646
FXUS62 KCHS 091535
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1035 AM EST TUE FEB 9 2010
SYNOPSIS
WEAK LOW PRESSURE WILL PASS EAST OF THE AREA TODAY AS A STRONG
COLD FRONT APPROACHES FROM THE WEST. THE FRONT WILL PUSH OFFSHORE
TONIGHT WITH COLD HIGH PRESSURE BUILDING IN WEDNESDAY AND THURSDAY.
ANOTHER STORM SYSTEM WILL PASS SOUTH OF THE AREA FRIDAY INTO
SATURDAY...POSSIBLY BRINGING SOME WINTER WEATHER TO THE REGION.
NEAR TERM /UNTIL 6 PM THIS EVENING/
A SUBSTANTIAL BAND OF SHOWERS AND THUNDERSTORMS HAS TAKEN SHAPE
ACROSS SOUTHERN SC ASSOCIATED WITH A WAVE OF LOW PRESSURE SHIFTING
UP THE COAST. THIS BAND APPEARS TO BE INCREASING IN COVERAGE AND
INTENSITY DUE TO IMPROVING LOW-LEVEL MOISTURE AS THE COASTAL FRONT
LIFTS NORTH. ONCE THIS BAND MOVES THROUGH...ONLY WEAK FORCING WILL
EXIST FOR LIGHT RAIN OR ISOLATED SHOWERS ACROSS THE AREA UNTIL A
COLD FRONTAL BAND MOVES INTO THE AREA THIS EVENING. TWEAKED MOST
WEATHER ELEMENTS FOR LATEST TRENDS AND EXPECTED CONDITIONS THROUGH
6 PM.
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/
ANY LINGERING SHOWERS WILL QUICKLY COME TO AN END THIS EVENING AS
A STRONG COLD FRONT SHIFTS OFFSHORE AND COLD/DRY AIR FILTERS IN
FROM THE WEST. BREEZY CONDITIONS WILL DEVELOP BEHIND THE FRONT AS
STRONG COLD AIR ADVECTION INITIATES AND PRESSURES RISE RAPIDLY
WITH ITS PASSAGE. MIXING WILL BE LIMITED SOMEWHAT GIVEN THE
UNFAVORABLE TIME OF DAY...BUT WINDS OF 15-25 MPH WITH GUSTS AS
HIGH AS 30-35 MPH CAN BE EXPECTED. ATTM SPEEDS LOOK TO REMAIN BELOW
WIND ADVISORY CRITERIA...ALTHOUGH SPEEDS COULD PUSH ADVISORY
LEVELS OVERNIGHT SHOULD AN INTENSE ISALLOBARIC RISE/FALL COUPLET
DEVELOP BETWEEN THE DEPARTING LOW AND COLD HIGH PRESSURE BUILDING
IN FROM THE WEST. TRENDS WILL BE CAREFULLY MONITORED. LOWS WILL
RANGE FROM THE UPPER 20S FAR INLAND TO THE MID 30S COAST BUT
BREEZY WEST WINDS WILL PUSH WIND CHILLS INTO THE TEENS AND LOWER
20S.
LAKE WINDS...A POTENTIALLY DANGEROUS LAKE WIND EVENT COULD UNFOLD
ON LAKE MOULTRIE TONIGHT. STRONG COLD AIR ADVECTION DEVELOPING IN
THE WAKE OF A PASSING COLD FRONT COMBINED WITH WATER TEMPERATURES
IN THE UPPER 40S TO NEAR 50 WILL YIELD IMPRESSIVE MIXING PROFILES
OVER THE OPEN LAKE WATERS WITH MIXING HEIGHTS INCREASING TO AS
HIGH AS 2000-2500 FT. MOMENTUM TRANSFER TOOLS SUGGEST ENHANCED
MIXING MECHANISMS COULD TAP INTO A BELT OF 35-40 KT WINDS JUST
OFF THE SURFACE WHICH COULD PUSH SUSTAINED WINDS AS HIGH AS 30-35
KT WITH OCCASIONAL HIGHER GUSTS. HIGH WIND WARNING CRITERIA IS 35
KT FOR 1 HOUR OR MORE. CONFIDENCE IS AT LEAST 50 PERCENT THAT THE
OPEN LAKE WATERS WILL SEE 35 KT FOR AT LEAST AN HOUR LATE TONIGHT
INTO WEDNESDAY MORNING...SO A HIGH WIND WATCH WILL BE ISSUED FOR
LAKE MOULTRIE FROM THIS EVENING UNTIL LATE WEDNESDAY MORNING.
