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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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073 FXUS62 KCHS 162042 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 442 PM EDT Fri Aug 16 2024 .SYNOPSIS... High pressure will remain over the area through most of this weekend. A cold front will push across the area Sunday night, then remain nearby through late week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A mid and upper trough will dig through the Great Lakes region, while an extensive mid and upper ridge stretches across the southern states and into the local region. High pressure at the surface will remain atop the area, while Hurricane Ernesto impacts Bermuda as it passes around 900 miles from the immediate region. A dry and stable air mass will encompass our counties, so we continue with the rainfree conditions, allowing us to dry out further. Earlier we were able to drop the Flood Advisory for Dorchester County near and along the Ashley River, but we still have some flooding in the Richmond Hill area near the Ogeechee River. Diurnal cumulus will dissipate this evening, and while there might be a few mid or high level clouds drifting through at times, skies will be mainly clear. Light or calm winds and the dry air mass will allow for another night with most temperatures below climo. But with a southerly boundary flow to develop and slight modification of the air mass, lows will be a bit warmer than the last two nights. Generally upper 60s and lower 70s inland from the barrier islands, with mid and upper 70s closer to the ocean. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Saturday: H5 ridge will build across the deep south, with a subtle ridge across the forecast area. At the sfc, weak high pressure will remain across the western Atlantic as a broad trough remains across the Foothills of the Carolinas. This pattern will support light south-southwest across the forecast area. However, as temperatures warm into the low to mid 90s, a weak sea breeze should develop Saturday afternoon and evening. Forecast sounding across the sea breeze indicate that the environment will remain weakly capped. Guidance does support some convection sourced from inland GA reaching inland SE GA during the afternoon, highlighted with SCHC PoPs. Saturday night, guidance indicates that a vort max will accompany the approaching H5 trough. The forecast will highlight SCHC across portions of the SC Lowcountry late Saturday night into Sunday. 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. Heat index values will peak near 108 across portions of the GA coast and the southern SC coast. Interesting setup across the region Sunday evening. Models indicate that an MCS will develop across the western Carolinas Sunday afternoon, then tracking east. The MCS is expected to reach the forecast area Sunday evening, pushing over the Atlantic Sunday night. Forecast soundings show CAPE values ranging from 1500-2000 J/kg, with modest values of DCAPE. Hodographs indicate a deep curved profile, with 0-6 km bulk shear around 30 kts and 0-3 km helicity around 300 m2/s2. This environment should support a few organized storm clusters, producing swaths of strong to severe wind gusts. In addition, it is possible, that a few supercells may develop ahead of the MCS. SPC has highlighted most of the interior counties with a Slight risk for severe thunderstorms. The region will remain under the H5 trough axis on Monday. Isolated to scattered showers and thunderstorms may develop across the coastal counties during the afternoon. High temperatures are forecast to range in the low to mid 90s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Aloft, an upper-level trough extending from extreme eastern Canada down to Florida Keys will stall nearby into mid-week before finally being pushed offshore over the weekend. By Monday night, this pattern should feature a building high pressure to the north as the cold front from the associated trough becomes stationary offshore. This set-up should allow for cold air damming, or CAD, to take place over the region allowing for cooler temperatures and drier conditions Monday through Thursday. However heading into Friday, due to some isentropic lifting, chances for some isolated to scattered showers become likely. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... VFR conditions are expected to prevail at the KCHS/KJZI/KSAV terminals through 18Z Saturday. Extended Aviation Outlook: A cold front is forecast to impact the region late this weekend/early next week, bringing the risk of brief flight restrictions within showers and thunderstorms. && .MARINE... This evening and tonight: Hurricane Ernesto will pass by Bermuda, while high pressure sits right overhead of the local waters. This will result in winds veering around to the SE and S through the night, with speeds mainly 10 kt or less. Guidance continues to be overdone on seas by about a foot, and as a result we have adjusted the forecast accordingly. We now show some 6 footers making it into the nearshore South Carolina waters between 8 pm and 4 am, continuing to back off on the start time of the Small Craft Advisory, valid during that time. Even that might continue to be a little overdone. On the Georgia waters, seas will remain 5 ft or less on the nearshore waters, so no advisory there. But the outer waters will experience 6 or 7 footers, so we continue the advisory on the waters 20-60 nm offshore. Saturday through Wednesday: Seas should decrease to 3-5 ft with light and variable winds early Saturday with high pressure in place. Saturday night into Sunday winds and seas will gradually increase ahead of an approaching cold front that is expected to push across the local waters Monday. Winds could surge from the SW to around 20 kts with gusts 20-25 kt Sunday night. In addition, seas could build up to 6ft across portions of the outer GA waters Sunday. Conditions will improve throughout the day Monday with seas dropping to 2-3 ft, and winds shifting northeast 10-15 kt for Tuesday and Wednesday. High Surf: Local guidance has been running about a foot or so larger than webcams would show, which has generally been 3 or 4 foot breakers at the coast. As a result we continue to refrain from issuing a High Surf Advisory, but we will continue to monitor. Rip Currents: So far we have received 7 reports of rip currents at Tybee Beach today. Since long period swell (13 to 15 seconds) from Hurricane will continue to impact the beaches through the weekend, we have a High Risk of Rip Currents at all beaches through Sunday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents through Saturday evening for GAZ117-119- 139-141. SC...High Risk for Rip Currents through Saturday evening for SCZ048>051. MARINE...Small Craft Advisory from 8 PM this evening to 4 AM EDT Saturday for AMZ350-352. Small Craft Advisory until 8 AM EDT Saturday for AMZ374. && $$ NEAR TERM... SHORT TERM...NED LONG TERM...Dennis AVIATION... MARINE...Dennis