978 FXUS62 KCHS 110854 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 454 AM EDT Sat Aug 11 2018 .SYNOPSIS... Low pressure will persist near the region through the weekend. A weak front could drift into the area during the middle of next week. High pressure will then prevail during the second half of the week before weak low pressure returns next weekend. && .NEAR TERM /THROUGH TONIGHT/... Pre-dawn: Mainly quiet conditions with a spotty shower possible as a very weak short wave traverses the forecast area. The land breeze should ensure that any significant convection occurs off the coast. A very warm and humid summer morning with readings close to 80 degrees along the coastal corridor to the mid 70s well inland. Today: Ridging of the past couple of days has weakened and a broad upper trough was settling across GA and the Carolinas. Mean low level flow will back to a more southwest component and this alone suggests weaker capping today with potential for enhanced moisture convergence along the sea breeze corridor this afternoon and early evening. Moisture is forecast to deepen today in the 850-500 MB layer and PWATs rise above 2 inches forecast across most of the area. There will be some mid and high level clouds around this morning and temps will warm to around 90 not long after midday at many areas. We maintained highs in the low to mid 90s with the sea breeze coming off the SC beaches quicker today, readings will be not be quite as warm along the ocean front. Convection: Since convective temps are in the 90-91 degree range early on, showers and tstms initiation most areas after 18Z with the main focus along the sea breeze corridor. Isolated to scattered convection is expected to develop from mid to late afternoon with increasing coverage late in the day as outflow boundaries and the sea breeze interact. We maintained chance POPs averaging near 40 percent most areas inland from U.S 17. DCAPE values as high as 800-1000 J/kg are displaced off to the west this afternoon but soundings certainly support potential for some strong updrafts which could result in precip-loaded microbursts and an isolated severe wind threat. If upstream convection arrives from the W-NW late, the severe risk would be greater well inland. Tonight: Convective rains could linger into the evening hours many areas with coverage dependent on the extent of the sea breeze convection during the late day hours. Areas along and east of I-95 may see isolated to scattered showers and storms redevelop past the midnight hour. This would be due to coastal moisture convergence and the arrival of another weak mid level short wave. Lows should average mid 70s inland and upper 70s close to the coast. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Sunday: A fairly unsettled weather pattern is anticipated to start off the week as a nearly cutoff mid/upper lvl low shifts over the Ohio River Valley. South of this feature, a weak sfc trough will extend over much of the Mid-Atlantic and Southeast states, just inland and to the north of the area for much of the day. A light southwest flow along with abundant sfc heating should support high temps in the lower 90s away from the coast and PWATs that approach near 1.75 to 2.00 inches. The setup suggests scattered showers and thunderstorms developing near the trough axis earlier in the day, before activity drifts into inland areas during the afternoon and/or evening. A few showers and/or thunderstorms can not be ruled out along the seabreeze as well. Precip activity should wane during early night hours due to the loss of daytime heating. Overnight lows should range in the low/mid 70s. Monday: The center of a mid/upper lvl low will likely advance over the Northeast and Mid-Atlantic states, helping a sfc trough and/or weak front slowly shift toward the region from the north. Guidance suggests a fairly pronounced h5 shortwave sweeping along the southern base of the mid/upper low, shifting over Southeast South Carolina earlier in the day, then over Southeast Georgia later in the day. Ahead of this shortwave, a southwest flow will likely advect deep moisture into the region, characterized by PWATs near 2.0 inches over most areas, while sfc temps warm into the lower 90s, helping SBCAPE approach 1500-2500 J/kg. These unstable conditions in combination with forcing associated with the arriving shortwave and some upper lvl divergence associated with a passing h25 jet could lead to a fairly active afternoon/evening in regards showers and thunderstorms, some of which could be organized and potentially strong/severe. Strong wind gusts and heavy rainfall would be the primary threat with thunderstorms. Most activity should shift offshore during early overnight hours. Overnight lows should range in the low/mid 70s. Tuesday: Chances of showers and thunderstorms should persist into the afternoon as a sfc trough and associated weak front gradually shift toward the Southeast coast. However, convective activity should trend towards coastal locations and eventually offshore as the parent mid/upper lvl low to the north shifts off the Mid- Atlantic and Northeast coast while the weak sfc front attempts to push off the Southeast coast. High temps should peak in the lower 90s outside shower and thunderstorm activity. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Drier conditions are anticipated mid week as high pressure builds over the region Wednesday/Thursday while sfc low pressure is less pronounced inland. Other than a few afternoon showers/thunderstorms, the pattern should support slightly warmer conditions with high temps peaking in the low-mid 90s. Higher precip chances could return next weekend as the sfc trough becomes more pronounced inland while a front shifts toward the Mid-Atlantic states. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... VFR conditions will prevail at the KCHS/KSAV terminals. We have introduced VCTS late afternoon into early evening on this cycle as the trough pattern in the mid levels appears to be enough to allow for the potential scattered sea breeze convection. Extended Aviation Outlook: Brief flight restrictions are possible each afternoon/evening with showers and thunderstorms. Otherwise, VFR conditions are expected at both CHS and SAV terminals. && .MARINE... Persistence forecast for the most part, southwest synoptic flow will back south over GA waters this afternoon with enough gradient to support flow increasing back to 15 kt with some higher gusts at time. Along the SC coast, winds will also build to 15 kt with occasional G20 kt possible later in the day and this evening. Through Tonight, seas will generally average 2 to 3 ft. Tstms look more likely after midnight tonight with some strong storms possible locally. Storm motions should mainly be side or slightly offshore with coverage more prevalent beyond 20 NM. Sunday through Thursday: Conditions are expected to remain below Small Craft Advisory levels through the middle of next week. However, a somewhat tightened pressure gradient between low pressure inland and high pressure offshore will support southwest/south winds near 15-20 kt through much of the week. Shower and thunderstorm coverage should also increase over coastal waters on Monday, especially as a weak front attempts to shift offshore by the middle of the week. Seas will range between 2-4 ft into Tuesday, then slowly subside to 1-3 ft mid to late week. Rip Currents: While we are forecasting a Low Risk of rip currents at the beaches today, due to astronomical influences it won't take but a little higher wind than now forecast to bump the risk into the moderate range during the afternoon hours. && .TIDES/COASTAL FLOODING... The Perigean Spring Tide due to the New Moon and the Perigee will contribute to elevated high tide levels into early next week. The evening high tides could produce shallow coastal flooding, mainly over the weekend. Coastal Flood Advisories are possible. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...DPB LONG TERM...DPB AVIATION...DPB MARINE...DPB TIDES/COASTAL FLOODING...