025
FXUS62 KCHS 031534
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1134 AM EDT MON AUG 3 2020
SYNOPSIS
ISAIAS WILL BRING SIGNIFICANT IMPACTS TO OUR AREA THROUGH
TONIGHT. AFTER THE STORM MOVES AWAY, A STATIONARY FRONT WILL
THEN HOVER OVER OR NEAR THE AREA MID TO LATE IN THE WEEK.
NEAR TERM /THROUGH TONIGHT/
LATE THIS MORNING: THE CIRCULATION OF TROPICAL STORM ISAIAS
CONTINUES TO MOVE NORTHWARD TOWARD THE SOUTHEAST SOUTH CAROLINA
COAST AND THE PRECIPITATION SHIELD ASSOCIATED WITH IT IS ALSO
EXPANDING NORTHWARD. THE OFFICIAL NHC TRACK FORECAST HAS TRENDED
A BIT TO THE EAST IN THE LAST FEW ADVISORIES, AS WELL AS A BIT
FASTER. THIS WILL HAVE NOTABLE IMPLICATIONS FOR RAINFALL AND
STORM SURGE RELATED IMPACTS. OVERALL THE WIND FORECAST HAS NOT
CHANGED SIGNIFICANTLY AS THE SLIGHTLY MORE OFFSHORE FORECAST IS
BALANCED A BIT BY THE FORECAST STRENGTHENING TO A HURRICANE IN
THE NEXT 6-12 HOURS. STRONGEST WINDS ARE STILL EXPECTED TO
IMPACT THE AREA FROM BEAUFORT COUNTY UP THROUGH THE TRI-COUNTY
REGION, PRIMARILY IN LOCATIONS CLOSER TO THE COAST.
RAINFALL REMAINS A RATHER CHALLENGING FORECAST. THERE WILL BE A
VERY TIGHT GRADIENT ON THE WEST SIDE OF THE PRECIPITATION
SHIELD, MEANING THAT OVER A SHORT DISTANCE WE WILL GO FROM
RATHER LIGHT RAINFALL AMOUNTS TO RATHER SIGNIFICANT RAINFALL
AMOUNTS THAT COULD RESULT IN FLOODING IMPACTS. BASED ON THE
SUITE OF MODELS AND THE OFFICIAL TRACK FORECAST, WE STILL LOOK
ON TRACK TO HAVE THE HIGHEST AMOUNTS OCCUR ACROSS THE CHARLESTON
TRI-COUNTY REGION. EXPECTED AMOUNTS HAVEN'T CHANGED AT THIS
POINT, WITH 3-6 INCHES WITH LOCALLY HIGHER AMOUNTS WHERE THE
FLASH FLOOD WATCH IS IN PLACE. WEST OF THIS (AND GENERALLY WEST
OF THE I-95 CORRIDOR) AMOUNTS ARE STILL MUCH LESS, WITH MUCH OF
SOUTHEAST GEORGIA WELL LESS THAN AN INCH. THE FLASH FLOOD WATCH
STILL HIGHLIGHTS THE AREA OF HEAVIEST RAIN, AND REMAINS IN
PLACE. THE LATE AFTERNOON INTO THE EVENING TIME PERIOD IS STILL
THE PERIOD OF GREATEST CONCERN. ONE BIT OF GOOD NEWS IS THAT
BASED ON THE CURRENT FORWARD SPEED OF THE STORM, WE MIGHT AVOID
SEEING THE PEAK SURGE PERFECTLY COINCIDE WITH HIGH TIDE. THIS
WOULD LESSEN THE PEAK MAGNITUDE OF POTENTIAL FLOODING, BUT TIDE
LEVELS WILL STILL BE ELEVATED WITH HEAVY RAIN SO AT LEAST SOME
FLOODING IS EXPECTED IN AND AROUND DOWNTOWN CHARLESTON.
