459 FXUS62 KCHS 231151 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 751 AM EDT Mon Jun 23 2025 .SYNOPSIS... High pressure will remain across the Southeast U.S. for the first half of this week, then slowly shift over the Atlantic thereafter. Hot and humid conditions are expected throughout the week with rain chances increasing by the second half of week as surface troughing begins to form over the region. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, a large/strong ridge centered across the Mid-Atlantic states will remain the dominating weather feature extending across the Southeast United States, leading to warm and mostly dry conditions locally along the western edge of sfc high pressure extending from the nearby Atlantic. Large-scale subsidence, strong sfc heating under sunny/mostly sunny skies and 1000-850mb thicknesses support highs in the low-mid 90s away from the beaches this afternoon. Most areas will remain dry, although an isolated shower/thunderstorm can not be ruled out completely given the summer like pattern and signs of weak lee troughing developing west of the local area mid-late afternoon. Despite warm temps, strong low-lvl mixing into a deep layer of dry air depicted on water vapor imagery and local model soundings suggest sfc dewpts to lower considerably during peak diurnal heating inland and thus limit maximum heat index values generally to 100-105 degrees. Any pooling of moisture along an inland moving sea breeze could temporarily increase heat index values a few degrees higher for a 1-2 hr period, primarily away from the beaches across the Tri-County Area, but heat index values should remain below Heat Advisory criteria. 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 under clear skies for areas away from the beaches mid-late evening, with the bulk of the area experiencing light/calm winds during the second half of the night. Hires guidance depicts considerably less fog potential across the local area late, but perhaps some shallow ground fog across Southeast Georgia a few hours prior to daybreak, mainly near the I- 95 corridor closer to the Altamaha River, where lower condensation pressure deficits reside. Temps will remain mild, with lows generally ranging in the lower 70s inland to mid-upper 70s closer to the coast and across Downtown Charleston. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... A strong upper-lvl ridge continues to build over the Southeastern CONUS throughout the week. According to model guidance, 500MB heights on Tuesday will be ~598 dam, and then weaken to ~594 over the next couple days. While these are very high heights for the region, the highest heights will remain just to the north. However, this will still produce a strong warming trend for the next couple of days. Temperatures will climb into the mid to upper 90s on Tuesday and Wednesday, with heat indices creeping ~105-107 in the afternoons. As of right now, heat indices remain just below Heat Advisory criteria (108F), but this will continue to be monitored. This sort of heat is not uncommon for this time year, however it is important to remember to stay hydrated and limit outdoor activity (esp. in the afternoon). With little moisture available and subsidence filtering into the mid-lvls on Tuesday, this will keep the forecast fairly dry and uncomfortably hot. Tuesday actually looks to be the hottest day of the week with temperatures making a run for the 100 degree mark. Some of the models have been hinting that a weak surface trough could form over the region sometime on Wednesday and allow for a cooler day than expected on Thursday with temperatures reaching into the low 90s. Simultaneously, this feature might advect enough moisture into the region to allow for some showers and thunderstorms to develop in the afternoon along the seabreeze on Wednesday and Thursday. Thus, 20-30% PoPs were added in the forecast for Thursday and Wednesday afternoon. Overnight lows will remain mild and only dip into the low to mid 70s. && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... This strong upper-lvl ridging pattern will finally begin to weaken by the end of the week as a weak surface trough tries to form over the region. This will allow for some moisture to return and some recent ensembles indicate a better chance for rain over the weekend and into early next week. Temperatures will remain above normal for this time of the year into the weekend. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... VFR conditions are expected at CHS/JZI/SAV terminals through 12Z Tuesday. However, shallow ground fog could remain at the SAV terminal shortly after 12Z this morning, then perhaps develop again an hour or two prior to daybreak Tuesday morning. Probabilities are too low to include MIFG at SAV in the latest TAF issuance. Extended Aviation Outlook: With the strong upper-lvl ridge in place over the Southeast, VFR should mainly prevail throughout the period. However, there could be brief flight restrictions in the afternoon hours starting on Wednesday through the end of the week as rain chances make a return. && .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, west/southwest winds in the 5-10 kt range this morning will turn south-southeast and peak around 10-15 kt this afternoon, highest across the Charleston Harbor and perhaps along beaches as a sea breeze develops, then shifts inland. Winds should then turn more southwest by late evening, remaining around 10 kt or less overnight. Seas will generally range between 1-2 ft. Tuesday through Friday: As a weak south-easterly swell continues to filter in, seas will be 1 to 2 ft and then gradually become 3 to 4 ft on Friday afternoon as a more easterly, stronger swell mixes in. Expect winds at 5 to 10 kt to prevail throughout the period as this upper-lvl ridge continues to sit over the region. However, by second half of the week, this ridge will begin to shift offshore as a weak surface trough scoots its way into the Southeast. 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). Rip Currents: A 1.5 to 2 ft, 8 second swell will impact the beaches through this evening along with a 10-15 kt onshore wind in place. Given these conditions are similar to yesterday with several rip currents reported along Tybee Island, GA, a Moderate Risk for rip currents is in place along Georgia beaches through this evening. && .TIDES/COASTAL FLOODING... The new moon is Tuesday night, which will yield higher astronomical tides. Winds should be from the SW, which would limit tidal anamolies. So while Coastal Flooding (mainly for the Charleston tide gauge) is not forecasted at this time, it won`t take much for it to occur, prompting an advisory. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...Dennis LONG TERM...Dennis AVIATION...Dennis/DPB MARINE...Dennis/DPB