444
FXUS62 KCHS 181827
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
227 PM EDT TUE AUG 18 2026
WHAT HAS CHANGED
ALL SECTIONS HAVE BEEN UPDATED.
KEY MESSAGES
- 1) HEAT WILL REMAIN A CONCERN INTO LATE WEEK.
- 2) AFTERNOON AND EVENING THUNDERSTORM COVERAGE WILL REMAIN
ISOLATED THROUGH THURSDAY. AN INCREASE IN THUNDERSTORM
COVERAGE IS EXPECTED FRIDAY THROUGH THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: HEAT WILL REMAIN A CONCERN TODAY LATE WEEK.
REST OF TODAY: STRONG RIDGING ALOFT WILL REMAIN THE MAIN
SYNOPTIC FEATURE INFLUENCING THE LOCAL FORECAST AREA TODAY. AT
THE SURFACE VERY WEAK TROUGHING IS IN PLACE ALONG THE COASTLINE.
THE RIDGING ALOFT HAS LED TO A NORTHWESTERLY FLOW TODAY,
PINNING THE SEA BREEZE TO THE COASTLINE. THE DELAYED INLAND
PROGRESSION OF THE SEA BREEZE WILL ALLOW TEMPERATURES THIS
AFTERNOON TO SOAR INTO THE UPPER 90S ACROSS MOST LOCATIONS, WITH
A FEW SPOTS TOUCHING 100. THIS NORTHWESTERLY FLOW WILL ALLOW
FOR SOME MIXING OF TDS ACROSS THE REGION, HOWEVER ONCE THE SEA
BREEZE DOES PUSH INLAND TD VALUES ARE EXPECTED TO REACH INTO THE
MID TO UPPER 70S ACROSS COASTAL LOCATIONS. HEAT INDEX VALUES OF
UP TO 106-112 ARE FORECAST INLAND AND 113-119 IS FORECAST
ACROSS THE COASTAL CORRIDOR. ADDITIONALLY, LIMITED CONVECTION
THIS AFTERNOON WILL PROVIDE LITTLE RELIEF FROM THE HEAT. AN
EXTREME HEAT WARNING REMAINS IN EFFECT FROM 11 AM TO 8 PM TODAY
FOR SC/GA COASTAL COUNTIES AND ALSO INCLUDES DORCHESTER COUNTY,
SC AND EFFINGHAM COUNTY, GA. A HEAT ADVISORY REMAINS IN EFFECT
FROM 11 AM TO 8 PM TODAY FOR ALL REMAINING INLAND AREAS AS WELL.
WEDNESDAY INTO FRIDAY: THE RIDGING ALOFT WILL BEGIN TO WEAKEN
SLOWLY STARTING ON WEDNESDAY. THIS WILL ALLOW FOR CONVECTION TO
INCREASE IN COVERAGE EACH AFTERNOON. HEAT INDEX VALUES ARE STILL
FORECAST TO REACH HEAT ADVISORY CRITERIA (>108) ALONG THE
COASTAL CORRIDOR WHERE DEW POINTS WILL BE HIGHEST. A HEAT
ADVISORY HAS BEEN ISSUED FROM 11 AM TO 8 PM WEDNESDAY FOR THE
COASTAL COUNTIES. ADDITIONAL HEAT ADVISORIES WILL LIKELY BE
REQUIRED THURSDAY AND POSSIBLY AGAIN ON FRIDAY. CONVECTIVE
COVERAGE WILL INCREASE INTO FRIDAY AS A SHORTWAVE TROUGH ALOFT
MOVES THROUGH THE MID-ATLANTIC STATES. FRIDAY COULD SEE THE
GREATEST COVERAGE OF SHOWERS AND THUNDERSTORMS, POSSIBLY
HINDERING TEMPERATURES FROM REACHING THEIR PEAK VALUES AND
NEGATING THE NEED FOR ANY HEAT HEADLINES.
KEY MESSAGE 2: AFTERNOON AND EVENING THUNDERSTORM COVERAGE WILL
REMAIN ISOLATED THROUGH THURSDAY. AN INCREASE IN THUNDERSTORM
COVERAGE IS EXPECTED FRIDAY THROUGH THE WEEKEND.
THIS AFTERNOON AND EVENING: THE BACKGROUND SYNOPTIC-SCALE SETUP
FEATURES A FRONT THAT MOSTLY STRETCHES FROM WEST TO EAST
SITUATED NORTH OF THE FORECAST AREA. THIS IS DRIVING WEST TO
WEST-NORTHWEST SURFACE FLOW ACROSS THE AREA, WHICH WILL FORCE
THE SEA BREEZE TO BE LATE DEVELOPING AND PINNED VERY CLOSE TO
THE COAST. GIVEN THAT WE ARE DEVOID OF ANY FORCING MECHANISM FOR
CONVECTION OTHER THAN DIFFERENTIAL SURFACE HEATING AND THE SEA
BREEZE, THE ENVIRONMENT DOESN'T SUPPORT MUCH IN THE WAY OF
COVERAGE. THIS IS WELL SUPPORTED BY THE HI-RES MODEL RUNS AS
WELL AS THE 18/12Z HREF, ALL OF WHICH SHOW LITTLE TO DIURNAL
CONVECTION. BUT, IF A STORM OR TWO CAN GET GOING THERE WILL BE A
LOW RISK OF A STRONG TO MARGINALLY SEVERE STORM.
WEDNESDAY AND THURSDAY: A SIMILAR ENVIRONMENT IS EXPECTED EACH
DAY FAVORING ISOLATED TO SCATTERED CONVECTIVE COVERAGE AT MOST.
