Area Forecast Discussion
Issued by NWS Charleston, SC

Current Version |  Previous Version |  Text Only |  Print | Product List |  Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
390 FXUS62 KCHS 241707 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 107 PM EDT Tue Jun 24 2025 .SYNOPSIS... High pressure will remain across the Southeast U.S. over the next couple days, then slowly shift offshore by the end of the week. Hot and humid conditions are expected to continue with rain chances increasing mid to late week as surface troughing begins to form over the region. && .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Early this afternoon: No change to the forecast. Previous discussion continues below. Late this morning: The primary forecast issue is the heat. Low- level thickness values from the 12z KCHS RAOB are higher than 24 hours ago as anticipated, and support highs in the upper 90s away from the immediate coast. These temperatures, combined with dewpoints in the upper 60s to low 70s will yield heat index values solidly in the 105-110 degree range across the area. Inland areas will likely see dewpoints mix out a bit more (upper 60s) and in these areas heat indices will likely fall a little short of our explicit Heat Advisory criteria (heat index of 108-112). The areas most likely to exceed 108 heat index are along the coastal corridor where dewpoints will sit a bit higher, and across the entire Charleston Tri-County region. Regardless of specific heat index criteria, it will be quite hot and humid and supportive of the Heat Advisory that is already in place. The other forecast issue of the day concerns afternoon convection. The environment is slightly more supportive of thunderstorm development, and we have kept the small area of 20 percent rain chances in the forecast. The best chances will be across inland portions of Colleton County and the Charleston Tri-County region. Tonight: No significant changes are expected to the overall pattern in regards to high pressure dominating the weather pattern across the Southeast. Sfc winds will likely decouple early evening, with most areas experiencing light/calm winds away from the coast after midnight. Temps will remain mild, with lows generally ranging in the mid-70s inland to upper 70s/around 80 closer to the coast and across Downtown Charleston.
-- End Changed Discussion --
&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... This strong upper-lvl ridge that has been sitting across the Southeastern CONUS the last couple of days will finally begin to break down Wednesday afternoon. According to latest model guidance, 500MB heights on Wednesday morning will be ~594 dam, and then weaken to ~590 by Wednesday evening. While these are still high heights for the region, the highest heights will continue to remain just to the north. Temperatures will climb to the mid to upper 90s on Wednesday, with heat indices creeping ~104-106 in the afternoon. Over the last couple days, the NBM has been overplaying temperatures and dewpoints and thus, have adjusted the temperatures and dewpoints down a little in this period due to these recent trends. As of right now, heat indices remain below Heat Advisory criteria (108F), but this will continue to be monitored. Models have been fairly consistent with a weak surface trough forming over the Bahamas sometime on Wednesday and then meandering across the northeastern portion of the Gulf through the weekend. This feature will allow for some moisture to finally return back into the region. Additionally, SPC has placed the majority of region in a marginal risk and the far interior South Carolina counties in a slight risk for severe thunderstorms on Wednesday. According recent runs of the NAM and GFS, PWAT values will be ~1.75 to 2.0 inches for Wednesday afternoon. This will yield the chance for showers and thunderstorms to develop in the afternoon along the seabreeze. With strong instability ~1500-2500 J/kg, mid-lvl lapse rates ~7.5-8.0 C/km, and DCAPE values in excess of 1250 J/kg in the afternoon, thunderstorms on Wednesday could become severe with the main threat being damaging wind gusts. As this weak surface trough floats nearby, the aforementioned upper-lvl ridge will continue to weaken and eventually move offshore by the end of the week. Therefore, a more typical summertime pattern will set up for Thursday and Friday, with showers and thunderstorms developing in the afternoon along the seabreeze. Overnight lows will remain mild and only dip into the low to mid 70s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... This weak surface trough will meander across northeastern portion of the Gulf before eventually dissipating sometime on Sunday. A more zonal pattern will set up over the Southeastern CONUS thereafter. With moisture making a full return into the region, ensembles continue to indicate daily chances of rain through early next week. Temperatures will remain above normal for this time of the year. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
VFR conditions will prevail at KCHS, KJZI, and KSAV through 18z Wednesday. Any isolated thunderstorms this afternoon are expected to remain inland of the terminals. There is a better chance of thunderstorms Wednesday afternoon, but likely beyond the 18z TAF period. Extended Aviation Outlook: VFR will mainly prevail throughout the period, however there could be brief flight restrictions in the afternoon hours through the end of the week as rain chances make a return.
-- End Changed Discussion --
&& .MARINE... Today and Tonight: Atlantic high pressure will dominate the pattern across local waters, favoring conditions that remain well below Small Craft Advisory levels through tonight. In general, a westerly offshore wind associated with a land breeze will take place early, but sfc winds will gradually turn southwest mid-late morning, then south this afternoon as a sea breeze develops and pushes inland. Wind speeds should top out around 10 kt for a bulk of the day. Winds should then turn more southwest by mid evening, remaining around 10 kt through the night. Seas will generally range between 1-2 ft. Wednesday through Saturday: As a weak ESE swell continues to mix in, seas will remain around 1 to 3 ft. Expect winds at 5 to 10 kt to prevail throughout the period. It could become a bit gusty each afternoon with gusts up to 15 to 20 kt as the seabreeze pushes inland (gusts strongest across the immediate coastline and the Charleston Harbor). && .TIDES/COASTAL FLOODING... Astronomical tides will peak around 6.5 ft MLLW at Charleston with the evening high tide cycle this evening and Wednesday night. Afternoon winds will only be marginally supportive of increasing tidal departures each day. The evening high tide will likely peak around 6.8-6.9 ft MLLW each evening, falling just short of Coastal Flood Advisory criteria. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Heat Advisory until 8 PM EDT this evening for GAZ087-088- 099>101-114>119-138. SC...Heat Advisory until 8 PM EDT this evening for SCZ040-042>045- 047>052. MARINE...None. && $$ NEAR TERM...BSH/DPB SHORT TERM...Dennis LONG TERM...Dennis AVIATION...BSH/Dennis MARINE...Dennis/DPB