Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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353 FXUS62 KCHS 230258 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1058 PM EDT Sat Jun 22 2024 .SYNOPSIS... A weak surface trough will linger near the Georgia coast through tonight. High pressure will then prevail over the western Atlantic through next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Tonight: Weak low pressure currently centered near the I-95 corridor across southeast Georgia will be slow to track north overnight due to weak steering flow in place. Although subsidence associated with mid-upper lvl ridging extending from the west will remain in place for much of the night, modest instability (SBCAPE around 2000 J/kg and PWATs near 2.0 inches) could support a few thunderstorms in addition to moderate showers along the northern edge of the low pressure circulation where low-lvl convergence will be greatest for the next several hours. Otherwise, dry air to the north will likely limit shower and/or thunderstorm coverage across much of Southeast South Carolina into late night hours, especially as instability wanes through the night. Late tonight, weaker instability does remain in place as the low pressure circulation attempts to slowly drift north. A few slowly moving convective elements could develop near Savannah/Beaufort Co area. Localized rainfall amounts could reach up to 3-4+ inches in this area, but widespread rainfall amounts will likely be closer to an inch or less. Further north (Charleston Metro), precip coverage will remain more limited for much of the night, but latest hires guidance does suggest an uptick in activity within a few hours prior to daybreak. Much will depend on how far north the low pressure circulation will track north overnight, before showing signs of dissipating heading into Sunday. Outside of this feature, some clearing should begin across far inland areas of southeast Georgia late tonight and with a relatively weak gradient in place could support radiational cooling that overlaps lingering boundary layer moisture for a few hours. Should this occur, patchy fog could develop across southeast Georgia, mainly inland from coastal counties. Fog remains out of the forecast at this time. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... A weak surface low along the coast will open and be absorbed into the approaching troughing/front well inland Sunday. Still, ample low level moisture lingers, with showers and storms likely to develop along the resultant sea breeze by Sunday afternoon. Widespread cloud cover across much of the area will limit the instability somewhat, but instability climbing to 1000-2000 J/kg of MUCAPE along the sea breeze could bring some stronger thunderstorms, with gusty winds and lightning the primary threats. Further inland across SE GA, dry air will work in as the low dissipates and less cloud cover will bring warmer temps (into the mid 90s) and lower rainfall chances. Heat index values will climb to around 100 Sunday afternoon with warmer temps, but less humidity inland, and greater humidity and relatively more moderate temps closer to the coast. A weak shortwave ridge will extend across southeast GA Sunday night, then a shortwave trough will drop into southern SC from the northwest on Monday. A weak surface cold front will slowly drift into the area on Monday. Increasing thicknesses combined with pre-frontal compression will result in toasty temperatures in the mid to upper 90s. The deepest moisture is forecast to move off the coast early Monday afternoon, so afternoon instability will not be particularly strong. A decent sea breeze should develop and move inland in the afternoon, but there will also be some mid-level subsidence working against buoyant parcels. We have isolated to scattered showers and thunderstorms in the afternoon. Heat indices will top out between 104 and 108F, just shy of needing a Heat Advisory. A weak northwest flow will continue aloft on Tuesday while a weak surface high is centered across inland areas. Large scale subsidence will result in another hot day with highs in the mid to upper 90s. Surface dewpoints should mix out across inland southeast GA, while moisture pooling occurs closer to the SC/GA coast. The greatest risk for Heat Advisory conditions with heat indices above 108F will be across coastal GA and far southern SC. The main forcing for convection will be from the sea breeze, though a few subtle upper shortwaves are also possible. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... A developing upper trough across the eastern United States and deep tropical moisture spreading into the area is expected to support greater coverage of mainly diurnal showers and thunderstorms through the long term period. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... KSAV: Periods of MVFR cigs are expected along the northern edge of a sfc low that continues to draw moisture/showers (and perhaps a thunderstorm) across the terminal this evening and much of the night. IFR cigs/vsbys are also possible should moderate showers impact the terminal. Latest guidance indicates a greater chance of IFR cigs within a few hours of daybreak Sunday as well, but sfc winds are expected to make a westerly turn as the low pressure center drifts north and gradually weakens late morning into early afternoon. Although some MVFR cigs could linger across the terminal after 16Z Sunday, conditions should eventually improve to VFR at the terminal during the afternoon. It`s possible a sea breeze could return a few showers and/or thunderstorm to the terminal Sunday afternoon, but confidence in timing/occurrence remains to low to include in the latest TAF issuance. KCHS/KJZI: A few showers could bring tempo MVFR cigs to the terminals this evening, but a majority of guidance suggests showers to return within a few hours prior to daybreak, leading to MVFR cigs early to mid morning hours. Can not rule out the possibility of IFR cigs/vsbys during morning showers. Conditions should then slowly return to VFR during the afternoon, but showers and/or thunderstorms could bring flight restrictions temporarily. Confidence is too low to include afternoon showers/thunderstorms in the latest TAF issuance. Extended Aviation Outlook: Mostly VFR. However, convection will bring brief flight restrictions, mainly each afternoon and evening. && .MARINE... Tonight: Weak low pressure slowly tracking north across southeast Georgia and into southeast South Carolina late will continue to bring moderate southeast to south winds across the waters. Some gusts to 20 kt are possible across local waters along the eastern edge of low pressure centered across southeast Georgia, but conditions are expected to remain below Small Craft Advisory levels as the pressure gradient slackens a bit overnight. Seas will average between 2-4 ft across nearshore waters and 4-5 ft across offshore Georgia waters this evening, then slowly show signs of subsiding heading into daybreak Sunday. Extended Marine: A slightly enhanced gradient is expected to return Sunday night between an inland trough and offshore high pressure. Wind gusts could approach 25 kt beyond 15 NM from the coast, and seas may reach 5 ft over outer portions. Otherwise, a fairly typical summertime pattern will occur, with the strongest winds along the coast each afternoon as the sea breeze develops. Rip Currents: A moderate risk continues through Sunday due to onshore winds and a moderate southeast swell. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...CEB/JRL LONG TERM...JRL AVIATION...DPB/JRL MARINE...CEB/JRL