WEST/NORTHWEST WINDS AS HIGH AS 35 KT WILL PRODUCE EXTREMELY ROUGH
CONDITIONS WITH WAVES BUILDING AS HIGH AS 4 FT...MAINLY ACROSS
THE CENTRAL AND EASTERN PARTS OF THE LAKE. THIS MAY RESULT IN SOME
MINOR DOCK DAMAGE AND POSSIBLY SOME LAKESHORE INUNDATION GIVEN THE
LAKE IS RUNNING JUST SHY OF ACTION STAGE LEVELS.
LONG TERM /WEDNESDAY THROUGH MONDAY/
THE SURFACE LOW WILL BOMB OFF THE MID ATLANTIC COAST ON WEDNESDAY
UNDER A NEGATIVELY TILTED UPPER TROUGH. STRONG COLD ADVECTION WILL
INITIATE WITH THE COLD FRONT OFFSHORE THE SOUTHEAST STATES BY
DAYBREAK WEDNESDAY. THIS COLD ADVECTION...COMBINED WITH A VERY TIGHT
PRESSURE GRADIENT...WILL SUPPORT A POSSIBLY SIGNIFICANT WIND EVENT
FOR THE FORECAST AREA. THE WIND FIELDS ARE QUITE IMPRESSIVE...WITH A
40 TO 50 KT LOW LEVEL JET LOCATED UNDER A 150 KT UPPER JET. DAYTIME
MIXING WILL BE ENHANCED BY CLEARING SKIES AND DRY AIR BEHIND THE
FRONT...LIKELY TAPPING INTO NEARLY 50 KT WINDS IN THE BOUNDARY
LAYER. A WIND ADVISORY WILL LIKELY BE ISSUED IN UPCOMING FORECAST
PACKAGES TO COVER THESE CONDITIONS. WHEN CONSIDERING POSSIBLE
IMPACTS OF THE STRONG WINDS OVER SATURATED SOIL...THERE IS SOME
CONCERN THAT TREE AND POWER LINE STABILITY WILL BE COMPROMISED. THUS
WILL ALSO BE CONSIDERING A HIGH WIND WATCH FOR WEDNESDAY.
DUE TO THE AFOREMENTIONED COLD ADVECTION...TEMPERATURES ON
WEDNESDAY WILL BE SUPPRESSED AT AROUND 50 DEGREES DESPITE FULL
SUNSHINE. WINDY CONDITIONS SUPPORT WIND CHILLS IN THE TEENS DURING
THE MORNING...RISING TO THE 40S BY THE AFTERNOON.
CONDITIONS WILL GRADUALLY MODERATE ON THURSDAY...AS BROAD HIGH
PRESSURE BUILDS BEHIND THE RETREATING LOW SYSTEM SHIFTING FAR TO THE
NORTHEAST. AFTER A COLD NIGHT IN THE 20S FOR MOST LOCATIONS AWAY
FROM THE COAST...HIGH TEMPERATURES WILL REBOUND INTO THE LOWER TO
MID 50S THURSDAY AFTERNOON.
