Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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067 FXUS62 KCHS 171132 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 732 AM EDT Tue Sep 17 2024 .SYNOPSIS... Low pressure across the Carolinas will weaken through mid week. High pressure should develop inland late week into the weekend. && .NEAR TERM /THROUGH TONIGHT/... Early morning update: Pesky lower cloud cover continues to linger across a good portion of southeast South Carolina and sky forecasts have been tweaked accordingly. Otherwise, no other changes made to the going forecast. Stacked low pressure center (previous PTC8) is located near the central South Carolina/North Carolina border. Respectable wedge of drier air continues to wrap around the western and southern flank of the system and into our area with some upper 50s dewpoints noted over the far western/southwestern part of the forecast area. Still a fair amount of lower cloud cover across southeast South Carolina and parts of southeast Georgia, but getting eroded along the southern/western edges as the drier air spreads into the region. Today: Remnant surface low of PTC8 will languish across the inland southeast region through the day, underneath a somewhat cutoff/closed mid-level low...but with any lingering precip associated with the system displaced well north/west of the forecast area. Drier air wrapping around the southern flank of the system should gradually erode away the remaining lower cloud cover this morning. However, daytime heating may lead to scattered to perhaps broken Cu development later this morning and through the afternoon...and there may be some cloud cover that gradually rotates back into the western part of the forecast area late in the day. But with some sunshine, a warmer day is on tap compared to Monday with highs ranging from lower to middle 80s...coolest readings where cloud cover remains the most persistent. Tonight: Closed upper level low will continue to drift across the southeast region while deeper moisture and associated cloud cover continues to rotate back into the region leading to overall partly cloudy conditions. Light winds will allow temperatures to fall back into the 60s at most locations with temperatures running a little warmer along the coast. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Wednesday: A weak mid-level low will be centered across the Mid- Atlantic states and be slowly moving east during the day. The 500/ 300 MB dry air that was in place Tuesday, will be a thing of the past as the low continues to occlude. The day will start out with partly cloudy skies and PWATs around 1.9" (between the 75th and 90th percentile for this time of year). By the afternoon, the atmosphere will start to destabilize, and with plentiful moisture to work with, have continued the trend of slowly raising and expanding the chance PoPs for Wednesday afternoon. Synoptically, the region is on the divergent side of the trough axis, but just barely. However, the low is slowly heading east with weak height falls and DCVA over the area. This would imply weak forcing for ascent, and a return of afternoon showers and thunderstorms. High temperatures will also recover into the mid to upper 80s as thicknesses respond to the filling mid-level low (1000/ 850 MB thicknesses rise to 1410 m). Low temperatures Wednesday night will be in the upper 60s to lower 70s. Thursday: The barotropic low will begin to open up and become absorbed by another low over the Canadian Maritimes. As this occurs, a weak boundary will approach the area from the northwest. A sea breeze will try to get going, but likely become pinned along the coast before washing out. Expect high temperatures in the mid to upper 80s with 1000/ 850 MB thicknesses around 1410/ 1415 m). Low temperatures Thursday night will be in the upper 60s to lower 70s. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Ensemble guidance has come into better agreement in the extended period with the GEPS, GEFS, and EPS all showing the mid-level low slowly exiting the Mid-Atlantic coast this weekend with mid-level heights rising for coastal SC and GA. This has allowed the forecast to trend much drier with temperatures near normal. Friday, the mid-level low will exit the East Coast of the United States with another wave over the Canadian Maritimes heading east/ southeast. As this occurs, high pressure will slowly build into New England and ooze down the east side of the Appalachians. Dry conditions are forecast with highs in the mid 80s and lows in the mid to upper 60s. Lower dewpoints will also filter into the region helping to bring down the humidity. Sunday into Monday surface high pressure will remain in control with no precipitation expected. Afternoon temperatures will remain in the mid 80s with lows in the lower to mid 60s. Relative humidity values will also remain comfortable as dewpoints stay in the 60s. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Scattered to broken MVFR cloud cover continues to linger across southeast South Carolina and the CHS/JZI terminals early this morning, but will thin out and trend VFR over the next few hours. VFR conditions will then prevail at both terminals through 12Z Wednesday. At SAV, VFR conditions are anticipated through 12Z Wednesday. Extended Aviation Outlook: Wednesday: Prevailing VFR. A return of afternoon showers and thunderstorms is forecast which could temporarily restrict cigs and vsbys. Thursday: Morning MVFR cigs possible with prevailing VFR in the afternoon. A few afternoon showers and thunderstorms are possible which could temporarily restrict cigs and vsbys. A weak boundary will cross the terminals late Thursday turning the winds from the northeast. Friday and Saturday: Some MVFR cigs are possible early Friday morning, then VFR through Saturday as surface high builds in from the north. No precipitation is expected. && .MARINE... Today: Per recent marine observations, winds/seas have pretty much dipped back below Small Craft Advisory criteria across all marine waters. Therefore, all marine headlines have been cancelled. West to southwest winds will dominate through today before backing more southerly tonight. Wind speeds of 10 to 15 knots anticipated this morning, diminishing to 5 to 10 knots this afternoon and tonight. Seas of 3 to 5 feet are anticipated today, subsiding to 2 to 4 feet tonight. Wednesday: Morning showers and thunderstorms will be possible with winds out of the southeast around 10 kt. Seas 2 to 4 ft. Thursday: Another round of morning showers and thunderstorms are possible with a weak boundary crossing the waters Thursday night. Winds will turn from the northeast around 10 kt. Seas 2 to 4 ft. Friday: Northeast winds will slowly start to increase in speed 10 to 15 kt as surface high pressure builds in from the north. Wind gusts of 15 to 20 kt possible, or below Small Craft Advisory criteria. Seas 3 to 4 ft. Saturday: Northeast winds 15 to 20 kt with gusts 20 to 25 kt. Seas around 4 ft. A Small Craft Advisory might be required as the pressure gradient tightens from building high pressure. Rip Currents: Lingering swell of around 3 ft every 10 seconds and astronomical influences from the full moon and perigee will maintain a High Risk of rip currents for all beaches through today. && .TIDES/COASTAL FLOODING... As we continue into mid to late week, the risk for at least minor flooding will continue for Charleston and Coastal Colleton Counties due to high astronomical tides with the full moon on September 17th. Beaufort County, SC, south to McIntosh County, GA: Waters levels could be close to minor flood levels later this week as onshore winds return. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents through this evening for GAZ117-119-139- 141. SC...High Risk for Rip Currents through this evening for SCZ048>051. MARINE...None. && $$ NEAR TERM...Adam SHORT TERM...Haines LONG TERM...Haines AVIATION...Adam/Haines MARINE...Adam/Haines