Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 211651 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1251 PM EDT Thu Sep 21 2017 .SYNOPSIS... High pressure will prevail through this weekend. The high will weaken and shift inland as Hurricane Maria tracks northward off the Southeast U.S. coast through the first half of next week. && .NEAR TERM /THROUGH TONIGHT/... This Afternoon: Weak sfc high pressure will persist over the area with a fair amount of moisture characterized by PWATs near 1.5-1.6 inches. Strong sfc heating under partly cloudy skies will contribute to mixing out some of this moisture, but a light onshore wind will help maintain sfc dewpts in the lower 70s closer to the coast this afternoon. Given the setup, we could see a few showers and/or thunderstorms develop along a weak seabreeze circulation initially, before a mid/upper lvl trough extending northeast to southwest across the region helps spawn additional showers and/or thunderstorms over parts of Southeast South Carolina and Southeast Georgia during peak heating hours mid afternoon into early evening. Precip coverage could be higher over inland parts of Southeast South Carolina where forcing from the mid/upper lvl trough is greatest, but moisture mixing out of the low-lvls will likely limit the overall potential. Highs will range in the upper 80s near the coast to lower 90s inland. Tonight: A few of the high resolution models suggest isolated evening convection could linger along a sagging mid level trough axis across our far northern zones around the Santee Cooper Lakes. With the loss of diurnal heating and warm mid level temps, we only hung onto 20 POPs prior to midnight while suspecting models could be overdone. We also opted for patchy fog mentions across northwest zones late tonight where various guidance progs suggest the higher chances. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Weak upper troughing and some increased moisture will persist across the area Friday into Saturday and this along with a fairly weak sea breeze will support a few showers and thunderstorms, mainly in the afternoon on Friday and just in GA on Saturday. Building high pressure from the north later Saturday and Sunday should keep things dry this period. Temperatures will stay above normal, generally upper 80s during the day and around 70 at night. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Inland high pressure will persist through early next week while confidence is increasing that Hurricane Maria will remain offshore of the Southeast U.S. coast as it tracks north through the middle of next week. Some showers could skirt coastal areas early next week as Maria passes by but otherwise mainly dry conditions are anticipated. Temperatures look to stay above normal. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... VFR conditions are expected to prevail at both CHS and SAV terminals through 18z Friday. However, a shower and/or thunderstorm could impact either terminal this afternoon/evening. Additionally, MVFR vsbys will be possible at either terminal due to fog late tonight into daybreak, but confidence with the timing and duration of the event are too low to include at either terminal. Extended Aviation Outlook: Low probability for brief flight restrictions in early morning fog and/or low clouds Saturday morning and in mainly afternoon showers/thunderstorms Friday at KCHS/KSAV and at KSAV Saturday. && .MARINE... This Afternoon and Tonight: Fairly tranquil conditions are expected within weak sfc high pressure over the coastal waters. In general light/variable winds will become south/southeast 5-10 kt this afternoon, highest near the land/sea interface. Seas will range between 1-2 ft nearshore and 2-3 ft in offshore Georgia waters, mainly in a long period swell. Thursday through Monday: No significant concerns before swells from Hurricane Maria nearing the southeast Bahamas later this week begin to impact the waters Thursday night or Friday. Advisories will be likely for the offshore waters starting Friday and the nearshore waters starting Friday night. Seas could build to 10 feet or more near the Gulf Stream Saturday night and persist in Monday, although much depends on the exact track/strength of Hurricane Maria. Rip Currents: Astronomical influences and a lingering long period ground swell component will support a low-end moderate rip current risk at area beaches today. Swell from offshore Hurricane Maria will create more significant rip current risks this weekend into the middle of next week. && .TIDES/COASTAL FLOODING... A light onshore wind along with long-period swell and astronomical influences could lead to minor coastal flooding along parts of the Southeast South Carolina coast during/near high tide early tonight. A Coastal Flood Advisory could be needed. Powerful surf created by offshore Hurricane Maria will drive significant wave run-up, which could cause further beach erosion this weekend into early next week. Also, the potential for shallow salt water flooding will persist through early next week around the times of high tide, particularly along the SC coast. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...RJB LONG TERM...RJB AVIATION...DPB MARINE...DPB/RJB TIDES/COASTAL FLOODING...

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