WE CONTINUE TO MONITOR THE TORNADO THREAT, BUT IT REMAINS
LIMITED TO COASTAL AREAS IN AND AROUND THE TRI-COUNTY REGION.
THE LACK OF INSTABILITY AND SLIGHTLY MORE EASTWARD TRACK SHOULD
KEEP THE MAIN THREAT ZONE OVER THE COASTAL WATERS, BUT WE COULD
STILL SEE ROTATING STORMS APPROACH AND PERHAPS MOVE INTO THE
COAST.
CONDITIONS WILL QUICKLY IMPROVE FROM SOUTH TO NORTH TONIGHT AS
ISAIAS MOVES AWAY TO THE NORTH WITH THE RAIN ENDING AND WIND
SUBSIDING. LOWS TONIGHT SHOULD MAINLY BE IN THE LOWER TO MID
70S.
SHORT TERM /TUESDAY THROUGH THURSDAY/
TUESDAY: ISAIAS WILL BE FAR TO THE NORTH OF OUR AREA IN THE
MORNING AND CONTINUING TO QUICKLY MOVE AWAY AS IT GETS ABSORBED
INTO A MID- LEVEL TROUGH ALONG THE EAST COAST. MEANWHILE,
RELATIVELY DRIER AIR BE IN PLACE ACROSS OUR AREA IN THE MORNING.
THOUGH, A COLD FRONT SHOULD APPROACH OUR AREA FROM THE WEST IN
THE AFTERNOON, THEN TRANSITION TO A STATIONARY FRONT DURING THE
EVENING AND OVERNIGHT HOURS. MODELS INDICATE SOME SEA BREEZE
CONVECTION FORMING IN THE AFTERNOON, WITH THE HIGHEST
PROBABILITIES ACROSS OUR GA COUNTIES. THERE DOESN'T APPEAR TO BE
MUCH INSTABILITY IN PLACE, SO THE SEVERE RISK IS LOW. THE
CONVECTION SHOULD DISSIPATE IN THE EVENING, THEN TRANSITION TO
THE COASTAL WATERS OVERNIGHT. AFTERNOON TEMPERATURES SHOULD PEAK
IN THE 90S WHILE OVERNIGHT LOWS WILL GENERALLY BE IN THE 70S.
WEDNESDAY AND THURSDAY: A MID-LEVEL TROUGH WILL STRETCH FROM
THE GREAT LAKES REGION DOWN INTO THE DEEP SOUTH. MEANWHILE, A
STATIONARY FRONT WILL GENERALLY BE JUST WEST OF OUR AREA. MODELS
ARE IN GOOD AGREEMENT SHOWING A RETURN TO OUR TYPICAL
SUMMERTIME PATTERN. HIGH TEMPERATURES SHOULD BE IN THE LOW TO
MID 90S. INSTABILITY AND LIFT FROM THE AFTERNOON SEA BREEZE ARE
EXPECTED TO FIRE OFF SHOWERS/THUNDERSTORMS. THOUGH, THE DETAILS
WILL NEED TO BE REFINED AS THIS TIME PERIOD GETS CLOSER. SOME
CONVECTION COULD PERSIST INTO THE OVERNIGHT HOURS. LOWS ARE
FORECASTED TO BE IN THE 70S.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
A MID-LEVEL TROUGH WILL PERSIST OVER THE EAST COAST WHILE A
STATIONARY FRONT HOVERS OVER OR NEAR AREA. THE TYPICAL AFTERNOON
AND EVENING SHOWERS AND THUNDERSTORMS ARE EXPECTED.
TEMPERATURES SHOULD BE NEAR NORMAL.
