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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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301 FXUS62 KCHS 180433 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1233 AM EDT Sun Aug 18 2024 .SYNOPSIS... A cold front will move through our area Sunday night into Monday. High pressure will then gradually build in from the north through the remainder of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... The atmosphere is steadily stabilizing with nocturnal cooling. A few showers could still occur across the far interior where a number of convective outflows are working southeast. Slight chance pops were maintained for a few more hours there. Lows from the lower 70s well inland to the upper 70s/near 80 at the beaches and Downtown Charleston are on track. && .SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY/... Sunday: The mid-levels will consist of a strong trough over the East Coast. An impulse of energy should round the base of the trough and move over our area during the evening hours. Further up, a jet stream initially to our north will become located over our area by the evening and overnight. At the surface, High pressure will initially be located off the Southeast Coast. It`s expected to move further offshore as time progresses. Additionally, a cold front will be located to the west of the Appalachians at daybreak, it`ll gradually shift to the east and southeast, becoming located over or just to the west of our area by daybreak Monday. Flow around the High and ahead of the front will usher moisture from the Gulf of Mexico into our area. PWATs should peak in the 2-2.25" range in the afternoon. The combination of 850 mb temperatures, low-level thickness values, and compressional heating ahead of the front will cause high temperatures to be several degrees above normal. They are forecasted to be in the lower to middle 90s, except cooler at the beaches. Heat indices should rise close to 108 degrees, mainly along the coast. But it`s marginal whether we`ll need Heat Advisories. The combination of the heat and moisture will generate a decent amount of instability. MLCAPEs should approach the 1,500-2,000 J/kg range with steepening lapse rates. 0-6 km bulk shear should be in the 20- 35 kt range. Combined with lift from the approaching front, convection is expected. Models and the long range CAMs disagree on the exact timing and some of the evolution. But we anticipated isolated to scattered convection across our area in the afternoon. Then, a cluster or line of storms originating well to our west and northwest should move through our area. It should be across our inland counties late in the afternoon, making its way to the coast in the evening. Severe storms with damaging winds are the main concern, so the SPC has our area under a Slight Risk, which seems reasonable. Heavy rainfall is also a concern given the saturated grounds. But these storms should be moving fast enough to limit enormous rainfall amounts. Either way, Flood Advisories cannot be ruled out. The convection will move offshore later in the evening and overnight as drier air builds in from the west. Lows will generally be in the 70s. Monday and Tuesday: The mid-levels will consist of a strong trough hovering over the East Coast. The front should be located off our coast Monday morning. However, it could stall and meander offshore through Tuesday. Meanwhile, High pressure should gradually build in from the northwest, with its periphery reaching into our region. The High should dominate the land forecast, leading to mainly dry conditions, except for maybe a stray shower along the immediate coast each afternoon. Highs will only be a couple of degrees cooler behind the front. Expect them to be in the lower to middle 90s on Monday and the upper 80s to lower 90s on Tuesday. Lows will be in the upper 60s to lower 70s. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... High pressure will build in from the north, causing an inland wedge pattern. Isolated to at most scattered showers and thunderstorms could develop during the afternoon and evening hours each day. However, modest subsidence will limit the overall coverage of convection. High temperatures will gradually lower each day, but will remain within a few degrees of normal. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... 18/06z TAF Discussion: KCHS/KJZI/KSAV: VFR for much of the period. Scattered showers/tstms are expected to develop late this afternoon into this evening for the coastal corridor. Confidence is somewhat diminished as a number of the near term convective models are showing a number of possible scenarios for both coverage and timing for convection. There seems to be a broad consensus that the periods from roughly 22-02z at KCHS/KJZI and 23-03z at KSAV will have the best chances for impacts at the various terminals. For now, the 06z TAFs were trended to use VCTS in the above mentioned periods. The introduction of TEMPO or prevailing groups for TSRA may need to be considered in later TAF cycles as confidence in timing/coverage increases. Extended Aviation Outlook: A cold front will move through our area Sunday night into early Monday, bringing brief flight restrictions due to convection. VFR is expected to prevail beginning later Monday. && .MARINE... Overnight: Per recent buoy observations and 00z WW3 output, the start time for the Small Craft Advisory for the Georgia offshore waters was moved up by several hours as 6 ft seas should arrive a bit quicker than expected. Sunday through Thursday: Winds and seas will increase ahead of an approaching cold front on Sunday. Seas should be around 6 ft across the GA waters beyond 20 nm, so we have a Small Craft Advisory in place. The front should move through the waters early Monday, then stall just to the east of our waters later Monday. This will cause conditions to improve. By Tuesday, winds will shift out of the northeast with speeds around 10-15 kt. A surge of winds is possible on Thursday as the pressure gradient becomes enhanced due to an inland wedge of High pressure to our north. Rip Currents: Sunday: Long period swell around 12 seconds from distant Hurricane Ernesto will continue to impact the coast. A High Risk for rip currents will be in place across all local beaches through Sunday evening as a result. Monday: Long period swell around 11 seconds will gradually subside, but continue to bring impacts to the coast. We have a Moderate Risk of rip currents for all of our beaches. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents through this evening for GAZ117-119-139- 141. SC...High Risk for Rip Currents through this evening for SCZ048>051. MARINE...Small Craft Advisory from 5 AM early this morning to 9 AM EDT Monday for AMZ374. && $$