641 FXUS62 KCHS 301017 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 617 AM EDT Sun Jun 30 2019 .SYNOPSIS... A weak front will shift into the area late tonight through Monday before high pressure prevails through late week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Only minor changes were made for the sunrise update. H5 ridging will begin to reestablish itself today as the region gets caught between a weak shear axis/upper low along the upper Texas coast with a potent shortwave rotating across New England. Mid-level heights will rise ever so slightly through the day as the resulting ridge eventually links between the subtropical anticyclones over the Bahamas and Central Plains. The net result will be an increase in synoptic scale subsidence and less convection overall from what was experienced Saturday. Modified forecast soundings are reasonably unstable for early summer with no hint of a mid-level cap just yet, but low-level convergence fields look to weak and mainly confined to the sea breeze and a sharpening lee-side trough over the South Carolina Midlands/CSRA. Any convection that fires today will likely remained pinned to the sea breeze itself or in locations roughly along/south of the I-16 corridor where low- level moisture will be a bit deeper. A rogue shower/tstm could also approach areas adjacent to the CSRA which will be closer to the position of the lee-side trough, but this scenario is much more uncertain. Pops will be capped at 20% in these areas with 10% or less elsewhere. Westerly winds and a 1-1.5C rise in H8 temperatures will support highs in the lower 90s for many locations with 90 degree temperatures possibly reaching as far east the Intracoastal Waterway before a delayed sea breeze circulation forms. Dewpoints should mix out into the upper 60s/near 70 before surging back into the lower-mid 70s at the coast late behind the sea breeze. Heat indices will peak around 100F and well below the pre-July 1 Heat Advisory criteria of 105F. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... Tonight: Any lingering convection will dissipate after sunset with dry conditions prevailing overnight. A weak front will drop in from the north closer to daybreak, but will not have meaningful influence on local conditions. Lows will range from the lower 70s inland to the mid- upper 70s across the coastal counties and around 80 at the beaches. Monday through Wednesday: A large mid/upper lvl trough of low pressure shifting over the Northeast United States will help drive a weak front through the area Monday. Fropa is expected to be dry as the bulk of moisture is pushed south of the region before peak diurnal heating. A mid/upper lvl ridge will then begin to expand from the south/southwest across the region Tuesday, before becoming centered over the Southeast United States Wednesday. As this process occurs, a sfc lee trough of low pressure will develop just inland of the area, becoming more pronounced by Wednesday. Although the ridge aloft will help maintain dry conditions through at least Tuesday, a few showers and/or thunderstorms are possible by Wednesday, mainly well inland closer to the lee trough inland. Outside of a stray shower/thunderstorm Wednesday, the main issue will be the heat. Despite weak fropa Monday, warm high pressure following the front should support temps in the mid 90s away from the coast Monday afternoon. Monday night lows should range in the low/mid 70s. Temps will likely be warmer on Tuesday as high pressure extends across the region, then warmest on Wednesday as high pressure persists and becomes centered over the Southeast. Latest 1000-850mb thickness levels support temps in the mid/upper 90s Tuesday and Wednesday, warmest along and west of the I-95 corridor. A few locations could hit 100 degrees well inland Wednesday. These temps along with sfc dewpts in the lower 70s could produce heat index values up around 105 degrees Wednesday afternoon, falling short of Heat Advisory criteria for July. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... At the sfc, lee troughing will persist inland while a large mid/upper lvl ridge of high pressure remains centered over the Southeast United States. The setup will favor warm conditions across the area through late week as light southerly flow at the sfc occurs below a light west/northwest flow aloft. Although high pressure will dominate aloft, substantial heating could produce a few afternoon showers or thunderstorms Thursday, especially across inland areas closer to the lee trough. Latest 1000-850mb thickness levels suggest temps approaching the mid/upper 90s Thursday afternoon, before some mid-lvl energy approaches from the west/northwest and potentially brings greater chances of showers and thunderstorms through the weekend until a weak front approaches the area Sunday. However, high temps should still approach the low/mid 90s away from the immediate coast this weekend and early next week. Overnight lows will be mild, generally ranging in the mid 70s inland to upper 70s near the coast. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... VFR. Extended Aviation Outlook: VFR conditions should prevail at both KCHS and KSAV terminals. However, brief flight restrictions are possible during an isolated shower or thunderstorms Wednesday and Thursday afternoon/evening. && .MARINE... Today: A weak land breeze will give way to a sea breeze and some influences from a lee-side trough this afternoon allowing winds to back to the southwest. Speeds will generally remain 15 kt or less, but could gust near 20 kt at times along the Charleston County coast. Seas will average 1-2 ft. Tonight: West to southwest winds will prevail as the flow response to the approach of a backdoor front. Winds will surge somewhat with speeds averaging around 15 kt, but will be locally higher near 15-20 kt along the Charleston County coast. Seas will average 1-3 ft with offshore winds limiting sea growth near the coast. Monday through Thursday: Atlantic high pressure will remain well offshore as a weak front pushes south of the region on Monday. A mid/upper lvl ridge of high pressure will then expand over the coastal waters from the west/southwest mid week while a sfc lee trough develops inland. Given the setup, winds and seas are expected to remain below Small Craft Advisory levels during the period. However, northerly winds near 15 kt early Monday should quickly weaken and turn more southerly late in the day, then persist through mid week. Seas should range between 1-3 ft, highest in offshore Georgia and northern South Carolina waters. Waterspouts: High resolution guidance suggests a weak land breeze will setup off the coast early this morning. GOES-E IR imagery and surface observations suggest this feature is already beginning to form. This circulation could serve as a focus for waterspout development through mid-late morning after which conditions will become increasingly unfavorable as the sea breeze begins to form. Wind fields are a bit stronger than yesterday morning, so waterspout development will be a bit more marginal than the past two mornings, but certainly non-zero. && .TIDES/COASTAL FLOODING... There will be a risk for at least shallow coastal flooding across the coastal counties during the evening high tides through the middle of the week due to the approaching perigee, new moon and onshore winds. Coastal Flood Advisories could be needed, especially Monday and Tuesday evenings. && .EQUIPMENT... KCLX radar will remain down until further notice. Radar techs will be on site later today to diagnose and possibly fix the problem. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$