AVIATION /15Z MONDAY THROUGH FRIDAY/
CONDITIONS ARE EXPECTED TO CONTINUE TO DETERIORATE TO AT LEAST
MVFR BUT LIKELY IFR OR WORSE AT TIMES AS BANDS OF SQUALLY
SHOWERS AND ISOLATED STORMS SHIFT WEST THROUGH THE AREA AHEAD OF
ISAIAS. WINDS WILL ALSO STEADILY INCREASE EVEN OUTSIDE OF THE
RAIN AS ISAIAS NEARS THE AREA FROM THE SOUTHEAST WITH GUSTS UP
TO 20-25 KT AT KSAV THROUGH ABOUT 00Z TUESDAY AND GUSTS TO
AROUND 40 KT AT KCHS FROM AROUND 21Z MONDAY THROUGH ABOUT 03Z
TUESDAY. STRONGER WINDS GUSTS WILL BE POSSIBLE HOWEVER IN THE
HEAVIEST SHOWERS/STORMS. CONDITIONS COULD IMPROVE TO VFR LATE IN
THE 06Z TAF PERIOD AT KSAV.
EXTENDED AVIATION OUTLOOK: BRIEF FLIGHT RESTRICTIONS ARE
POSSIBLE WITHIN SHOWERS/THUNDERSTORMS, MAINLY EACH AFTERNOON
THROUGH FRIDAY.
MARINE
TODAY AND TONIGHT: TROPICAL STORM ISAIAS WILL MOVE NORTH
THROUGH THE LOCAL WATERS BRINGING DANGEROUS MARINE CONDITIONS,
WHILE POSSIBLY STRENGTHENING TO A MINIMAL HURRICANE. TROPICAL
STORM WARNINGS REMAIN IN EFFECT FOR THE ENTIRE AREA INCLUDING
THE CHARLESTON HARBOR, ALTHOUGH HURRICANE WARNINGS COULD BE
NEEDED, ESPECIALLY FOR THE OFFSHORE GA WATERS AND CHARLESTON
COUNTY NEARSHORE WATERS. CONDITIONS WILL ALSO BE FAVORABLE FOR
WATERSPOUTS ESPECIALLY FROM LATE MORNING THROUGH EARLY EVENING.
EXPECT QUICKLY IMPROVING CONDITIONS FROM SOUTH TO NORTH TONIGHT
AS ISAIAS MOVES AWAY TO THE NORTH. WE COULD NEED SMALL CRAFT
ADVISORIES IN THE IMMEDIATE WAKE TO AT LEAST ACCOUNT FOR
RESIDUAL ELEVATED SEAS.
TUESDAY THROUGH SATURDAY: ANY MARINE HEADLINES IN EFFECT
TUESDAY MORNING SHOULD BE DUE TO ELEVATED SEAS FROM THE STORM.
THOUGH, THEY WILL QUICKLY SUBSIDE INTO TUESDAY AFTERNOON AS THE
STORM MOVES AWAY. A STATIONARY FRONT IS THEN FORECASTED TO STAY
ALONG THE SOUTHEAST COAST MID TO LATE THIS WEEK, LEADING TO A
RETURN OF THE TYPICAL SUMMER CONDITIONS. WINDS AND SEAS ARE
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA DURING
THIS TIME PERIOD.
RIP CURRENTS: DANGEROUS SURF CONDITIONS ARE EXPECTED THROUGH
TONIGHT AS ISAIAS MOVES NORTH JUST OFF THE SOUTHEAST GEORGIA AND
SOUTHEAST SOUTH CAROLINA COASTS. NOBODY SHOULD ENTER THE WATER
DURING THIS TIME.
ON TUESDAY, REMNANT SWELL FROM THE DEPARTING STORM WILL BE
MOVING THROUGH THE COASTAL WATERS. THE COMBINATION OF THIS
SWELL, WINDS GRADUALLY TURNING ONSHORE, AND NEW COASTAL
BATHYMETRY IN SOME AREAS POST STORM WILL MAKE IT EASY FOR RIP
CURRENTS TO FORM. A MODERATE RISK IS NOW IN EFFECT.
