Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 240836 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 436 AM EDT Sat Aug 24 2019 .SYNOPSIS... A cold front will cross through the region today and tonight, then stall near the coast on Sunday. Low pressure is expected to pass well offshore early next week, before another cold front impacts the area later in the week. && .NEAR TERM /THROUGH TONIGHT/... Pre-dawn: A cold front was moving south across the Carolinas, still north of our region early this morning. Dry weather has prevailed overnight to this point as convection associated with a fairly well-defined MCV dissipated earlier. Weak low level moisture and speed convergence along coastal zones may result in a few showers/tstms around daybreak but the majority of the area should remain dry. Today: The pattern will favor unsettled weather conditions as a cold front drops south into the area while deep moisture builds, leading to increasing clouds and expanding diurnal convective rains. The greater potential for showers and a few tstms during the mid/late morning hours should be across our northwest tier of zones and perhaps along the Charleston County coast in the vicinity of a decent stability gradient and near the tail of the weak remnant MCV drifting toward the SC Pee Dee region. We will otherwise see surface heating across the remainder of the region with temps warming toward 90 degrees after midday in Southeast GA. This afternoon: A complex mesoscale environment is anticipated as convection become scattered to locally numerous across the region, especially along and north of I-16 where deep layered moisture convergence is progged along the frontal zone. We maintained categorical POPs along our northwest fringe of zones from Millen and Sylvania GA, northeast in SC bordering the Midlands. Likely POPs down to I-16 and then chance POPs into the zones bordering the Altamaha River. Deep layered instability is rather unimpressive with warm mid levels and poor lapse rates, severe weather potential looks low but stronger tstms may be possible to the west of I-95 where frequent mesoscale boundary interactions are hinted by various CAMs. A flux of Atlantic moisture along with elevated PWATs suggest heavy downpours will accompany tstms and localized ponding water in low lying areas and on area roadways is possibly with any persistent deep convection. Tstms along coastal areas near time of mid afternoon high tides would be an issue but confidence in timing this occurrence is low at this time. Tonight: The front will drop south of the area while high pressure builds south to the lee of the mountains and surface low pressure shifts east of the Florida coast toward the Gulf Stream. Scattered rains and a few tstms will continue into the evening hours across the region with instability on the wane and coverage likely decreasing inland areas. Shower chances will linger into the night with light northeast winds and expanding low clouds after midnight and especially toward Sunday morning. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... At the start of the period, surface high pressure will be building inland while a cold front stalls offshore and to the south. This general wedge-like pattern will remain in place through Monday. The main deviation will be a low that is forecast to develop near the Florida peninsula, which will then track northeast well off the Southeast coast. The National Hurricane Center has high probabilities for tropical development of this low. Some discrepancies remain in regards to timing and strength of the low, but consensus has the center staying far east of the area. The highest rain chances will be focused across southeast Georgia in proximity to deeper moisture and best forcing both Sunday and Monday. Areas further north and inland should see less activity, especially on Monday. Limited instability will keep severe threat pretty low. Pockets of heavy rainfall will be possible with fairly weak storm motions and 2+ inch PWats. Models hint at a weak wave of low pressure shifting across the region on Tuesday. Shortwave energy and plenty of moisture will promote another fairly wet day. Current rain chances are in the 40- 60% range, highest across the Georgia zones. Temperatures throughout the period are expected to be at or below normal. Highs Sunday and Monday will mainly stay in the mid 80s, then warm to upper 80s/near 90 on Tuesday. Lows will be in the 70s. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... A tropical low off the mid-Atlantic coast Tuesday night will continue to lift northeast away from the region on Wednesday. Another cold front is forecast to cross the area later Wednesday or Thursday. The front will likely stall off the coast through late week while high pressure builds inland. Given the front lingering in the vicinity, rain chances will remain in the forecast. Highest PoPs will be near the coast. Temperatures are expected to be near normal. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Conditions are expected to be VFR a large portion of the time at both KCHS and KSAV this morning. However, there are concerns for possible restrictions at KSAV between about 10Z and 13Z Saturday due to fog and/or stratus. There then looks to be scattered to numerous SHRA/TSRA across the local region this afternoon and evening as a cold front draws closer from the north. Aided by a low level flow off the ocean and upper difluence, there is a good chance that at least occasional flight restrictions (if not more prolonged sub-VFR weather) will occur. For now we have just VCTS and CB clouds at both terminals, but adjustments will definitely be required in later TAF issuances with the potential for some heavy rainfall. Extended Aviation Outlook: Sub-VFR ceilings possible Sunday into Monday behind a front stalled offshore. Brief restrictions also possible with any shower/thunderstorm that impacts the terminals through mid-week. && .MARINE... Light and variable winds this morning will tend to become onshore this afternoon as a cold front moves into the waters. Winds will increase late tonight as the gradient tightens between high pressure to the north and low pressure off the Florida coast. Wind should increase closer to 15 kt late tonight and seas will build to 2-4 ft. Waterspouts: Conditions were looking favorable for waterspouts this morning, we will access the potential for a Marine Weather Statement after examination of the first visible satellite images. Sunday through Thursday: Marine conditions will deteriorate Sunday into Monday as the pressure gradient tightens between high pressure inland and a tropical low passing well offshore. Small Craft Advisories could be needed for portions of the waters as northeast winds increase and seas build. Conditions will improve Tuesday as the low pulls away from the local area. A cold front will impact the area later in the week. Additional marine concerns are not expected at this time. Rip currents: Increasing east/northeast winds could contribute to an enhanced risk of rip currents on area beaches late this weekend into early next week, especially if tropical low pressure intensifies while tracking well offshore. && .TIDES/COASTAL FLOODING... Astronomical tides will be running close to minor Coastal Flood Advisory levels next week and onshore winds could lead to even higher tides, mainly during the evening high tide cycles starting Monday. In addition, there is the potential for some heavy rain around the times of high tide which could exacerbate any flooding issues. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...ETM LONG TERM...ETM AVIATION...ETM MARINE...ETM TIDES/COASTAL FLOODING...

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