Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
530 FXUS62 KCHS 211815 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 215 PM EDT Fri Aug 21 2026 .WHAT HAS CHANGED... Aviation section updated to represent the 12Z TAF. && .KEY MESSAGES... - 1) Hot and humid conditions will persist today. - 2) Strong to severe thunderstorms possible this afternoon. An increased risk for showers and thunderstorms will continue through Saturday. && .DISCUSSION... KEY MESSAGE 1: Hot and humid conditions will persist today. Rest of Today: The clouds over the region have thrown a wrench into today`s temperature forecast. The updated forecast knocked high temperatures down a degree or two due to the lingering high clouds keeping most location in the upper 80s/low 90s as of noontime. If the sun is able to poke through conditions will likely shoot up quickly, albeit probably briefly, into the mid 90s. Given the persistent cloud cover across southeastern GA the Heat Advisory has been canceled for those counties. The Heat Advisory remains in effect for SC coastal counties through 8 PM this evening, although heat index values will likely only touch the 108 threshold for a short period of time. Saturday will be another hot and humid day, but should be more typical of late August with high temperatures only a degree or two above normal in the low to mid 90s. Dewpoints will remain elevated in the mid to upper 70s along the coast, and the result is expected to be heat indices more commonly in the 100-105 degree range across the forecast area. There could be a small area along the immediate coast that could briefly rise to around 108 degrees, but at this time we do not anticipate sufficient areal or temporal coverage to warrant any Heat Advisories. KEY MESSAGE 2: Strong to severe thunderstorms possible this afternoon. An increased risk for showers and thunderstorms will continue through Saturday. Rest of Today: The ridging aloft that has been driving the hot and humid conditions this last week has been replaced by troughing along the east coast. A shortwave trough will ripple across the southern periphery of the large scale troughing this afternoon and into tonight. At the surface a cold front will approach the region from the W/NW. Scattered to widespread convection is expected this afternoon as the nearby front aids the sea breeze as an extra forcing mechanism. CAMs are not in great agreement with the overall picture of this afternoon and the current forecast features the pure NBM as it appears to be a good middle ground amongst the suite of guidance. Isolated convection is forecast to fire along the sea breeze this afternoon with additional storms forming upstream across the SC Upstate/SC Midlands. These additional storms will then progress towards the local forecast area around sunset this evening. Given the hot and humid airmass strong to severe thunderstorms are possible with any storm that is able to form. SPC Mesoanalysis shows that there is roughly 1500 J/kg of ML CAPE across the forecast area as of noon. This is forecast to increase to around 2000 J/kg by this afternoon. DCAPE values are also forecast to reach upwards of 1000 J/kg. Therefore, damaging wind gusts are the main hazards with any strong/severe storm. Additionally, there is a threat of heavy rainfall with any storm as storm motion will be slow. The 12Z KCHS RAOB sounding had a PWAT of 2.19", which is above the 90th percentile according to SPC Climatology. The boundary from Friday should be positioned nearly right across the forecast area to begin Saturday. The biggest change should come in the depth of available moisture as drier mid and upper level air begins to infiltrate from the west throughout the day. In fact, some model guidance suggests that precipitable water values will fall to less than 1.5 inches across our far inland tier of counties while values up to 2 inches persist along the coastal corridor. There is decent agreement among the hi-res models and the HREF that the best convective coverage should occur along and east of I-95 with development beginning by around midday. Model soundings aren`t don`t suggest a particularly high severe weather threat, but there could still be an isolated strong to marginally severe storm where boundary interactions enhance updraft strength. Instead, there could be more a locally heavy rainfall threat, primarily from the Charleston metro area and to the northeast. Sunday Onward: The aforementioned drier air should spread across the area Sunday into Monday and yield little to no convection at all. However, this should begin to recover starting Tuesday and into the middle of the week with a return to more typical diurnal convective coverage. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... A rather low confidence forecast with the 18Z TAFs at KCHS/KJZI/KSAV. Model guidance this morning has not painted a consistent picture of how the afternoon convection will pan out, which will likely mean additional amendments in the TAFs will be necessary as conditions evolve. The 18Z TAFs feature a TEMPO group for TSRA from 22 to 01Z at KCHS and 23 to 02Z at KSAV. KJZI mentions VCTS. Once the afternoon convection clears there is some indication that some lingering showers could impact KCHS/KJZI, which has been highlighted in a PROB30 from 05 to 08Z. Thereafter, prevailing VFR. Extended Aviation Outlook: Thunderstorms will again be a concern Saturday afternoon and evening. Otherwise, VFR conditions will prevail. && .MARINE... Rest of Today: No significant marine concerns are expected across the local waters through today, with winds and seas remaining below Small Craft Advisory criteria. A typical summertime pattern will dominate with generally south- southwesterly flow around 10 kt and seas 2-3 ft. Saturday through Wednesday: Saturday could bring a period of modestly stronger southwest flow late in the day and into the evening, though wind speeds should top out in the 15-20 knot range. Perhaps the main concern for Saturday will be thunderstorms which are expected to develop along the coast and move out into the coastal waters, potentially producing strong wind gusts and frequent lightning. Thereafter, conditions look pretty typical of summer and should remain well below Small Craft Advisory thresholds through mid week. && .CLIMATE... Record High Minimum Temperatures: August 21: KCHS: 79/2010 KCXM: 82/2023 KSAV: 80/1902 August 24: KCHS: 76/2010 August 25: KCHS: 77/1982 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Heat Advisory until 8 PM EDT this evening for SCZ148>152. MARINE...None. && $$ BSH/CPM