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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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275 FXUS62 KCHS 121149 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 749 AM EDT Mon Aug 12 2024 .SYNOPSIS... A stationary front will remain just to the west through Tuesday before dissipating. Weak high pressure will build in from the north during the middle of the week and prevail into the latter part of the week. && .NEAR TERM /THROUGH TONIGHT/... Stalled boundary remains draped through the eastern and central Carolinas into central Georgia with high PWAT/dewpoint air lingering along the southeast coast. Surface boundary may make some push toward the southeast coast through tonight, spurred on by expanding surface high pressure from the Upper Midwest across the Ohio and Tennessee Valleys. But very warm and humid conditions will continue through today before slightly cooler and less humid air tries to press into the region through midweek. Today: Once again, daytime heating will quickly drive temperatures into the lower 90s by noon, topping out in the lower to middle 90s for highs this afternoon along with MLCAPE values building to 1500-2500 J/Kg, perhaps a little lower across southeast Georgia as some lower dewpoint air tries to wrap into southeast Georgia. Similar to the last few days, light southwesterly low level flow will promote an active sea breeze developing and pressing inland through the afternoon. Should be enough to kick off shower/thunderstorm development early this afternoon with the greatest coverage of convection anticipated across the SC Lowcountry where low level convergence will be maximized and higher dewpoint air/instability will reside. Morning forecast will continue to advertise isolated to scattered showers/storms through the afternoon, with the highest precip chances across the southeast SC quad-county area. Organized severe weather threat remains low. But given the high instability and DCAPE values around 1000 J/Kg, a few strong storms will again be possible. Of course the bigger concern rests with our ongoing hydro issues as any storms will be capable of producing localized heavy rainfall on top of already wet grounds and elevated river levels. Much of the forecast area remains in a marginal risk for excess rainfall exceeding flash flood guidance. Meanwhile, Areal Flood Warnings and Flood Advisory remain in effect through early to mid-morning due to lingering flooding issues/elevated rivers and will be reevaluated later this morning. Meanwhile, high surface dewpoints and temps warming into the lower to middle 90s (90-95F) will again push Heat Index values toward or exceeding Heat Advisory criteria along the coastal corridor. Given the anticipated greater coverage of convection across the quad-county area and the impact on temps, not as confident that heat index values will attain advisory criteria, or at least not for an extended period of time. More confident further south from Beaufort County to the Altamaha, with lower coverage of convection anticipated and a Heat Advisory has been issued for those locations valid from noon until 6 pm. Tonight: Convection will diminish through the evening hours with quiet conditions overnight. Lows will dip back into the upper 70s to around 80. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... Tuesday: A weak surface front and area of low pressure across the Midlands will meander across the area through the day. A trough across the Northeast and Mid-Atlantic states will dig into the Southeast late which will push those surface features southward. Low-level convergence near the front, in addition to the sea breeze, will be enough to support at least scattered showers and thunderstorms during the afternoon and evening. Guidance favors southeast South Carolina for the greatest coverage with conflicting coverage across southeast Georgia. The forecast reflects at least slight chance POPs across our southern zones considering PWATs in that area will be around 1.7 inches. With plenty of instability, we can`t rule out a stronger storm or two, especially where boundary interactions occur. However, the overall severe threat will be low. Also, some storms could produce locally heavy rainfall. Given that ground conditions are wet and some areas are still experiencing flooding, there is little to no tolerance for additional rainfall. Therefore, any thunderstorm that develops will have the potential to quickly produce flooding issues. High temperatures are forecast to reach the low to mid 90s and overnight lows will be in the low to mid 70s away from the coast. Wednesday: A trough across the Northeast and Mid-Atlantic states will continue to dig into the Southeast, helping to nudge the aforementioned weak front offshore. Models suggest a very narrow swath of deep moisture passing over the area associated with the front, in addition to upper forcing, which will again bring at least scattered convection during the afternoon/evening hours. Wednesday will be touch cooler with highs in the upper 80s across our southeast South Carolina counties and low 90s for our southeast Georgia counties. Min temps will largely bottom out in the low to mid 70s with some inland spots in the upper 60s. Thursday: Weak high pressure will begin to build in from the north, along with relatively drier and cooler conditions. This will keep rain chances to a minimum. The current forecast features slight chance to chance POPs, which may even be overdone. Highs are && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... Weak high pressure will linger for a day or two before a cold front quickly approaches. This will result in lesser chances of diurnal convection during the weekend. The front could pass over the forecast area early next week, which could lead to higher rain chances. Temperatures should rise a degree or so each day with highs back into the low 90s this weekend, around near-normal for this time of year. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Isolated to scattered showers and thunderstorms are possible again this afternoon along the sea breeze with high-res guidance suggesting the higher precip chances will be at CHS. 12Z terminal forecasts will include VCSH for the CHS terminal after 19Z. No mention for JZI and SAV for now. Any showers/storms will diminish through the evening hours with VFR conditions persisting overnight. Extended Aviation Outlook: Brief flight restrictions are possible in afternoon and evening showers/thunderstorms through the period. && .MARINE... Today: Southwest winds continue across the coastal waters today with winds trending a bit more southerly this afternoon with the sea breeze. Sustained winds of 10 to 15 kts with some higher gusts. Seas should generally range between 2 to 3 ft in a mix of southeasterly medium period swell and southerly wind chop. Tuesday through Saturday: A deep offshore ridge will result in southwest flow around 10 kt or less Tuesday. Wednesday afternoon, high pressure will begin gradually build in from the north after a weak front departs southward which will cause winds to shift out of the northeast. Seas will average 2-3 feet; however, by the end of the week seas will start to rise as increasing swell arrives from what could be a strengthening tropical system over the open Atlantic. Small Craft Advisories could be needed for a portion of the marine zones for 6 ft seas. && .HYDROLOGY... Most of southeast Georgia and southeast South Carolina remains quite vulnerable to additional rainfall following the 10-20 inches of rain that fell last week. Many areas are still experiencing ongoing flooding, and any additional rainfall from thunderstorms will certainly not help conditions improve. Scattered to numerous thunderstorms are forecast each afternoon and evening through midweek, and any locally heavy rainfall could produce new areas of flooding. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Heat Advisory from noon today to 6 PM EDT this evening for GAZ116>119-137>141. SC...Heat Advisory from noon today to 6 PM EDT this evening for SCZ047>049-051. MARINE...None. && $$