DRY WEATHER WILL CONTINUE WILL CONTINUE ON THURSDAY...BEFORE A
SOUTHERN STREAM LOW PRESSURE APPROACHES FROM THE GULF OF MEXICO ON
FRIDAY. ALL MODELS KEEP THE SYSTEM WELL TO THE SOUTH...CROSSING
CENTRAL FLORIDA. THE FORECAST AREA WILL REMAIN IN THE COLD SECTOR
THROUGH SATURDAY...WITH THE MAIN CONCERN BECOMING PRECIP AMOUNTS AND
PRECIP TYPE ON FRIDAY. THE BEST CHANCE OF PRECIPITATION WILL BE
ACROSS SOUTHEAST GEORGIA ZONES...CLOSEST TO THE DEEP MOISTURE
ASSOCIATED WITH THE SOUTHERN LOW. HAVE INDICATED SLIGHT CHANCES FOR
PRECIPITATION NORTHERN ZONES AND A CHANCE MAINLY SOUTH OF THE
SAVANNAH RIVER.
AS THE SURFACE LOW CROSSES CENTRAL FLORIDA AND MOVES INTO THE
ATLANTIC...THE FORECAST AREA WILL FALL WITHIN COLD ADVECTION
BEHIND THE SYSTEM. ANY LINGERING MOISTURE FRIDAY NIGHT COULD POSE
A PRECIP TYPE ISSUE IN THIS COLD AIR MASS. SOUNDING ANALYSIS
INDICATES ONLY A SHORT WINDOW OF OPPORTUNITY FOR FROZEN
PRECIPITATION...WHEN THERE IS ENOUGH MOISTURE IN THE MID LEVELS TO
SUPPORT ICE CRYSTAL FORMATION AT THE SAME TIME THAT LOW LEVEL
TEMPERATURES DROP TO FREEZING. HAVE MAINTAINED MENTION OF A SLIGHT
CHANCE OF RAIN OR SNOW AFTER 00Z FRIDAY EVENING THROUGH EARLY
SATURDAY MORNING. CONFIDENCE IS LOW AT THIS TIME...AND PREFER NOT TO
EMPHASIZE IMPACTS THIS FAR IN ADVANCE.
DRY HIGH PRESSURE WILL MOVE INTO THE REGION AGAIN FOR THE
WEEKEND...ALLOWING A GRADUAL WARMING TREND FROM THE COOL
TEMPERATURES SEEN MID TO LATE WEEK.
AVIATION /15Z TUESDAY THROUGH SATURDAY/
VFR CONDITIONS WILL PREVAIL THROUGH MUCH OF THE MORNING. A WEAK
WARM FRONT IS MOVING STEADILY NORTH AND WILL MOVE THROUGH THE
TERMINALS BY MID-MORNING AS LOW PRESSURE PASSES OFFSHORE. MVFR
CIGS THAT ARE BEING OBSERVED PERIODICALLY AT KCHS SHOULD RISE
SHORTLY AS THE FRONT APPROACHES. CIGS WILL LOWER AGAIN THIS
AFTERNOON AS A STRONG COLD FRONT APPROACHES FROM THE WEST. MOST OF
THE AVAILABLE GUIDANCE STILL KEEPS THE BULK OF THE FRONTAL RAINS
WEST OF THE TERMINALS BUT BETTER CHANCES FOR SOME IMPACTS WILL BE
A KCHS...ROUGHLY 02-04Z. WILL CARRY A TEMPO 5SM -RA FOR NOW BUT
KEEP KSAV DRY BUT INDICATE MVFR CIGS AT BOTH TERMINALS. CONFIDENCE
ON SHOWER TIMING AND COVERAGE REMAINS LOW HOWEVER. THE COLD FRONT
IS ON TARGET TO CROSS THE TERMINALS AROUND 04Z WITH GUSTY WINDS
DEVELOPING IN ITS WAKE. COULD SEE GUSTS AS HIGH AS 25-30 KT AT
BOTH TERMINALS.
EXTENDED AVIATION OUTLOOK...VFR WEATHER LATE TUESDAY NIGHT THROUGH
EARLY FRIDAY...WITH PERHAPS MVFR WEATHER AGAIN LATE IN THE WEEK.
