Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
046 FXUS62 KCHS 121117 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 717 AM EDT Sat Jul 12 2025 .SYNOPSIS... Weak high pressure will extend across the area into early next week. A surface front may sag into the area during the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, the ridge and anticyclone currently centered near south FL should start to take greater hold on the pattern across southeast GA and up the Southeast coast. At the surface, the setup will be typical of summertime with the subtropical high over the Atlantic to the east and a subtle inland trough. The ridge aloft starting to build a bit further north would seem to favor seeing a little less coverage than the past few days, especially for the southeast GA area. There isn`t much consistency in hi-res model guidance, though if you squint you could perhaps see a bit more coverage developing first inland closer to the Midlands in the mid to late afternoon and then pushing to the east or southeast towards the coast through the evening. However, much like the past few days, once convection gets going and throws out a few outflow boundaries we could see development just about anywhere. The severe threat does not look particularly noteworthy, with MLCAPE values of 2,000-2,500 J/kg, meager lapse rates, and DCAPE values only in the 500-700 J/kg range. As such, the forecast area is not included in an SPC Day 1 severe risk area. But, as with most summer days there will be the potential for an isolated severe storm, especially where the more significant boundary interactions occur. Locally heavy rainfall will again be a potential issue with the area remaining within a pocket of 2-2.25" precipitable water and relatively slow storm motion (~10 knots). So while most areas will see rainfall amounts of 0.50" or less, there could be isolated amounts of 1-2" where the heaviest storms track. Highs are forecast for the low 90s, with max heat index values mostly in the 102-106 degree range. Tonight: Clusters of showers and thunderstorms could linger into the mid to late evening hours, but should generally be on a diminishing trend. Then for the overnight hours, attention should again shift offshore for shower and thunderstorm development. Pretty typical summer night with lows in the mid 70s for most areas. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Sunday into Monday, an upper ridge will briefly build to our west, with increasing heights across the Southeast. High temps will be in the mid to upper 90s except near the coast where upper 80s to lower 90s will be the rule. Bermuda high pressure will prevail at the surface, maintaining a moist southerly flow into the area. Dewpoints are expected to surge into the mid to upper 70s, particularly over the eastern half of the area both days. Our latest forecast shows a few hours of heat indices of 106-110F over a significant chunk of the forecast area, so we may eventually need Heat Advisories for part of the area. A slight increase in mid-level subsidence from the upper ridging may limit diurnal convective coverage to be more scattered vs widespread. Tuesday could see greater convective coverage as a weak shortwave rotates around the northeast side of the ridge and interacts with a moderately unstable airmass. Temps should be a few degrees cooler than on Monday. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... A weak surface trough or front could stall over the area on Wednesday and Thursday, providing an additional focus for convection. Upper ridging then expected late week, though an active sea breeze and ample moisture should still allow for at least scattered showers and thunderstorms. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/... The 12z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. The main forecast challenge continues to be afternoon and evening thunderstorm chances. Current thinking is that the best coverage will be across southeast SC, so we have removed the TEMPO group at KSAV but maintained it at KCHS and KJZI. If a thunderstorm does directly impact any of the terminals, gusty winds and brief flight restrictions will be possible. Thunderstorm activity should dimish by the mid evening hours. Extended Aviation Outlook: The main concern will continue to be brief flight restrictions from showers and thunderstorms. The greatest threat window will be in the afternoon and early evening hours. && .MARINE... Today and tonight: Pretty typical summertime pattern expected across the local waters through tonight. Southwest winds will turn more southerly in the afternoon with a modest surge in wind speeds peaking in the afternoon and evening hours. Speeds should mostly top out in the 10-15 knot range but there could be some gusts up to 20 kt at times along the land/sea interface. Then overnight, winds will turn more southwesterly and even westerly late with speeds diminishing into the 5 to 10 knot range. Seas should mostly average 2-3 feet. Thunderstorms will again be a potential hazard as land- based storms develop this afternoon and try to move to the coast and the coastal waters through the evening. Frequent lightning and gusty winds will be the primary concerns. Sunday through Wednesday, southerly flow will continue as Atlantic high pressure remains off the coast. A decent sea breeze will develop each afternoon, with winds in Charleston Harbor potentially gusting close to 20 kt at times. No headlines expected. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...BSH SHORT TERM...JRL LONG TERM...JRL AVIATION...BSH/JRL MARINE...BSH/JRL