823
FXUS62 KCHS 201810
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
210 PM EDT THU AUG 20 2026
WHAT HAS CHANGED
ALL SECTIONS UPDATED.
KEY MESSAGES
- 1) DANGEROUS HEAT WILL REMAIN A CONCERN TODAY AND TOMORROW.
- 2) ISOLATED SHOWERS AND THUNDERSTORMS EXPECTED THIS AFTERNOON,
BEFORE INCREASING IN COVERAGE ON FRIDAY THROUGH THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: DANGEROUS HEAT WILL REMAIN A CONCERN TODAY AND
TOMORROW.
REST OF TODAY: STRONG RIDGING ALOFT WILL REMAIN THE MAIN SYNOPTIC
FEATURE INFLUENCING THE LOCAL FORECAST AREA TODAY. A HEAT ADVISORY
REMAINS IN PLACE FOR THE COASTAL COUNTIES AND BERKELEY COUNTY
THROUGH 8 PM THIS EVENING. HEAT INDEX VALUES WITHIN THE HEAT
ADVISORY AREA COULD REACH AS HIGH AS 110. CONVECTION THIS AFTERNOON
ACROSS THE CHARLESTON TRI-COUNTY WILL PROVIDE SOME RELIEF FROM THE
HEAT TO A FEW LOCATIONS.
FRIDAY: MID-LEVEL TROUGHING WILL DOMINATE THE EAST COAST WHILE A
WEAK SURFACE FRONT APPROACHES THE LOCAL FORECAST AREA. TEMPERATURES
ARE STILL FORECAST TO BE ABOVE NORMAL (MID 90S), BUT HEAT INDEX
VALUES LOOK TO FALL SHORT OF HEAT ADVISORY CRITERIA ACROSS MOST OF
THE REGION. THE ONLY LOCATIONS THAT COULD SEE HEAT INDEX VALUES OF
108 OR GREATER WOULD BE ALONG THE COASTAL COUNTIES, ESPECIALLY IN
SC. HOWEVER, GIVEN THE INCREASED COVERAGE OF PRECIPITATION THERE IS
LITTLE CONFIDENCE IN HITTING THE HEAT ADVISORY CRITERIA. THEREFORE,
ONE HAS NOT BEEN ISSUED AT THIS JUNCTURE.
THIS WEEKEND INTO EARLY NEXT WEEK: TEMPERATURES WILL COOL SLIGHTLY,
WITH HIGHS IN THE LOW 90S (STILL ABOVE NORMAL FOR THIS TIME OF
YEAR). THE EXTENDED FORECAST LOOKS TO BE HEAT-HEADLINE FREE WITH
HEAT INDEX VALUES TOPPING OUT IN THE 100-103 RANGE EACH
AFTERNOON.
KEY MESSAGE 2: ISOLATED SHOWERS AND THUNDERSTORMS EXPECTED THIS
AFTERNOON, BEFORE INCREASING IN COVERAGE ON FRIDAY THROUGH THE
WEEKEND.
