textproduct: Charleston

WHAT HAS CHANGED

Aviation updated to represent the 12Z aviation forecast.

KEY MESSAGES

- 1) A significant, multi-day coastal flooding event is expected this weekend through at least the middle of next week.

- 2) Strong northeast flow this weekend and into early next week will result in several hazards including gusty lake winds, rip currents, high surf, and beach erosion.

- 3) Dry conditions and below normal temperatures will continue through early next week before gradually warming up by the end of the week.

DISCUSSION

KEY MESSAGE 1: A significant multi-day coastal flooding event is expected this weekend through at least the middle of next week.

Astronomical tides will continue to rise through the remainder of the weekend and into next week due to the upcoming full moon (10/26) and the lunar perigee (10/28). Large tidal departures are already ongoing, and with an extended period of strong northeast flow this weekend and into next week, these departures will increase in magnitude. The combination of the highest astronomical tides of the year and persistent strong northeast flow will result in a multi-day moderate to major coastal flooding event for the entire southeast GA/SC coast.

Sunday Morning: Tide levels at the Charleston Harbor are forecast to reach 7.9-8.1 ft MLLW, resulting in a Coastal Flood Warning for Charleston and coastal Colleton. In addition, at these tide levels, up to half a foot of saltwater inundation will be possible for tidal Berkeley county, resulting in a Coastal Flood Advisory. Lastly, a Coastal Flood Advisory has been issued for Fort Pulaski as well, from Beaufort County in SC to McIntosh County in GA, with forecast values of 10.0-10.2 ft MLLW. Current departures are running a little behind forecast; however, winds offshore are expected to increase throughout the morning as we approach high tide and much like yesterday morning we should see things quickly increase through the morning.

Sunday Evening: Tide levels at the Charleston Harbor are forecast to reach 7.4-7.6 ft MLLW, whereas at Fort Pulaski the tide is expected to reach 9.6-9.8 ft MLLW. Coastal flood advisories will most likely be needed.

Next Week: The highest water levels are expected to occur with the Monday, Tuesday, and Wednesday morning high tide cycles. During these cycles, confidence is increasing that Charleston will exceed major flood stage (8.0 ft MLLW) and Fort Pulaski will exceed moderate flood stage (10.0 ft MLLW). There is even concern that Fort Pulaski could reach or exceed its major flood stage (10.5 ft MLLW), which has never happened in its history (records begin in 1935) outside of a tropical system. The one thing keeping us from considering major flooding at Fort Pulaski outside of climatology is that the winds offshore should relax some heading into early next week. While astronomical tides will be running high, the relaxed wind field will likely not support as high departures and without any other considerations for increased departures such as rainfall, there is not enough support for us to feel we can push past the climatological normal. Nonetheless, Coastal flooding will likely occur with both the morning and evening high cycles for several days, though the evening tide will be the lower of the two. Coastal Flood Advisories will definitely be needed, and Coastal Flood Watches/Warnings are very likely for some or all of the coast from Sunday through Wednesday.

KEY MESSAGE 2: Strong northeast flow will result in several hazards including gusty lake winds, rip currents, high surf, and beach erosion.

Rip Currents: Strong northeast winds, increasing long-period swell and wave action will continue to support dangerous rip currents along all SC/GA beaches. A High Risk for rip currents is in place for all beaches Sunday and Monday. An enhanced risk of rip currents will likely continue through the rest of the week.

High Surf/Beach Erosion: Breaking wave heights will peak this evening between 4 and 6 ft along area beaches. A High Surf Advisory remains in effect for the entire Southeast SC/GA coast into Monday, when breakers should subside below 5 ft. Another round of high surf conditions are possible mid-week as the pattern holds, although appears to fall just short of criteria along the SC/GA coast at this time. Additionally, the combination of elevated tides, increased wave action, and persistent gusty northeast winds will likely produce beach erosion, with the most significant erosion occurring around the high tide cycles Sunday and Monday.

Lake Winds: Gusty winds up to 25 kt early this morning across Lake Moultrie will decrease quickly through late morning as the boundary layer decouples over the relatively cool lake waters. After sunset Sunday, winds will briefly ramp up once again as cold air advects over the warmer lake waters, triggering strong vertical mixing and tapping into 40 kt gusts aloft. An additional Lake Wind Advisory could be needed, mainly between the hours of 8 PM Sunday and 4 AM Monday when gusts 25-30 kt would be possible. Furthermore, the combination of steady northeast winds and 2-3 ft waves could yield minor lakeshore erosion along the southwest side of the lake along with some overwash. This includes areas from roughly Pinopolis to Blacks Camp near Cross.

KEY MESSAGE 3: Dry conditions and below normal temperatures will continue through early next week before gradually warming up by the end of the week.

A rather persistent synoptic pattern is expected through the next week, with upper level ridging over the northern Gulf Coast and an upper trough lingering around the Bahamas. At the surface, high pressure centered over New England will dominate through mid-week allowing for a wedge to remain in place across the Carolinas. Temperatures through the remainder of the weekend and into early next week should remain below normal with the cooler air trapped within the wedge. The wedge of high pressure will weaken slightly mid-week, with temperatures returning to near normal by the end of the week as a result. The forecast remains rain-free through the week.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Northeasterly winds will slowly increase after sunrise. Areas well away from the coast are expected to see gusts of 20-25 knots, while those along the coast will be closer to 30 knots.

Extended Aviation Outlook: Breezy north-northeast winds are expected at KCHS/KJZI/KSAV daily through the week. There are no other high confidence concerns.

MARINE

Sunday through Monday: High pressure will continue to strengthen across the Mid-Atlantic while low pressure organizes near the Bahamas Sunday. This setup favors a sharp pinched pressure gradient across the local marine area. Gale Warnings remain in effect for all waters outside of the Charleston Harbor. Gale-force gusts will persist across both nearshore and offshore legs into Monday, lingering longest over the Georgia outer waters (20-60 nm). The Charleston Harbor will see northeast gusts of 25 to 30 kt and waves of 2 to 3 ft through Sunday night, and a Small Craft Advisory remains in effect there.

Tuesday through Friday: Winds and seas will begin a slight downward trend Monday night into Tuesday. However, a prevailing tight gradient between inland high pressure and an offshore low will maintain elevated winds and seas through the period. There is a slight surge Wednesday evening when brief gales return to the Georgia waters from 0-60 nm. However, at a minimum, Small Craft Advisory level winds and elevated seas are expected to continue across the coastal waters, outside of the Charleston Harbor, through the rest of the week.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents through this evening for GAZ217-219-239- 241. High Surf Advisory until 5 PM EDT Monday for GAZ217-219-239- 241. Coastal Flood Advisory until 10 AM EDT this morning for GAZ217- 219-239-241. SC...High Risk for Rip Currents through this evening for SCZ148>151. High Surf Advisory until 5 PM EDT Monday for SCZ148>151. Coastal Flood Advisory until 10 AM EDT this morning for SCZ148- 151-152. Lake Wind Advisory until 11 AM EDT this morning for SCZ045. Coastal Flood Warning until 11 AM EDT this morning for SCZ149- 150. MARINE...Small Craft Advisory until 5 AM EDT Monday for AMZ340. Gale Warning until 5 AM EDT Monday for AMZ360-362-364. Gale Warning until 2 PM EDT Monday for AMZ380-382. Gale Warning until 2 AM EDT Tuesday for AMZ384.