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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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038 FXUS62 KCHS 152338 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 738 PM EDT Thu Aug 15 2024 .SYNOPSIS... High pressure will build in from the north through late week. Another cold front may approach the area early next week, then remain nearby through late week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... This Evening: Most areas will remain rain-free with deep layer high pressure persisting across the Southeast United States. However, a few stray showers can not be ruled out along a subtle theta-E axis stretching across the local area in wake of a sea breeze progressing further inland. Tonight: The local communities will be situated between a strong mid level anticyclone along the southern tier of the country, with a trough in the western Atlantic. That trough will be responsible for lifting Hurricane Ernesto off to the north-northeast as it draws closer to Bermuda. We`ll be under the influence of high pressure covering the eastern seaboard. Diurnally induced cumulus (and light showers) will fade by or near sunset, leaving mainly clear skies locally for the remainder of the night. Winds will decouple and good radiational cooling will commence away from the coast. Based on how low temps were last night/early this morning, conditions should be a bit cooler with the 1000-850 mb thickness slightly less. This results in min temps in the mid-upper 60s west of US-17, with even some lower 60s in the Francis Marion National Forest. East of US-17 will experience lows down in the lower and middle 70s. Some of the statistical guidance shows some ground fog closer to daybreak, but given unfavorable condensation pressure deficits this shouldn`t be of any concern. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Friday: The forecast area will remain between a mid-level ridge centered over the Southern Plains and a long wave trough over the western Atlantic. At the sfc, a ridge of high pressure will remain over the Atlantic coast, providing the region with light east- northeast winds. Forecast soundings show a strong inversion centered at H7. The strong llvl inversion combined with sfc dewpoints in the 60s should yield little to now instability across the CWA on Friday. The forecast will feature dry weather with highs in the low 90s. A weak H5 ridge is forecast to ripple across the region Friday night into Saturday. At the sfc, high pressure will remain along the coast through the day. Given light south winds, dewpoints may increase to around 70 degrees during the afternoon. However, lingering inversion at H7 should provide the region with a cap, around 100 J/kg of CIN during the heat of the afternoon. High temperatures may increase a degree or two over values reached on Friday. Sunday: A cold front will slowly approach from the west through the day. Sfc winds are forecast to shift from the southwest, keeping the sea breeze along the coast through early afternoon. The sea breeze is expected to drift inland during the mid to late afternoon, resulting in dewpoints to climb into the mid to upper 70s. Scattered showers and thunderstorms are forecast to develop between the sea breeze and the approaching cold front. High temperatures are forecast to range in the low to mid 90s. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Sunday night into Monday: The details of the forecast will be determined by the placement and timing of the cold front. At this time, it appears that the cold front will reach the Atlantic coast around daybreak Monday morning. Guidance indicates that the environment along and ahead of the cold front will feature CAPE around 2000 J/kg and 0-6 km shear around 30 kts. This environment could support a few organized storm clusters or lines, resulting in strong to severe wind gusts. It is possible that a couple of severe events may occur late Sunday night into Monday. The forecast will feature 30-40 PoPs from Sunday night into Monday afternoon. Tuesday and Wednesday, the sfc pattern will feature ridging high pressure over the land as the old cold front remains stationary off the coast. This pattern may yield light east winds, allowing a sea breeze to develop each afternoon. Isolated to scattered showers and thunderstorms may develop during the PM. High temperatures should range near 90 each day. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... VFR conditions are expected to prevail at KCHS/KJZI/KSAV terminals through 00Z Saturday. Extended Aviation Outlook: Surface high pressure will yield VFR conditions through Saturday. A cold front is forecast to impact the region late this weekend/early next week, bringing the risk of brief flight restrictions. && .MARINE... This evening and tonight: Sea breeze circulations will push much further inland and fade, but there is still a modest gradient between high pressure inland and very distant Hurricane Ernesto. This will create mainly east or east-northeast winds up near 15 kt early on (gusts up to 20 kt across offshore Georgia waters), decreasing several knots overnight as winds back more northeast with land breeze influences. Seas will average around 3-4 ft across nearshore waters, and 4-5 ft across offshore Georgia waters. Some 6 footers will move in around 6 AM on the outermost Georgia coastal zone, so a Small Craft Advisory won`t start until 8 AM. Some small fore-runner swells (periods of 13-15 seconds) from Hurricane Ernesto will start reaching into the coastal waters late, an indication of things to come on Friday into the weekend. Friday through Tuesday: Swell wave from Hurricane Ernesto will increase across the coastal zones on Friday, lingering into Friday night. Wave heights are forecast to peak Friday afternoon, ranging from 4-6 ft across the nearshore waters to 6-7 ft across the outer GA waters. A Small Craft Advisory (SCA) has been issued for the outer GA waters from Friday morning through Friday night to highlight the seas. The far outer portions of the nearshore SC waters may see some 6 ft seas, but duration and coverages appears too limited for a SCA at this time. Otherwise, the pattern should yield east winds between 5-10 kts Friday afternoon, becoming light Friday night. Seas should decrease to 3-5 ft on Saturday. Sunday and Monday, a cold front will slide across the region. Winds ahead of the cold front may surge from the SW to around 20 kts with gusts in the low 20s Sunday night. In addition, sea may build to around 6ft across portions of the outer GA waters Sunday night. It is possible that SCA wind gusts and sea could develop Sunday night. Otherwise, wind and sea conditions may remain below SCA criteria through early next week. Rip Currents: Although the beaches are still not feeling impacts of Hurricane Ernesto`s swells, there have already been reports of 6 moderate to strong rip currents at Tybee due to local effects. The Moderate Risk of rip currents continues on the Georgia beaches into this evening, but we`ll keep Low Risk on the South Carolina beaches. Long period swell (13 to 15 seconds) from Hurricane Ernesto is forecast to reach the forecast area on Friday. This in combination with onshore winds will produce a high risk of rip currents at all area beaches on Friday. The threat for rip currents could persist into Saturday as well. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents from Friday morning through Friday evening for GAZ117-119-139-141. SC...High Risk for Rip Currents from Friday morning through Friday evening for SCZ048>051. MARINE...Small Craft Advisory from 8 AM Friday to 8 AM EDT Saturday for AMZ374. && $$ NEAR TERM...DPB SHORT TERM...NED LONG TERM...NED AVIATION...DPB MARINE...DPB