THERE WILL BE EITHER LLWS AND/OR GUSTY SURFACE WINDS LATE TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT WITH STRONG COLD AIR ADVECTION AND
EXCELLENT MIXING ACROSS THE AREA.
MARINE
EAST TO NORTHEAST WINDS WILL QUICKLY TURN SOUTH THIS MORNING AS
LOW PRESSURE APPROACHES FROM THE SOUTH AND A WEAK WARM FRONT
PUSHES NORTH ACROSS THE WATERS. SPEEDS MAY BECOME LOCALLY ENHANCED
ALONG THE CHARLESTON COUNTY COAST CLOSER TO SUNRISE AS THE
GRADIENT PINCHES SOMEWHAT AHEAD OF THE LOW. SPEEDS LOOK TO GO NO
HIGHER THAN 15 KT ATTM. 10-15 KT WILL DOMINATE ELSEWHERE TODAY
WITH SEAS GENERALLY 2-3 FT NEARSHORE...3-4 FT OFFSHORE.
DANGEROUS MARINE CONDITIONS WILL DEVELOP RAPIDLY TONIGHT AS LOW
PRESSURE PULLS AWAY FROM THE REGION AND A STRONG COLD FRONT PUSHES
OFF THE COAST. IMPRESSIVE COLD AIR ADVECTION COMBINED WITH STRONG
POST FRONTAL PRESSURE RISES WILL SUPPORT A RAPID INCREASE IN WIND
SPEEDS BY LATE EVENING. THE STRENGTH OF THE COLD AIR ADVECTION
LOOKS IMPRESSIVE AND EXPECT RELATIVELY DEEP MIXING PROFILES TO
EVOLVE DESPITE THE RELATIVELY COOL SHELF WATERS. GUIDANCE HAS BEEN
CONSISTENT FOR SEVERAL RUNS NOW IN DEVELOPING GALES OVER THE
NEARSHORE WATERS BEGINNING AS EARLY AS MID-LATE EVENING...SO THE
GALE WATCH FOR THE NEARSHORE WATERS INCLUDING THE CHARLESTON
HARBOR WILL BE UPGRADED TO A GALE WARNING.
EVEN WORSE CONDITIONS ARE EXPECTED OVER THE GEORGIA OFFSHORE
WATERS WHERE SATELLITE DERIVED WATER TEMPERATURE DATA SUGGEST THE
WESTERN WALL OF THE GULF STREAM NUDGES INTO THE WATERS BEYOND 40
NM. DATA INDICATE WATER TEMPERATURES ARE IN THE MID 60S IN THIS
AREA...WHICH CORRESPONDS WITH THE 65 DEGREE WATER TEMPERATURE
REPORTED BY 41004. EXPECT WINDS TO INCREASE TO 35-45 KT GALES
OVERNIGHT WITH FORECAST SOUNDINGS SUPPORTING A POTENTIAL FOR
FREQUENT GUST TO STORM FORCE /AT LEAST 48 KT/. AFTER A COORDINATION
CALL WITH THE LEAD FORECASTER AT THE OCEAN PREDICTION CENTER...WE
BOTH FELT IT BEST TO GO AHEAD AND FORECAST STORM FORCE WINDS
TONIGHT ALONG THE WESTERN WALL OF THE GULF STREAM WHICH WILL
NECESSITATE THE ISSUANCE OF A STORM WATCH. THE STORM WATCH WILL
EITHER BE UPGRADED TO STORM WARNING OR A GALE WARNING LATER TODAY
ONCE THE 12Z MODELS CAN BE EVALUATED.
SEAS WILL BUILD TO HAZARDOUS LEVELS TONIGHT...ESPECIALLY OFFSHORE.