THIS AFTERNOON: AS MID-LVL RIDGING REMAINS STATIONED ACROSS THE
REGION, A WEAK COASTAL TROUGH + THE AFTERNOON SEA BREEZE WILL YIELD
ISOLATED SHOWERS AND THUNDERSTORMS THIS AFTERNOON. THE LATEST
HRRR/CAM GUIDANCE CONTINUES TO INDICATE THAT THE MAJORITY OF
CONVECTION WILL REMAIN ACROSS THE CHARLESTON TRI-COUNTY. INITIAL
DEVELOPMENT WILL LIKELY DEVELOP ALONG THE AFTERNOON SEA BREEZE,
BEFORE PUSHING INLAND WHERE THE SEA BREEZE WILL INTERACT WITH PRE-
EXISTING BOUNDARIES. SBCAPE VALUES OF ROUGHLY 2000-3000 J/KG, WITH
LOCALLY HIGHER VALUES, IS EXPECTED BY PEAK HEATING, WHILE SBCAPE
VALUES SHOULD EXCEED 1000 J/KG. THEREFORE, ANY STORM THAT DOES
BECOME ESTABLISHED COULD QUICKLY BECOME STRONG, WITH LOCALIZED
DAMAGING WIND GUSTS AS THE PRIMARY CONCERN. DEEP-LAYER SHEAR REMAINS
RATHER WEAK, SO ORGANIZED AND/OR LONG-LIVED SEVERE CONVECTION DOES
NOT APPEAR TO BE IN THE CARDS THIS AFTERNOON. INSTEAD, THE THREAT
SHOULD CONSIST OF PULSE-TYPE STORMS AND LOOSELY ORGANIZED MULTICELL
CLUSTERS. COVERAGE ACROSS SOUTHEAST GEORGIA APPEARS MORE ISOLATED
AND WILL BE DEPENDENT UPON OUTFLOW BOUNDARIES PROPAGATING
SOUTH/SOUTHWEST FROM EARLIER CONVECTION. ALSO, HEAVY RAINFALL WILL
BE A CONCERN AS WELL WITH ANY SLOW-MOVING STORM WITH PWATS RANGING
FROM 1.8 TO 2.0 INCHES AND WEAK STEERING FLOW PRESENT. WHILE
WIDESPREAD FLOODING IS NOT EXPECTED, RAINFALL AMOUNTS OF A COUPLE
INCHES COULD OCCUR BENEATH THE STRONGER STORMS, YIELDING LOCALIZED
FLOODING OF POOR-DRAINAGE LOCATIONS. OVERALL, CONVECTION THIS
AFTERNOON SHOULD BE MORE LOCALIZED THAN THE NEXT UPCOMING DAYS.
FRIDAY: A MORE APPRECIABLE CHANGE IN THE PATTERN IS EXPECTED ON
FRIDAY AS THIS MID-LVL RIDGE FINALLY BREAKS DOWN AND BROAD TROUGHING
BEGINS TO BUILD ACROSS THE EASTERN HALF OF THE CONUS. SEVERAL
EMBEDDED SHORTWAVES ARE FORECAST TO ROUND THE BASE OF THIS TROUGH
WHILE A SLOW-MOVING SURFACE FRONT APPROACHES THE REGION FROM THE
WEST AND NORTHWEST. THIS WILL PROVIDE GREATER CONVECTION COVERAGE
THAN THE PREVIOUS DAY (THURSDAY).
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP MID-
DAY/EARLY AFTERNOON, BEFORE BECOMING NUMEROUS AND WIDESPREAD IN THE
AFTERNOON/EVENING HOURS. EXPECT MOISTURE TO INCREASE SUBSTANTIALLY
AHEAD OF THIS APPROACHING FRONT, WITH PWAT VALUES FORECAST TO RISE
ABOVE 2 INCHES (NEAR THE 90TH PERCENTILE FOR LATE AUGUST AT KCHS).
DESPITE SOMEWHAT GREATER CLOUD COVER AND TEMPERATURES SEVERAL
DEGREES LOWER THAN THE PREVIOUS COUPLE DAYS, SUFFICIENT HEATING
SHOULD STILL YIELD MODERATE TO LOCALLY STRONG INSTABILITY. THE
COMBINATION OF INSTABILITY, ABUNDANT MOISTURE, AND APPRECIABLE DCAPE
VALUES WILL SUPPORT ANOTHER RISK FOR STRONG TO SEVERE STORMS. THUS,
THE SPC HAS HIGHLIGHTED THE MAJORITY OF THE REGION IN A MARGINAL
RISK (LEVEL 1/5) FOR SEVERE THUNDERSTORMS ON FRIDAY. AGAIN, DAMAGING
WIND GUSTS WILL BE THE GREATEST THREAT (WITHIN THE STRONGER STORMS),
ALONG WITH LOCALIZED FLOODING POSSIBLE.
