textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 was updated. The Aviation section was updated for the 12z TAFs.

KEY MESSAGES

- 1) Unsettled weather will continue through Labor Day weekend, with increasing chances of rain each day. Increased risk for flooding Sunday.

- 2) Hot and humid conditions expected into the upcoming weekend.

DISCUSSION

KEY MESSAGE 1: Unsettled weather will continue through Labor Day weekend, with increasing chances of rain each day. Increased risk for flooding Sunday.

Today: Expect scattered showers and thunderstorms to return this afternoon, with the greatest coverage residing across southeast Georgia. A plume of deeper low-lvl moisture will continue to spread northward while weak mid-lvl energy shifts into the region. Although the lingering mid-lvl ridge and associated subsidence should limit more widespread convection, the combination of increasing moisture, daytime instability, and convergence along the afternoon sea breeze should be sufficient enough for scattered coverage, especially across southeast Georgia. Coverage will be significantly less across the South Carolina Lowcountry where notably drier air remains thanks to the placement of the mid-lvl ridge.

Saturday through Monday: Another round of mainly isolated to scattered afternoon showers and thunderstorms, though much of Saturday could remain dry. Moisture should continue to increase ahead of an approaching cold front from the north, with the front reaching the area Saturday night into Sunday. Rain chances should increase considerably on Sunday as the front encounters a warm and increasingly moist airmass, providing more forcing for ascent. Numerous showers and thunderstorms are possible, particularly in the afternoon as the front interacts with the sea breeze and peak daytime heating. Locally heavy rainfall will be prevalent with these showers and thunderstorms with convection gradually shifting south on Sunday night as the front begins to move towards northern Florida. Total rainfall amounts Sunday look to fall into the 1-3" range with locally higher amounts. This could lead to at least minor flooding with pockets of flash flooding possible. The corridor of greatest coverage and heaviest rainfall will depend heavily on the eventual frontal position. It's possible unsettled conditions could continue into Labor Day, despite the front being displaced well to the south of region. In addition, it could be quite breezy across the coastline given the possibility of a pinched pressure gradient associated with the inland wedge.

KEY MESSAGE 2: Hot and humid conditions expected into the upcoming weekend.

While the ridge breaks down on Saturday as a trough develops along the East Coast, Saturday continues to look like the hottest day. Ahead of an approaching cold front, compressional heating combined with 850 hPa temperatures 20-22C are expected to push afternoon temperatures into upper 80s/lower 90s inland just inland from the beaches and up into the mid 90s for inland areas. Dewpoints will likely mix out to some degree during peak heating, but look to pool into the upper 70s/near 80 across portions of the coastal corridor along/behind the resultant sea breeze circulation. This could push heat indices into the 108-112 range, especially across portions of the lower South Carolina coast with 103-108 elsewhere. A Heat Advisory may very well be needed for parts of the area, especially the coastal corridor extending from eastern portions of Berkeley County south into Beaufort and Jasper Counties, including parts of the Charleston Metro Area. It looks a bit more marginal for parts of the Georgia coast at this time, including the Savannah Metro ARea. Current data suggest convection ahead of an approaching backdoor cold front will not arrive until after sunset Saturday evening, but some isolated convection could still provide some pockets of relief from the heat. Convection with the backdoor cold front will likely keep conditions below Heat Advisory thresholds for Sunday.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

04/12z TAFs: KCHS/KJZI/KSAV: VFR will prevail for much of the 12z TAF cycle.

Extended Aviation Outlook: Chances for flight restrictions with showers/tstms increase at all terminals this weekend prior to and during a passing cold front. Periodic flight restrictions are more likely Sunday/Monday near and behind a backdoor cold front given greater coverage of rainfall. Breezy conditions could also develop at all terminals as a wedge takes shape.

MARINE

Through Tonight: There are no concerns. South to southeast winds will veer more to the southwest tonight as the low-level flow begins to feel the influence of an approaching cold front. Speeds will average 10 kt or less with seas 2-3 ft.

Saturday through Wednesday: The main concern centers on a likely tightening of the pressure gradient associated with wedge of high pressure that will develop Sunday night into Monday in the wake of backdoor cold front. Expect northeast winds as high as 20-25 kt to occur, especially across the South Carolina coastal waters and 15-20 kt with gusts to 25 kt across the Georgia waters as well as the Charleston Harbor. Seas could reach as high as 3-5 ft, but could end up as high as 6 ft at times, especially across the South Santee-Edisto Beach nearshore and offshore legs. A Small Craft Advisory could be needed for some waters for Monday into Monday night, possibly extending into Tuesday.

Coastal Flooding: Elevated high tides return Sunday afternoon during the lunar Perigee (09/06), and linger throughout the week until after the new moon (09/11). With astronomical high tides ranging from 6.30-6.55 ft MLLW in the Charleston Harbor throughout the week, tidal departures of 0.45-0.70 ft would result in minor coastal flooding. A high pressure wedge may set up along the east coast next week, which could be capable of producing the tidal departures leading to coastal flooding, especially along the coasts of Charleston and Colleton Counties. For the rest of the coast from Beaufort County, SC, south to McIntosh County, GA, tidal departures would need to be in excess of 1 ft, so coastal flooding appears unlikely at this time. Should the gradient pinch a bit more than expected with the inland high pressure wedge, then the risk for flooding could increase.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.