WE WILL STILL BE DETACHED FROM ANY MEANINGFUL FORCING SO WE WILL
CONTINUE TO BE DEPENDENT ON SURFACE HEATING AND CONVERGENCE
ALONG THE SEA BREEZE. THE TYPICAL SUMMERTIME RULES APPLY IN THAT
ANY STORM THAT DEVELOPS COULD BECOME MARGINALLY SEVERE, PRODUCE
LOCALLY HEAVY RAINFALL, AND ALSO FREQUENT LIGHTNING.
FRIDAY THROUGH THE WEEKEND: THE EXPECTATION REMAINS THAT THE
PATTERN WILL BECOME MORE ACTIVE AS WE MOVE INTO THE WEEKEND. A
SLOW MOVING FRONT IS EXPECTED TO SETTLE INTO THE AREA AND HELP
PROVIDE MORE OF A TRIGGERING AND FOCUSING MECHANISM FOR
THUNDERSTORM DEVELOPMENT. WITH CONTINUED ELEVATED PRECIPITABLE
WATER VALUES, THIS INCREASE IN COVERAGE SHOULD BRING THE
POTENTIAL FOR LOCALLY HEAVY RAINFALL AND SEVERAL ROUNDS OF
THUNDERSTORMS ACROSS THE FORECAST AREA EACH DAY.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
THE 18Z TAF PERIOD BEGINS WITH VFR CONDITIONS AT KCHS, KJZI,
AND KSAV. OVERALL, VFR CONDITIONS ARE EXPECTED TO PREVAIL
THROUGH 18Z WEDNESDAY. THE ONLY SMALL CONCERN IS THE LOW CHANCE
THAT A SHOWER OR THUNDERSTORM COULD DEVELOP THIS AFTERNOON OR
EVENING, PRIMARILY NEAR KSAV. HOWEVER, THE OVERALL LIKELIHOOD
APPEARS QUITE LOW AND WE WILL NOT INCLUDE ANY EXPLICIT MENTION
IN THE TAF.
EXTENDED AVIATION OUTLOOK: PREVAILING VFR THROUGH THURSDAY.
AFTERNOON SHOWERS AND THUNDERSTORMS COULD BRING BRIEF FLIGHT
RESTRICTIONS STARTING FRIDAY.
MARINE
THROUGH TONIGHT: WEST WINDS WILL CONTINUE UNTIL THE LATE
DEVELOPING SEA BREEZE GETS GOING. SOUTHWEST FLOW WILL PREVAIL
THIS EVENING, TURNING MORE WESTERLY THROUGH THE LATE NIGHT
HOURS. WINDS SHOULD MOSTLY TOP OUT IN THE 10-15 KNOT RANGE THIS
EVENING, DIMINISHING MORE TO BE 5-10 KNOTS LATE TONIGHT. SEAS
ARE EXPECTED TO AVERAGE 2-3 FEET.
WEDNESDAY THROUGH SUNDAY: OVERALL, A PRETTY TYPICAL SUMMERTIME
PATTERN IS EXPECTED TO PREVAIL ACROSS THE LOCAL WATERS THROUGH
THE WEEKEND. WINDS WILL LOCALLY SURGE WITH THE SEA BREEZE EACH
DAY, MOSTLY INTO THE 10-15 KNOT RANGE AND PERHAPS A FEW GUSTS UP
TO 20 KNOTS. OVER THE WEEKEND THERE COULD BE SOME SUPPORT FOR
MORE 15-20 KNOT SOUTHWEST FLOW THANKS TO A BIT MORE GRADIENT.
BUT, OVERALL CONDITIONS ACROSS THE LOCAL WATERS SHOULD REMAIN
BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH THE PERIOD.
CLIMATE
RECORD HIGH TEMPERATURES:
AUGUST 18:
KCHS: 101/1995
KCXM: 97/1995
KSAV: 100/1995
AUGUST 19:
KCHS: 98/1983
KCXM: 98/1895
KSAV: 99/1900
AUGUST 20:
KCHS: 97/2005
KSAV: 102/1900
AUGUST 21:
KCHS: 100/1983
KSAV: 101/1902
RECORD HIGH MINIMUM TEMPERATURES:
AUGUST 18:
KCHS: 80/2017
KCXM: 82/2017
KSAV: 78/2010
AUGUST 19:
KCHS: 79/2010
KCXM: 83/2021
KSAV: 79/1878
AUGUST 20:
KCHS: 78/2017
KCXM: 82/2017
AUGUST 21:
KCHS: 79/2010
KCXM: 82/2023
KSAV: 80/1902
AUGUST 22:
KCHS: 79/2023
KCXM: 82/2014
KSAV: 79/1902
AUGUST 23:
KCXM: 81/2019
KSAV: 78/2016
CHS WATCHES/WARNINGS/ADVISORIES
GA...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ087-088-099-
100-114-115-137.
EXTREME HEAT WARNING UNTIL 8 PM EDT THIS EVENING FOR GAZ101-
216>219-238>241.
HEAT ADVISORY FROM 11 AM TO 8 PM EDT WEDNESDAY FOR GAZ217>219-
239>241.
SC...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ040-042-043.
EXTREME HEAT WARNING UNTIL 8 PM EDT THIS EVENING FOR SCZ044-
045-147>152.
HEAT ADVISORY FROM 11 AM TO 8 PM EDT WEDNESDAY FOR SCZ148>152.
MARINE...NONE.
BSH/CPM
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