SATURDAY: ANOTHER SCATTERED TO NUMEROUS SHOWER AND THUNDERSTORM DAY
AS THE FRONT STALLS NEAR THE REGION. THE EXACT CORRIDOR OF GREATEST
COVERAGE IS LESS CERTAIN AND WILL DEPEND HEAVILY ON THE FRONTAL
POSITION. STRONG WIND GUSTS REMAIN POSSIBLE AGAIN, BUT TRAINING
STORMS AND LOCALIZED FLASH FLOODING COULD BECOME AN INCREASING
CONCERN GIVEN PWATS NEAR 2 INCHES AND STORMS POTENTIALLY TRACKING
PARALLEL TO THE BOUNDARY.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
KCHS/KJZI: A TEMPO GROUP HAS BEEN INTRODUCED FROM 18 TO 21Z THIS
AFTERNOON TO ACCOUNT FOR THE THREAT OF THUNDERSTORMS. THEREAFTER,
PREVAILING VFR THROUGH THE REMAINDER OF THE 18Z TAF PERIOD. THERE IS
A CHANCE THAT SHOWERS/THUNDERSTORMS COULD IMPACT THE TERMINALS CLOSE
TO 18Z ON FRIDAY AFTERNOON, HOWEVER MENTION OF ANY IMPACTS HAS NOT
BEEN INCLUDED WITH THESE 18Z TAFS.
KSAV: PREVAILING VFR THROUGH THE 18Z TAF PERIOD.
EXTENDED AVIATION OUTLOOK: A FRONT IN OUR VICINITY WILL BRING
SHOWERS AND THUNDERSTORMS FRIDAY INTO THE WEEKEND, LEADING TO
OCCASIONAL FLIGHT RESTRICTIONS.
MARINE
REST OF TODAY/TONIGHT: NO SIGNIFICANT MARINE CONCERNS ARE EXPECTED
ACROSS THE LOCAL WATERS THROUGH TONIGHT, WITH WINDS AND SEAS
REMAINING BELOW SMALL CRAFT ADVISORY CRITERIA. A TYPICAL SUMMERTIME
PATTERN WILL DOMINATE, WITH GENERALLY SOUTH-SOUTHWESTERLY FLOW
AROUND 5-10 KT BECOMING MORE SOUTH-SOUTHEASTERLY THIS AFTERNOON AS
THE SEA BREEZE PUSHES INLAND. WINDS COULD BRIEFLY INCREASE TO 10-15
KT ALONG THE IMMEDIATE COASTLINE AND ACROSS THE CHARLESTON HARBOR
LATE THIS AFTERNOON AND EVENING. SEAS SHOULD GENERALLY RANGE FROM 2-
3 FT.
EXTENDED MARINE: OUTSIDE OF SHOWERS AND THUNDERSTORMS, OVERALL
MARINE CONDITIONS WILL REMAIN FAIRLY TYPICAL FOR LATE SUMMER, WITH
SOUTH-SOUTHWESTERLY WINDS GENERALLY 5-15 KT WITH SEAS RANGING FROM 2-
4 FT THROUGH EARLY NEXT WEEK. THE MAIN CONCERN FOR MARINERS WILL BE
THE INCREASING THUNDERSTORM THREAT THROUGH THE WEEKEND AS A FRONT
APPROACHES AND THEN STALLS NEARBY.
CLIMATE
RECORD HIGH TEMPERATURES:
AUGUST 20:
KCHS: 97/2005
KSAV: 102/1900
RECORD HIGH MINIMUM TEMPERATURES:
AUGUST 20:
KCHS: 78/2017
KCXM: 82/2017
AUGUST 21:
KCHS: 79/2010
KCXM: 82/2023
KSAV: 80/1902
AUGUST 22:
KCHS: 79/2023
AUGUST 24:
KCHS: 76/2010
KCXM: 80/1975
AUGUST 25:
KCHS: 77/1982
AUGUST 26:
KCHS: 78/1998
CHS WATCHES/WARNINGS/ADVISORIES
GA...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ217>219-
239>241.
SC...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ045-148>152.
MARINE...NONE.
CPM/DENNIS
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