT SEA BREEZE TAKES SHAPE ALONG THE BEACHES. SPEEDS WILL
REMAIN LESS THAN 10 KNOTS TODAY WITH SEAS 1 FOOT OR LESS.

WINDS WILL GRADUALLY PICKUP TONIGHT AS A PRE-FRONTAL LOW-LEVEL JET
BEGINS TO IMPINGE ON THE LOCAL MARINE AREA. THE CORE OF THE LOW-
LEVEL LOOKS TO REMAIN NORTHWEST OF THE REGION...BUT IT WILL BE 
CLOSE ENOUGH TO SUPPORT WINDS AS HIGH AS 15-20 KT AT TIMES AFTER
MIDNIGHT FOR THE WATERS NORTH OF EDISTO BEACH. ELSEWHERE WINDS
WILL GENERALLY REMAIN 10-15 KT. SEAS WILL REMAIN 1-2 FT EXCEPT
BUILD TO 2-3 FT FOR THE CHARLESTON COUNTY COASTAL WATERS. WINDS
WILL INCREASE FURTHER ON MONDAY AS THE GRADIENT TIGHTENS WITH THE
APPROACH OF A COLD FRONT. BOTH WINDS AND SEAS WILL REMAIN BELOW
SMALL CRAFT ADVISORY THRESHOLDS...HOWEVER SPEEDS AS HIGH AS 15-20
KT CAN BE EXPECTED...WITH THE HIGHEST CONDITIONS EXPECTED FOR THE
WATERS NORTH OF EDISTO BEACH. EXPECT SEAS 2-4 FT WITH THE LOWEST
SEAS CONFINED TO THE GEORGIA NEARSHORE WATERS.

MONDAY NIGHT THROUGH THURSDAY...SOUTHERLY FLOW WILL STEADILY VEER
TO THE NORTH MONDAY NIGHT...AS A COLD FRONT SLIPS SOUTH OF THE
WATERS. TRANSIENT HIGH PRESSURE WILL MOVE NORTH OF THE AREA ON
TUESDAY...AS A POTENT LOW SYSTEM DEVELOPS OVER THE GULF OF MEXICO.
THE COASTAL WATERS WILL FALL WITHIN THE WARM SECTOR ON
WEDNESDAY...WHILE THE SURFACE LOW TRACKS FROM THE GULF COAST
STATES THROUGH THE MIDLANDS. MARINE CONDITIONS WILL DETERIORATE
RAPIDLY. THE MAIN QUESTION WILL BE WIND POTENTIAL DURING THIS
PERIOD. GFS SHOWS IMPRESSIVE WIND FIELDS WITHIN THIS STRONGLY
DYNAMIC PATTERN. ALTHOUGH 35 TO 40 KT SUSTAINED WINDS ARE
INDICATED BY THE LATEST GFS RUN...AM HESITANT TO FORECAST SUCH
STRONG SURFACE FLOW. SUBSTANTIAL WARM ADVECTION ON WEDNESDAY COULD
SUGGEST THAT THE MIXING PROFILE WILL BE LIMITED...THUS A LARGE
PORTION OF THE SURGE COULD MAINLY BE A RESULT OF THE INTENSELY
TIGHTENED PRESSURE GRADIENT. HAVE OPTED TO MAINTAIN PERSISTENCE
WITH PREVIOUS FORECAST AND CAP SUSTAINED WINDS JUST BELOW 30 KT IN
THE OUTER WATERS.

ALTHOUGH FORECASTED CONDITIONS FOR MID WEEK ARE NOT AS STRONG AS
THE GFS...MARINE CONDITIONS WILL STILL BE QUITE HAZARDOUS AND
FLAGS WILL LIKELY BE NEEDED FOR WINDS AND SEAS ACROSS MOST OF THE
COASTAL WATERS FOR WEDNESDAY INTO THURSDAY.

THE LOW SYSTEM WILL SHIFT NORTHEAST OFF THE MID ATLANTIC COAST ON
THURSDAY. EXPECT GRADUALLY IMPROVING CONDITIONS AFTER AN
ASSOCIATED COLD FRONT SHIFTS THROUGH THE WATERS AND HIGH PRESSURE
REBUILDS OVER THE REGION.

&&

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

&&

$$