textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Scattered showers and thunderstorms are expected across portions of southeast Georgia and southeast South Carolina each day through the remainder of the week.

- 2) Coastal flooding will impact much of the southeast Georgia and southeast South Carolina coast this week. Tide levels will likely peak today and Wednesday.

- 3) There is a High Risk of rip currents along the entire coastline today and Wednesday.

DISCUSSION

KEY MESSAGE 1: Scattered showers and thunderstorms are expected across portions of southeast Georgia and southeast South Carolina each day through the remainder of the week.

Surface high pressure will dominate over the Mid-Atlantic states with low pressure off the Atlantic coast of Florida. The local forecast are will remain sandwiched between these two features through tonight, yielding a northeasterly flow at the surface. With this flow pattern showers over the adjacent Atlantic waters will be funneled towards the coastline through the remainder of the afternoon. Showers and storms are forecast to be progressive, limiting the heavy rainfall threat. However, some pockets of 1 to maybe 2 inches will be possible with any stronger shower. So far this afternoon there has been no thunder with any showers, however with ML CAPE values around 500-1000 J/kg according to SPC mesoanalysis thunder remains a possibility. After waning with nightfall, additional shower and thunderstorm activity is forecast to again develop early Wednesday morning across the coastal waters, making a run for the coastline by daybreak.

Wednesday through Sunday: Aloft, high pressure extending across the Southeast United States through Thursday will gradually retreat off the Atlantic Coast with the approach of h5 shortwave energy this weekend. At the sfc, high pressure centered off the Mid-Atlantic Coast will linger across the Carolinas and Georgia mid-week, while weak coastal troughing slides onshore locally Wednesday into possibly early Thursday, well ahead of a front that likely stalls just north of the area this weekend.

The coastal trough will initially favor scattered to numerous showers/thunderstorms Wednesday, with the bulk of activity occurring across Southeast Georgia and far southern Southeast South Carolina, followed by precip activity running along the I-95 corridor in a more traditional summertime setup on Thursday as weaker low-lvl flow gradually turns more southerly and increases moisture (PWATS 2+ inches) in the vicinity. Shear is rather weak, especially Thursday, but a few stronger thunderstorms remain possible each afternoon given ample instability across the region. By Friday, a notable uptick in h5 vort energy rounding the western periphery of the Atlantic ridge arrives from the south, likely increasing shower/thunderstorm coverage and potentially a risk for localized heavy rainfall and/or minor flooding issues through this weekend. WPC has highlighted the region in a Marginal Risk for excessive rainfall in the Day 4 (Friday) and Day 5 (Saturday) outlooks.

KEY MESSAGE 2: Coastal flooding will impact much of the southeast Georgia and southeast South Carolina coast this week. Tide levels will likely peak today and Wednesday.

Astronomical tide levels will peak during the evening high tide cycle today through Thursday due to the recent lunar perigee (9/6) and the upcoming new moon (9/11). These factors along with the ongoing strong northeast flow event, will combined to produce elevated tide levels and coastal flooding for much of the coast.

Charleston Harbor: Astronomical tides will be right around 6.5 ft MLLW each evening through Thursday. The ongoing northeast flow event has already pushed tidal departures well in excess of 1 ft, and the northeast flow will peak through the day today. For the upcoming evening high tide (~7 pm), there is increasing confidence in moderate coastal flooding (7.5 ft MLLW or higher). Current model guidance suggests that the evening high tide will peak around 7.6-7.8 ft MLLW with even some support for approaching as high as 7.9 ft MLLW. A Coastal Flood Advisory is in effect for Charleston and coastal Colleton counties. For the Wednesday evening high tide, winds will remain out of a conducive direction (ENE) though wind speeds will come down a bit. This should still be enough to maintain large tidal departures and moderate coastal flooding is possible, if not likely. For Thursday, winds will turn more southerly and weaken considerably. Minor coastal flooding remains quite certain, though the potential for moderate coastal flooding will diminish. Then for Friday and into the weekend, we will see the morning high tide cycle become the higher tide of the day with astronomical values around 6.3 ft. Winds will be more south to southwesterly which will bring departures down and make the occurrence of minor flooding less certain.

Fort Pulaski: The best chance to reach the minor coastal flood threshold (9.5 ft MLLW) will likely come with the upcoming evening high tide (~7 pm). Current departures and model guidance suggest that the tide will peak around 9.6-9.8 ft MLLW and a Coastal Flood Advisory is in effect for Beaufort County south including the entire southeast GA coast. Wednesday also looks like a good candidate for minor coastal flooding as winds remain supportive of large tidal departures. Another advisory could be needed. Thereafter, the coastal flooding potential will diminish as winds diminish and become less favorable.

KEY MESSAGE 3: There is a High Risk of rip currents along the entire coastline today and Wednesday.

Breezy northeasterly flow combined with an easterly swell will continue to support a High Risk for rip currents along all Southeast South Carolina and Southeast Georgia beaches through Wednesday. By Thursday, the flow is expected to turn east-southeast and weaken considerably while swell also decreases. However, the setup still calls for some enhanced rip current risk early Thursday before conditions further improve. A Moderate Risk of rip currents is in place along Georgia beaches on Thursday as a result, and could be needed along South Carolina beaches if stronger winds and larger swell linger longer than currently anticipated.

If you are caught in a rip current, stay calm, do not fight the current, and swim parallel to the shoreline to escape it.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Showers will continue to stream inland from the adjacent Atlantic waters through the remainder of the afternoon, especially at KSAV. Some brief moments of MVFR cigs are possible, however impacts are expected to be so limited no restrictive cigs have been included in the 18Z TAFs. KCHS and KJZI could see shower activity again early Wednesday morning, with a PROB30 introduced with the 18Z TAFs.

Extended Aviation Outlook: Flight restrictions are possible with scattered to numerous showers/thunderstorms at CHS/JZI/SAV terminals, mainly during afternoon hours each day through the end of the week.

MARINE

Through Tonight: Northeast flow will dominate across the marine waters today as the region remains within a pinched pressure gradient with high pressure to the north and low pressure to the south. Gusts as high as 25 knots across all marine waters and the Charleston Harbor will be common this afternoon. A Small Craft Advisory remains in effect for these waters. The SCA in the Charleston Harbor will expire at 00Z this evening, with the remainder of the SCAs expiring Wednesday morning.

Wednesday through Saturday: Moderate easterly flow (15-20 kt) on Wednesday will gradually turn more south-southeast and weaken through Wednesday night following a coastal trough shifting onshore. Wind gusts should then remain at or below 15 kt across local waters through late week well ahead of a front stalling north of the area this weekend. Seas will also subside mid-week, likely to below 6 ft Wednesday afternoon, then should continue to subside to 1-3 ft during a weak high pressure pattern through late week.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ217- 219-239-241. Coastal Flood Advisory until 9 PM EDT this evening for GAZ217- 219-239-241. SC...High Risk for Rip Currents until 8 PM EDT this evening for SCZ148>151. Coastal Flood Advisory until 9 PM EDT this evening for SCZ148>151. MARINE...Small Craft Advisory until 8 PM EDT this evening for AMZ340. Small Craft Advisory until 4 AM EDT Wednesday for AMZ360-362- 364. Small Craft Advisory until 11 AM EDT Wednesday for AMZ384.