Area Forecast Discussion
Issued by NWS Charleston, SC

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066 FXUS62 KCHS 150310 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1010 PM EST Wed Nov 14 2018 .SYNOPSIS... Low pressure will affect the area into Thursday with cool and dry high pressure then returning through this weekend. A cold front could move through early next week with a few showers followed by cool and dry high pressure once again into the middle of next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A broad and weak area of low pressure over north-central Florida will travel north-northeast and into our nearby Georgia Atlantic waters after midnight, reaching near the Charleston County coast around 12Z Thursday. During this transition, forcing will become maximized with deep moisture and strong dynamics in place due to a 40-50 kt low level jet and difluence associated with the upper jet passing inland over the Southeast. This will lead to widespread moderate rains developing, along with pockets of occasional heavy rains. Localized minor flooding will become a concern. We considered adding mention of t-storms over the South Carolina coastal zones, but with the track of the surface low to mainly stay over the ocean, we opted not to include. Still a stray t-storm is possible late. Rain cooled conditions have prompted us to lower temps, both hourly and for minimum temps a bit in many areas. However, with the track of the low approaching late, we have shown rising temps over parts of Charleston and Berkeley County. Gusty winds will persist, especially over the coastal corridor, as speeds reach as high as 30 or 35 mph. Previous discussion... A deep and tropical-like plume of moisture will extend across the area, with PWat as much as 170-180% of normal for mid November. This along with increasing and strengthening isentropic ascent with cool air damming in place to our north- northwest, and increasing forcing from an approaching wave of low pressure from Florida, which hugs the coast as it rides northeast, will lead to widespread rainfall all areas. A strong low level jet and difluence from the upper jet will further lead to large scale forcing for ascent, and potentially some locally heavy rains. Our evening update as slowed down the onset of rainfall over to the locations mainly over the north and east counties until the late evening and overnight, with likely to categorical PoP west and southwest. Depending upon if any instability get move onshore of the coastal plain of the area overnight as the coastal warm front attempts to move onshore, there could be a risk of isolated t-storms, and higher rainfall rates. This could result in the potential for localized flooding. The strength of the low level jet and the packed gradient between the in-situ wedge and the approaching low will lead to northeast and east winds as high as 30-35 mph along the coastal corridor. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... Relatively calm conditions will prevail through the period as low pressure pulls away from the region and high pressure builds in from the west. Rain will quickly end from southwest to northeast through the day Thursday with dry conditions prevailing Thursday Night into Saturday. Clearing conditions will ensue Thursday in the wake of the low with clear to mostly clear skies prevailing thereafter. Temperatures will only warm into the mid-upper 50s Thursday and Friday then moderate into the mid 60s by Saturday. Lows Friday Night will range from the mid 30s well inland to the mid-upper 40s at the beaches. Could see patchy to scattered frost develop across the far interior just before daybreak Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Dry weather will prevail through early next week as cooler high pressure moves into the area. A weak area of low pressure may develop offshore and cause a few showers mainly near the coast. Temperatures should mostly stay near normal. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... Rain has been slow in developing at and near KCHS and KSAV this evening, but eventually it will develop and overspread the terminals during the late evening and overnight as lift increases ahead of an approaching wave of low pressure from the south and southwest. MVFR conditions early in the valid 00Z TAF cycle will lower to IFR as the rain occurs, and continues into at least Thursday morning. As the low pulls away the rest of Thursday, the rain will end, and there should be at least some improvement back into the MVFR range after 15-16Z. An additional concern tonight will be winds, both surface and in the lower levels. NE winds will be gusty at the surface as the pressure pattern tightens between an inland wedge and the approaching wave. Also, a 45-50 kt jet will traverse the area for a few hours from about 04-09Z, leading to low level wind shear at both terminals. Extended Aviation Outlook: No concerns. && .MARINE... Overnight: Low pressure will ride north-northeast through the area, passing through all but the AMZ350 waters prior to daybreak. There is a strong pinching of the gradient between this approaching feature and an inland wedge that will generate NE winds as high as 25-30 kt with gusts near or in excess of 35 kt across most of the Atlantic waters. As a result we have Small Craft Advisory headlines in effect for AMZ350, AMZ352 and AMZ374. Across the AMZ354 waters and in Charleston Harbor we have strong Small Craft Advisory conditions, for NE winds of 20-25 kt with some higher gusts. Seas will be about as high as they can get in the absence of tropical weather; 8-12 ft in the Atlantic, with 2-3 foot waves in Charleston Harbor. Based on the recent radar trends and elevated instability expected across the coastal waters, we have added mention of a slight chance of t-storms across the outer Georgia waters through the night, which will expand into the Charleston County Atlantic waters after midnight as the surface low approaches. Thursday through Monday: Conditions will gradually improve across the local marine area Thursday as low pressure moves away from the area. Seas are expected to drop below Small Craft Advisory thresholds Thursday morning across the nearshore waters and Thursday afternoon for the Georgia offshore waters Thursday evening. From Friday on, northwest winds will turn northeast over the weekend with speeds 15 kt or less. Seas will range 2-4 ft from Friday through Monday. High surf: Gale conditions will cause elevated seas to continue, as the offshore seas within 20 nm reach as high as 8-11 ft, and 5 foot breakers occur in the surf zone, especially along the northeast and east facing beaches. A High Surf Advisory remains in effect. && .TIDES/COASTAL FLOODING... Strengthening northeast winds will lead to increasing positive tidal anomalies tonight. The high tide after midnight may experience departures around 1.5 ft MLLW at both Downtown Charleston and Fort Pulaski. While this is below our coastal flood criteria, there remains a concern that steady rains falling around that time may result in a mix of minor fresh and salt water flooding. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Surf Advisory until 5 AM EST Thursday for GAZ117-119-139- 141. SC...High Surf Advisory until 5 AM EST Thursday for SCZ051. High Surf Advisory until 8 AM EST Thursday for SCZ048>050. MARINE...Gale Warning until 1 AM EST Thursday for AMZ352-374. Gale Warning until 5 AM EST Thursday for AMZ350. Small Craft Advisory until 10 AM EST Thursday for AMZ354. Small Craft Advisory until 4 AM EST Thursday for AMZ330. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... TIDES/COASTAL FLOODING...

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