536 FXUS62 KCHS 030824 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 424 AM EDT Sat Aug 3 2019 .SYNOPSIS... Weak low pressure will pass offshore today. A stationary front will remain across the region through early next week. Then, a weak surface trough will prevail inland with high pressure in the Atlantic. && .NEAR TERM /THROUGH TODAY/... Through Daybreak: Radar data, surface observations and RAP surface wind analysis suggest weak cyclogenesis is occurring about 100 NM east of Jacksonville, Florida early this morning coincident with an area of enhanced lightning activity detected earlier. 03/07z isallobaric data show surface pressures are slowly dropping with falls of 1-2 mb/3hrs noted off the central and northeast Florida coast. A large swatch of showers/tstms developing off the coast is associated with a strong region of surface moisture convergence in excess of 50 g/kg/12hr induced by a modest easterly fetch ahead of the sharpening low. This band will move onshore soon and impact coastal areas for the next few hours before dissipating. Pops through daybreak will range from 60-70% a the coast to 20-30% well inland. Today: Guidance is similar in showing the low becoming better defined later this morning as it becomes situated underneath the right entrance region of 40-70 kt jet streak extending from the South Carolina Midlands into the Delmarva. It is becoming increasingly likely that most of the convection associate with the low will remain just offshore the South Carolina and Georgia coasts with the strongest deep-layered moisture transport being redirected into eastern North Carolina. A few of the HREF members, including the more reliable RAP and H3R, do suggest a band of showers/tstms could setup along the Charleston County coast by mid-morning as the surface low makes it closest approach, but confidence on how this will play out is only moderate a best. However, it is becoming increasingly clear that guidance is trending drier overall for Southeast South Carolina and Southeast Georgia for today. Pops from sunrise through late morning will range from 70% across middle-upper Charleston County to 20-30% inland. Adjustments will likely be needed later this morning once convective trends are more firmly established. Once the low makes it closest approach, vertical cross sections show weak DNVA and drying associated with the subsident right exit region of another jet streak propagating out the northeast Gulf of Mexico moving into the area. This weak downward motion coupled with meager instability induced by extensive cloud cover will likely keep far inland areas rain-free through early afternoon, after which some significant breaks in the cloud canopy could support isolated to perhaps scattered convection as temperatures warm into the upper 80s to lower 90s. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... Tonight: Weak high pressure will build into the region tonight. The boundary layer should decouple for many areas as the pressure pattern becomes rather nebulous through the overnight hours. As skies clear and winds go calm/light, could see some patchy ground fog develop. A weak surface trough looks to form along the coast closer to daybreak which could spark off isolated showers along the beaches and the adjacent coastal waters. Low-end mentionable pops will be highlighted in this area. Lows will range from the upper 60s/lower 70s inland to the mid-upper 70s at the beaches. Sunday through Tuesday: The mid-level pattern will remain relatively consistent with troughing prevailing over the Southeast. At the surface, a stationary front will stretch either nearby or into our region Sunday. The front is forecasted to meander during the daylight hours, then shift southwest and offshore Sunday night. It should then dissipate off our coast by late Monday. Plenty of moisture will be in place across our area. PWATs should remain ~2.0", despite what the aforementioned front does. But the models remain in good agreement showing widespread showers Sunday. They should decrease in coverage/intensity Sunday night as the front moves away. Though, showers/thunderstorms should persist over the coastal waters and possibly bring occasional impacts to the immediate coast. Another round of showers/thunderstorms is expected on Monday, probably comparable to Sunday. Following another decrease in coverage/intensity Monday night, another round is expected on Tuesday. Though, the 00Z models indicate the daytime coverage/intensity should be less on Tuesday than the previous two days. The abundant moisture should help limit the overall severe risk. If we were to get any strong or marginally severe storms, it would probably be on Sunday with the front. Otherwise, the main risk continues to be heavy rain. Localized flooding is a concern if there is training of cells, especially on Sunday. Even with all of the rainfall, models remain steadfast in showing temperatures reaching normal values. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Mid-level troughing will persist over the East Coast for much of the long term. Though, models hint it may start trending offshore on Friday. At the surface, weak troughing will prevail inland while high pressure is over the Atlantic. Models hint at maybe a front approaching midweek, but it doesn't appear to make it to our area. Otherwise, expect the typical afternoon showers/thunderstorms with seasonal temperatures. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... KCHS: Mostly VFR. Shower activity over the Atlantic is expected to remain just east of the terminal today, possibly brushing it at times. Will carry VCSH through mid-morning with rain-free conditions thereafter as the best rain coverage should be pulling away by then. KSAV: Expect passing showers for the next several hours with near MVFR cigs. Will carry tempo MVFR conditions through 09z with prevailing MVFR cigs 09-15z as cigs drop as weak low pressure passes by. Expect VFR thereafter with the risk for shower activity diminishing. Extended Aviation Outlook: Showers/thunderstorms will bring occasional flight restrictions, mainly each afternoon and evening. && .MARINE... Through Tonight: Weak low pressure will be moving across/near the coastal waters this morning. Winds will slowly shift with time. Winds will remain less than 15 kt with seas 2-4 ft. Vsbys could drop to less than 1 NM at times in pockets of heavier convection. Winds will shift west and northwest tonight in the wake of the low. Winds will average less than 10 kt with seas 2-4 ft. Friday through Tuesday: No Small Craft Advisories are expected for the extended forecast. The synoptic pattern will consist of a stationary front remain across the region early next week, then dissipating. By the middle of next week, a weak surface trough will prevail inland with high pressure in the Atlantic. && .TIDES/COASTAL FLOODING... The combination of astronomical and meteorological influences will continue to generate elevated tides this weekend. This evening's high tide is likely to reach Coastal Flood Advisory levels for the entire coast. The Sunday night high tide may reach Coastal Flood Advisory levels for the Southeast South Carolina coast. If heavy rainfall occurs around this high tide, then flooding will be exacerbated, especially for the Charleston Peninsula. On Monday, falling astronomical tides along with winds paralleling the coast should keep tides below advisory levels. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$