HYDROLOGY
PERIODS OF HEAVY RAINFALL ARE EXPECTED TODAY AS OUTER BANDS OF
ISAIAS MOVE INLAND ACROSS THE AREA. MORE STEADY HEAVIER RAIN IS
THEN LIKELY TO PUSH INTO THE SC COAST LATER TODAY INTO THIS
EVENING AND THE HIGHEST TOTAL RAINFALL AMOUNTS ARE EXPECTED
GENERALLY AROUND THE CHARLESTON METRO WHERE 6 OR MORE INCHES
COULD FALL. OUR BIGGEST CONCERN IS THE THREAT FOR HEAVY RAIN
DURING THE EVENING HIGH TIDE WHICH COULD CAUSE SIGNIFICANT
FLOODING IN AREAS LIKE DOWNTOWN CHARLESTON DUE TO THE
COMBINATION OF FRESHWATER AND TIDAL FLOODING.
TIDES/COASTAL FLOODING
WITH A FORECAST OF STORM SURGE INUNDATION IN THE 2-4 FT RANGE,
A STORM SURGE WARNING REMAINS UP FROM EDISTO BEACH NORTH THROUGH
THE SOUTH SANTEE RIVER. THE BEST CHANCE OF SEEING THE PEAK
INUNDATION OF 4 FEET WILL BE IF ISAIAS MAKES LANDFALL IN OUR
FORECAST AREA, MAINLY IN AREAS JUST TO THE RIGHT/NORTH OF
LANDFALL. WHERE THE SS WARNING IS IN PLACE, NO COASTAL FLOOD
ADVISORIES/WARNINGS WILL BE ISSUED, ALTHOUGH SOUTH OF THE STORM
SURGE WARNING AREA WE WILL ISSUE THOSE PRODUCTS AS NEEDED.
HOWEVER, AT THIS TIME WE DO NOT ANTICIPATE REACHING MAJOR
COASTAL FLOOD THRESHOLDS SOUTH OF EDISTO BEACH SO A COASTAL
FLOOD WARNING IS UNLIKELY. HOWEVER, THIS COULD CHANGE IF ISAIAS
ENDS UP BEING SLOWER TO ARRIVE AND/OR STRONGER ALLOWING THE PEAK
SURGE TO BETTER ALIGN WITH THE HIGH TIDE.
CLIMATE
DAILY RAINFALL RECORDS FOR AUGUST 3...
KCHS: 4.60 INCHES
KCXM: 2.60 INCHES
KSAV: 4.17 INCHES
CHS WATCHES/WARNINGS/ADVISORIES
GA...TROPICAL STORM WARNING FOR GAZ116>119-138>141.
HIGH RISK FOR RIP CURRENTS UNTIL 8 PM EDT THIS EVENING FOR GAZ117-
119-139-141.
HIGH SURF ADVISORY UNTIL 2 AM EDT TUESDAY FOR GAZ117-119-139-
141.
WIND ADVISORY UNTIL 2 AM EDT TUESDAY FOR GAZ101.
SC...TROPICAL STORM WARNING FOR SCZ044-045-047>052.
HIGH RISK FOR RIP CURRENTS UNTIL 8 PM EDT THIS EVENING FOR
SCZ048>051.
HIGH SURF ADVISORY UNTIL 2 AM EDT TUESDAY FOR SCZ048-051.
FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR SCZ044-045-048>050-
052.
WIND ADVISORY UNTIL 2 AM EDT TUESDAY FOR SCZ042-043.
STORM SURGE WARNING FOR SCZ049-050.
HIGH SURF ADVISORY UNTIL 8 AM EDT TUESDAY FOR SCZ049-050.
MARINE...TROPICAL STORM WARNING FOR AMZ330-350-352-354-374.
NEAR TERM...BSH/RJB
SHORT TERM...MS
LONG TERM...MS
AVIATION...RJB/MS
MARINE...RJB/MS
HYDROLOGY...
TIDES/COASTAL FLOODING...
CLIMATE...
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page