Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
903 FXUS62 KCHS 131759 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 159 PM EDT Sun Jul 13 2025 .SYNOPSIS... Weak high pressure will continue to build across the region through the week. && .NEAR TERM /THROUGH TONIGHT/... This Afternoon: The region will remain positioned under generally high pressure at the surface. Aloft, troughing off the coast of the Mid-Atlantic states will yield northwesterly flow aloft, as well as influence the flow at the surface. This set up will make for interesting storm motions this afternoon, generally north to south. Models are depicting less coverage than the last several days, however the same hazards persist as storms could be strong to severe and have the potential for heavy rainfall. The HREF has highlighted the coastal counties for the best chance of precipitation. The HREF additionally shows a 10% probability for >3 inches of rainfall across far northern Charleston and Berkeley Counties. Once convection begins to initiate across the coastal counties additional storms are possible along any outflow boundaries that are created. PWAT values east of I-95 are around 2.1-2.2 inches according to SPC Mesoanalysis. Locations impacted directly by thunderstorms could receive 1 to 2 inches of rainfall. Heat index values as of 2PM are generally between 100-105 across the forecast area, just shy of Heat Advisory criteria. As convection begins this afternoon some relief in the heat is expected. Tonight: Showers and thunderstorms should diminish in the early evening hours, however some precipitation could linger into the overnight period depending on how the boundaries interact. The remainder of the overnight period should be rain-free, with temperatures in the 70s. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... A weak upper-lvl ridge will remain across the Southeast over the next couple of days. Simultaneously, a surface low will try to develop off the Georgia and Florida coastline and track west into the Gulf on Monday night. At the surface, rich moisture will continue to be advected into the region with PWAT values ~2.0 inches. This will be more than enough moisture to spark up some showers and thunderstorms each afternoon as the sea breeze pushes inland. Expect temperatures to be in the mid to upper 90s on Monday, with upper 80s to low 90s on Tuesday and Wednesday. Heat index values on Monday will range from 100 to 106 degree in the afternoon hours (especially in Southeast Georgia). These values remain under Heat Advisory Criteria (108F), therefore we will not be issuing a Heat Advisory for Monday at this time. Deep moisture and moderate instability will support locally heavy rainfall with any shower and/or thunderstorm that develops, and isolated strong to severe thunderstorms are possible each afternoon. Overnight lows will remain mild and only dip into the low to mid 70s (with warmer temperatures closer to the beaches). && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... A deep upper-lvl ridge will develop over the Southeast late this week through the weekend, as an area of low pressure moves westward across the north central Gulf. The Bermuda high will continue to advect an ample amount of moisture across the Southeast with PWAT values remaining ~2.0 inches throughout the period. With moderate instability expected to build in the afternoons, expect typical summertime weather with showers and thunderstorms initiating off the sea breeze each day. Temperatures will remain slightly above normal for this time of the year. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... VFR conditions will initialize the 18Z TAFs at KCHS/KJZI/KSAV. Showers and thunderstorms are forecast to develop along the coastal counties this afternoon and a TEMPO for TSRA has been maintained at all three terminals. Showers and storms are expected to diminish with nightfall with prevailing VFR through the remainder of the 18Z TAF period. Extended Aviation Outlook: VFR will mainly prevail throughout the period, however brief flight restrictions are possible within showers and thunderstorms that develop in the afternoon and/or evening hours. && .MARINE... This Afternoon and Tonight: Conditions will remain well below Small Craft Advisory criteria through this afternoon and tonight. For the afternoon and evening, winds will flip around to become southerly under the influence of the sea breeze circulation with speeds still mostly 10 knots or less. Right along the land/sea interface speeds could top out in the 10-15 knot range, including Charleston Harbor. Then overnight, winds will continue to be quite weak, diminishing to less than 10 knots. Seas should average around 2 feet, but could be up to 3 feet around the 20 nm line and beyond. Much like the last few days, thunderstorms are expected to develop along or just inland of the coast and then move southward to the coast or out over the coastal waters. Frequent lightning and strong wind gusts will be the primary threats. Monday through Thursday: Expect generally southerly 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). Southeasterly swell will continue to mix into the local waters throughout the week. Seas will be 1 to 2 ft, then increase to 2 to 3 ft on Tuesday evening. Otherwise, no marine concerns expected. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...CPM SHORT TERM...Dennis LONG TERM...Dennis AVIATION...CPM/Dennis MARINE...CPM/Dennis