EXPECT PEAK HEIGHTS OF 5-8 FT NEARSHORE WATERS /LOWER AT THE
IMMEDIATE COAST DUE TO STRONG OFFSHORE FLOW/...WITH SEAS AS HIGH
AS 15 FT BEYOND 40 NM. MARINERS ARE URGED TO REMAIN IN PORT
BEGINNING TONIGHT GIVEN THE EXTREMELY HAZARDOUS CONDITIONS THAT
ARE EXPECTED.
WEDNESDAY THROUGH SUNDAY...SIGNIFICANT MARINE WIND EVENT WILL
CONTINUE INTO WEDNESDAY. STRONG OFFSHORE WINDS WITHIN COLD
ADVECTION WILL BE ENHANCED BY MIXING THAT TAPS INTO A 40 TO 50 KT
LOW LEVEL JET. GUSTS TO 35 KT FOR THE NEARSHORE WATERS...AND
40-50 KT IN THE OFFSHORE WATERS...COULD BE FREQUENT DURING THIS
TIME. WILL KEEP GALE WARNINGS/STORM WATCH THROUGH WEDNESDAY
AFTERNOON...WITH ONLY THE CHARLESTON HARBOR POSSIBLY DROPPING BACK
TO SMALL CRAFT ADVISORIES IN THE EVENING HOURS.
CONSIDERING THE VERY STRONG OFFSHORE FLOW...WAVE HEIGHTS WILL BE
SOMEWHAT SUPPRESSED. OUTER WATERS WILL LIKELY PEAK AT 10 TO 12 KT
WITHIN THE BETTER FETCH.
GRADUALLY IMPROVING CONDITIONS ARE EXPECTED ON THURSDAY AS THE
PRESSURE GRADIENT WEAKENS WITHIN BUILDING HIGH PRESSURE. ADVISORIES
SHOULD DROP OFF BY THURSDAY AFTERNOON.
LOW PRESSURE WILL DEVELOP IN THE GULF OF MEXICO AND TRACK ACROSS
CENTRAL FLORIDA ON FRIDAY. AS THE COASTAL WATERS REMAIN IN THE COLD
SECTOR OF THIS SYSTEM...NORTHEAST WINDS COULD INCREASE AGAIN FRIDAY
AND SATURDAY. HOWEVER...WITH THE LOW DISPLACED SO FAR SOUTH...THE
STRENGTH OF THE COLD ADVECTION IS QUESTIONABLE. WILL THUS KEEP WINDS
BELOW ADVISORY CRITERIA THURSDAY THROUGH THE REMAINDER OF THE
FORECAST PERIOD.
TIDES/COASTAL FLOODING
NON-METEOROLOGICAL TIDE PREDICTIONS FOR CHARLESTON HARBOR AND FT.
PULASKI ARE 0.4 MLLW AND 0.5 FT MLLW FOR THE LOW TIDE LATE WEDNESDAY
MORNING. GALE FORCE OFFSHORE WINDS WILL LIKELY PUSH TIDES MUCH
LOWER AND COULD POTENTIALLY PRODUCE BLOW-OUT CONDITIONS. CURRENT
THINKING IS THAT TIDES COULD DROP AS LOW AS -2.0 TO -2.5 FT MLLW
WHICH MAY CAUSE SOME NAVIGATION PROBLEMS TO DEVELOP OUTSIDE OF THE
VARIOUS CHANNELS UP AND DOWN THE COAST. WE PLAN TO ADDRESS THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...HIGH WIND WATCH FROM 9 PM EST THIS EVENING THROUGH WEDNESDAY
MORNING FOR SCZ045.
MARINE...GALE WARNING FROM 9 PM THIS EVENING TO 11 PM EST WEDNESDAY FOR
AMZ352-354.
GALE WARNING FROM 9 PM THIS EVENING TO 5 AM EST THURSDAY FOR
AMZ350.
STORM WATCH FROM 9 PM EST THIS EVENING THROUGH WEDNESDAY
MORNING FOR AMZ374.
GALE WARNING FROM 9 PM THIS EVENING TO 5 PM EST WEDNESDAY FOR
AMZ330.
JRL
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