Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
011 FXUS62 KCHS 121115 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 715 AM EDT Sat Sep 12 2026 .WHAT HAS CHANGED... Aviation section updated for the 12Z TAFs. && .KEY MESSAGES... - 1) The risk for showers and thunderstorms will continue through the weekend. && .DISCUSSION... KEY MESSAGE 1: The risk for showers and thunderstorms will continue through the weekend. Today: Satellite water vapor showed a mid-level trough extending across the Mississippi River valley, tracking east. East of the trough, a plume of deep moisture covered a large area from the Gulf across the Southeast U.S., PW values between 2-2.2" across SE GA/SC. RUC40 guidance indicates a few vort maxes within the moisture plume, with the consensus of the guidance indicating that one or two disturbances tracking over SE GA/SC this afternoon. The approach and passage of these mid- level disturbances combined with the sea breeze should focus the development of convection. MLCAPE during the heat of the afternoon is forecast to range from 1500 J/kg inland to 2500 J/kg along the coast. Given the deep moisture, DCAPE values are forecast to remain less than 1000 J/kg. The primary hazard this afternoon will be the potential for excessive rainfall rates, aided by high PW values and 850-300mb RH in excess of 70%. Isolated locations could see rainfall amounts exceed three inches. By late this evening, convection should dissipate with the spreading of outflow boundaries and diurnal cooling. Sunday: The mid-levels will consist of a weak trough moving over our area in the morning, then offshore during the afternoon. The surface pattern will be rather diffuse, with either a weak front well to our north or weak surface troughing over the Southeast U.S. Southwesterly flow will cause deep moisture to be over our area in the morning. PWATs should easily be above 2". This is well above normal per CHS sounding climatology and about 2 standard deviations per NAEFs. However, lower PWATs will build in from the west during the afternoon, keeping the highest PWATs along the immediate coast, before they are pushed offshore in the evening. The deterministic models and CAMs differ somewhat on the amount of shower and thunderstorm coverage. But most point to scattered coverage forming near the coast in the afternoon, then shifting offshore and dissipating in the evening. High temperatures will be a few degrees above normal, leading to modest instability. Additionally, higher DCAPEs build in from the west during the afternoon. So while we`re not expecting widespread severe weather, there could be a few hour window where strong to marginally severe thunderstorms cannot be ruled out along the coast. Locally heavy rainfall will also be possible. But the steering level winds may be just strong enough to limit significant flooding. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... 12Z TAFs: Light southwest winds with VFR ceilings at KCHS and KJZI this morning, KSAV should remain mostly sunny. This afternoon, showers and thunderstorms should focus along the sea breeze and approaching vort maxes. Each terminal will feature a PROB30 between 17-23Z for TSRA. Any thunderstorm may bring gusty winds and some periods of restrictions during moderate to heavy downpours. Each TAF, will indicate steady south winds following the sea breeze. Extended Aviation Outlook: Periodic flight restrictions will be possible Sunday afternoon due to showers and thunderstorms. Drier conditions return on Monday, possibly persisting through Wednesday. && .MARINE... Today and tonight: The pressure pattern will generally support south- southwest winds between 10 to 15 kts across the marine zones. Wave heights are forecast to remain between 2 to 3 ft. Extended Marine: The synoptic pattern will be unsettled on Sunday, but modest winds and seas are expected. Winds will ease Monday morning and afternoon, along with seas trending lower. But this will be short-lived because High pressure passing to our north will cause winds to shift to the northeast late Monday night and surge. A strong breeze will persist Tuesday into Wednesday, with wind-driven seas building during this time period. Small Craft Advisories will be needed for most of our waters beginning Tuesday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$