685 FXUS62 KCHS 230956 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 456 AM EST Fri Nov 23 2018 .SYNOPSIS... A low pressure system will move through tonight through Saturday. A cold front will then move through Monday followed by high pressure. && .NEAR TERM /THROUGH TONIGHT/... Pre-dawn: Strong high pressure centered over New England continues to wedge south into the forecast area, resulting in a tightening pressure gradient and increasing breezes across the region. Breezy to windy conditions were ongoing on the beaches and barrier islands but latest indications were too borderline for wind advisories but we will monitor trends with the pinching gradients. Rains were still off the coast and skies ranged from mainly clear to the north of I-16, to cloudy conditions along coastal areas from Hilton Head southward through immediate coastal GA. The strong northeast flow may be responsible for some significant coastal flooding around high tide this morning, please see the tides/coastal flooding section. Today: A very complicated synoptic setup both surface and aloft as strong thermal and moisture gradients dominate the southeast states from north to south in the lower levels, anchoring tight low level pressure fields. Aloft, an upper jet segment extending across Florida will exit offshore while a strengthening jet digs into the Gulf Coast region. The forecast today continues to show unsettled weather developing along southern coastal areas and gradually spreading north and inland this afternoon. Clouds are expected to increase during the morning hour as isentropic ascent builds while warm air advection spread atop the wedge inversion. Temps will likely reach max levels by early in the afternoon before thickening clouds and rains tend to develop over more land areas. We kept most areas shy of 60 degrees throughout the day, lowering some readings over southeast GA from the previous forecast. Inland areas closer to the CSRA and SC Midlands may keep dry all day as models initially keep rains along and east of I-95. The tight pressure gradient will keep cool northeast flow going with breezy to windy conditions on the beaches and barrier islands where winds could frequently gust over 30 mph. Tonight: A progressive mid level short wave will move from the Southern Plains into the western Carolinas by 12Z on Saturday. Models break out more in the way of widespread rains, especially across coastal areas and nearly all of Southeast SC. There is some uncertainty on how far coastal trough can move inland after midnight, perhaps only into SC coastal zones where low level moisture and convergence would be maximized. A few models suggest an inch of rain is possible overnight in this area but most should fall after this evening's high tide and prior to Saturday's morning high tide. We continue to indicate likely to categorical POPs with temps ranging from the mid to upper 40s inland to the lower/mid 50s coast. Some lightning strikes could occur close the coast as the stronger upper forcing moves through but we mainly tstms for the adjacent waters again on this package. && .SHORT TERM /SATURDAY THROUGH MONDAY/... Low pressure will quickly pull northeast away from the forecast area Saturday. Latest guidance indicates rain will end from southwest to northeast, generally by early afternoon, though some model variation exists. Behind the low, a noticeably drier atmospheric column will be in place for much of Sunday with moisture levels increasing late in advance of a developing low pressure system over the central plains. This system will track northeast across or near the Great Lakes, pulling the next cold front through the forecast area Monday. As the front nears, moisture levels will increase greatly Sunday night into Monday, and slight chance POPs are warranted during this period considering increasing lift as the upper trough approaches. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... Based on the latest guidance, rain chances diminish by Monday afternoon behind the cold front, with dry high pressure persisting through at least mid-next-week. Coastal troughing could develop by late next week, increasing precipitation chances. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... VFR for much of the night at both KCHS and KSAV with conditions dropping to MVFR mid-late morning Friday. Gusty winds >20 kt will be possible at both terminals late tonight and will linger through the end of the 00Z TAF period. Risk for shower activity will increase quickly after 20, especially at KSAV where we introduced some rain late. We have rain breaking out at KCHS toward the end of the 06Z TAF cycle. Extended Aviation Outlook: Flight restrictions likely into Saturday as low pressure impacts the area. Surface conditions look to improve Sunday but brief flight restrictions will be possible overnight Sunday into Monday as a cold front crosses the region. VFR conditions are then expected to prevail at both terminals into mid- next-week. && .MARINE... Hazardous conditions are expected over the marine waters today with Gale Warnings in effect. We extended the Gales to mid afternoon with an SCA for the Charleston Harbor. Seas will build to 7-9 ft near shore and up to 11 ft offshore. The winds will tend to subside across GA waters tonight as the coastal front moves closer. Winds should remain strong and gusty this evening along SC waters but also tend to subside late as a wave of low pressure rides along the coast. A continuing tight surface pressure gradient will lead to Small Craft Advisory conditions over the nearshore coastal waters through late Saturday and offshore Georgia waters through early Sunday. Another round of Small Craft Advisories will be possible Monday as a cold front crosses the waters. High pressure will then persist into mid-next-week. High Surf: Local surf height guidance shows a possible window this morning of 5 ft breakers along the SC/GA coast. We will monitor for the potential of a High Surf Advisory. Some beach erosion is possible given the above normal tides. && .TIDES/COASTAL FLOODING... Strong northeast flow had developed along the coast overnight. Based on the latest forecast trends, it appears the chances for major coastal flooding were increasing given latest guidance. Tides are expected to peak 7.8-8.2 ft MLLW in Charleston Harbor and 9.9-10.3 ft at Fort Pulaski. We have upgraded the Coastal Flood Watch to Warning this morning. Expect Hwy 80 between Wilmington Island and Tybee Island will be closed due to saltwater inundation. A Coastal Flood Advisory was also issued for Tidal Berkeley County. Strong onshore flow through tonight combined with increasing astronomical effects will likely result in minor to moderate coastal flooding with the morning high tide Saturday. Coastal Flood Advisories are expected. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Coastal Flood Warning until 10 AM EST this morning for GAZ117- 119-139-141. SC...Coastal Flood Warning until 10 AM EST this morning for SCZ048>051. Coastal Flood Advisory until 10 AM EST this morning for SCZ052. MARINE...Gale Warning until 4 PM EST this afternoon for AMZ350-352-354- 374. Small Craft Advisory until 1 AM EST Saturday for AMZ330. && $$ NEAR TERM... SHORT TERM...JMC LONG TERM...JMC AVIATION...JMC MARINE...JMC TIDES/COASTAL FLOODING...