textproduct: Charleston

WHAT HAS CHANGED

Minor changes to Key Message 1.

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.

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. 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 this weekend and into early next week 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 this weekend. A High Risk for rip currents is in place for all beaches this afternoon through Sunday, and will likely persist for all beaches again on Monday. An enhanced period of rip currents will continue into the middle of next week.

High Surf/Beach Erosion: Breaking wave heights will increase late afternoon and evening, reaching 5-6 ft or possibly higher along area beaches, likely largest along the GA coast. A High Surf Advisory remains in effect for the entire Southeast SC/GA coast into Monday. The combination of elevated tides, increased wave action and the persistent/gusty northeast winds will likely produce beach erosion as well, with the most significant impacts occurring around high tide cycles this weekend into Monday. Another round of high surf is possible mid-week as the pattern holds in place, although appears to fall just short of criteria along the SC/GA coast at this time.

Lake Winds: Northeast winds will steadily increase across Lake Moultrie late day into early evening, then likely persist into late morning Sunday given water temps in the upper 60s and cold air advection aloft promoting low-lvl mixing into 1000mb geostrophic flow around 40 kt. A Lake Wind Advisory remains in effect this evening into late morning Sunday for northeast winds gusting upwards to 25-30 kt at times. Furthermore, the combination of 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.

Little change in the 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 will dominate, centered over New England through mid-week. Temperatures through the remainder of the weekend and into early next week will be below normal. 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 /01Z SUNDAY THROUGH THURSDAY/

Northeasterly winds will remain gusty into the overnight hours, increasing after sunrise to become breezy again. 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: VFR conditions are expected at CHS/JZI/SAV through the middle of next week. However, breezy/gusty north-northeast winds are likely Sunday afternoon (up to 25-30 kt).

MARINE

Saturday through Monday: High pressure continues to strengthen across the Mid-Atlantic states while low pressure becomes more organized north of the Bahamas through the weekend. The setup favors a strong pressure gradient across local waters, supporting the continuation of Gale Warnings across nearshore/offshore waters into Monday, but lingering longest across offshore Georgia waters into Monday night. Gusts up to 40-45 kt are possible, strongest across southern SC and GA offshore waters. A Small Craft Advisory will also continue in the Charleston Harbor (gusts 25-30 kt and seas 1-2 ft) through the weekend, but likely ending prior to daybreak Monday.

Tuesday through Thursday: Winds/seas will gradually trend lower heading into Tuesday, but a tight gradient between inland high pressure and persistent low pressure centered well offshore will likely maintain elevated winds and seas through late week. Solid Small Craft Advisory level conditions, north-northeast winds 25-30 kt with seas 5-8 ft nearshore and 7-10 ft offshore (largest across GA waters), will be common through the period and could eventually lead to another episode of high surf (5 ft breakers) along the beaches mid-week given the persistent onshore wind and long duration fetch. The GA coast appears to be more at risk should this scenario develop.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents through Sunday evening for GAZ217-219- 239-241. High Surf Advisory until 5 PM EDT Monday for GAZ217-219-239- 241. Coastal Flood Advisory from 5 AM to 10 AM EDT Sunday for GAZ217-219-239-241. SC...High Risk for Rip Currents through Sunday evening for SCZ148>151. High Surf Advisory until 5 PM EDT Monday for SCZ148>151. Coastal Flood Advisory from 5 AM to 10 AM EDT Sunday for SCZ148-151. Lake Wind Advisory until 11 AM EDT Sunday for SCZ045. Coastal Flood Warning from 4 AM to 11 AM EDT Sunday for SCZ149- 150. Coastal Flood Advisory from 6 AM to 10 AM EDT Sunday for SCZ152. 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.