textproduct: Charleston

WHAT HAS CHANGED

Key Message 2 was updated to cancel the Coastal Flood Advisory this morning as tide levels in the Charleston Harbor have dropped below minor flood stage. The Aviation section was updated for the 23/12z TAFs.

KEY MESSAGES

- 1) Dry conditions and below normal temperatures will continue into early next week.

- 2) Multi-day coastal flooding event expected this weekend into next week.

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

DISCUSSION

KEY MESSAGE 1: Dry conditions and below normal temperatures will continue into early next week.

Through Daybreak: Conditions early this morning are the same as the past several. Clear skies, calm winds within a decoupled boundary layer and a resident dry airmass are promoting strong radiational cooling. Hourly temperatures are running a few degrees colder than the 23/01z NBM, which is not surprising given its classic warm bias in strong radiational regimes. Lows were adjusted down from the NBM given current trends and are on track to bottom out in the lower-mid 40s inland to the upper 50s at the beaches. The pressure gradient is forecast to slightly tighten as daybreak approaches which should curtail the radiative processes in some areas, especially east of I-95.

Today and Tonight: There is no change in the surface pattern with strong high pressure prevailing. High temperatures today will run just a bit cooler than Thursday with temperatures aloft forecast to cool slightly as a strong shortwave drops south along the Southeast U.S. coast. Even with the cooler temperatures aloft, full insolation is expected with highs poised to warm into the lower-mid 70s away from the beaches. The pressure gradient will begin to quickly tighten tonight as low pressure begins to organize east of the Southern Bahamas and strong high pressure centered over New England steadily wedges south across the Carolinas and Georgia. This will result in a uptick in winds through the night with breezy conditions developing at the beaches and around the Santee-Cooper lakes. Despite clear skies, it will be an overall warmer night with lows ranging from the upper 40/lower 50s inland to around 60 at the beaches. Some mid 40s could occur, mainly in the Jenkins- Allendale corridor where winds will be the lightest.

Saturday through Thursday: Surface high pressure will extend across the region through late week. Over the weekend, the high will strengthen inland while a coastal trough develops offshore. The air mass will remain quite dry. The pattern will support a rain-free forecast through at least early next week. Despite plenty of sunshine, temperatures will lean on the cooler side of normal. Highs will top out in the lower to mid 70s for the weekend and early next week. Low temperatures will fall into the 40s across many interior locations.

KEY MESSAGE 2: Multi-day coastal flooding event expected this weekend into next week.

Astronomical tides will continue to rise through the weekend and into next week with the upcoming lunar perigee (10/28) and full moon (10/26). With another period of strong northeast flow on the way this weekend into next week, large tidal departures will start to overlap with increasing astronomical tides, providing increased probabilities of seeing a multi-day coastal flooding event for the entire coast.

Today, minor coastal flooding is likely again in the Charleston Harbor with this evening's high tide before conditions deteriorate further heading into the weekend. Another Coastal Flood Advisory may be needed for Charleston and Colleton Counties. Tides should remain below minor flood thresholds at Fort Pulaski for this evening's high tide.

Over the weekend and into the middle of week, the potential for coastal flooding escalates to moderate-to-major levels at Charleston Harbor and minor-to-moderate levels at Fort Pulaski. While the morning high tide will be the dominant peak each day, water levels possibly pushed more than a foot above predicted levels could cause coastal flooding during evening high tides as well. Persistent onshore winds will also prevent water from fully draining during low tide, creating extended periods of elevated water and prolonged inundation. This setup aligns with the highest astronomical tides of 2026 as we approach the full moon on October 26 and lunar perigee on October 28. Astro tides will peak Tuesday and Wednesday at 6.87 ft MLLW in Charleston Harbor and 8.90 ft MLLW at Fort Pulaski before accounting for wind-driven surge. There is an increasing possibility that tides could approach major flood stage at Fort Pulaski Monday morning and trends are being monitored for forecast adjustments.

KEY MESSAGE 3: Strong northeast flow this weekend and into early next week will result in several coastal hazards including rip currents, high surf, and beach erosion.

Rip Currents: Strong northeast winds and increased wave action will support an elevated rip current risk over the weekend and into early next week. A Moderate Risk for rip currents is in place for all beaches today, followed by a High Risk Saturday. An enhanced period of rip currents will likely continue into early next week.

High Surf: Breaking wave heights of 5 ft or higher will be possible and High Surf Advisories could be needed this weekend into early next week. 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 high tide cycles this weekend.

Lake Winds: Gusty northeast winds will pick up across Lake Moultrie Friday night and persist through the weekend. Winds could briefly gust around 25 kt early Saturday morning, but due to the short duration, a Lake Wind Advisory will be withheld for Friday night. Gusts will then decrease by late morning as the boundary layer decouples over the relatively cooler lake waters. After sunset Saturday, the pattern flips and winds will rapidly pick up as cold air advection occurs over the warmer lake waters. This will trigger strong mixing, dragging 30 kt wind gusts down to the lake surface. A Lake Wind Advisory will likely be needed starting Saturday night. The combination of steady northeast winds and 2-3 ft waves could yield lakeshore erosion along the southwest side of the lake along with some overwash. This is includes areas from roughly Pinopolis to Blacks Camp near Cross.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

23/12z TAFs: KCHS/KJZI/KSAV: VFR through 24/12z.

Extended Aviation Outlook: Breezy northerly winds anticipated through Monday morning. Gusts could reach 25-30 kt, especially during the afternoon hours Saturday and Sunday.

MARINE

Today: It will remain relatively quiet across the waters today before conditions deteriorate tonight. Northeast winds will begin to increase to 15-20 kt later this morning and persist into the afternoon in response to a tightening of the pressure gradient. Seas across the Georgia offshore waters have finally dropped below 6 ft and the Small Craft Advisory there was cancelled early. Seas will average 2-4 ft nearshore waters and 4-5 ft offshore waters.

Tonight: Conditions will begin to steadily deteriorate tonight as the pressure gradient between high pressure over New England wedging south and low pressure developing east of the Southern Bahamas steadily tightens. Northeast winds are expected to increase to 20-25 kt with gusts to 30 kt and 25-30 kt with gusts to 35 kt over the offshore waters. Seas will build to 4-6 nearshore and 6-8 ft offshore. A Small Craft Advisory has been posted for all nearshore waters and Charleston Harbor for tonight with a Gale Watch over the offshore waters. A Gale Warning would normally be issued at this time given the onset of frequent gale-force gusts is within 24 hours, but there are some slight timing uncertainties of when these gusts will occur. A Gale Watch was favored over a Gale Warning given this.

Saturday and Sunday: A deepening high pressure wedge to the north will result in deteriorating conditions over the local waters this weekend. Winds will reach their peak Saturday and Sunday evening with solid gale-force conditions across the coastal waters. Prolonged northeast fetch will yield dangerous seas which look to peak Sunday evening at 8-12 ft across the nearshore waters (0-20 nm) and 11-15 ft across the offshore waters (20-60 nm).

Monday through Wednesday: Winds and seas will gradually trend lower Monday afternoon, but at the least, Small Craft Advisory level conditions could persist across local waters outside the Charleston Harbor through the period. Gale conditions could linger over the offshore waters through the entire period as well due to a persistent, tight pressure gradient anchored across the region.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 2 AM Saturday to 6 AM EDT Monday for AMZ340. Small Craft Advisory from 6 PM this evening to 6 AM EDT Saturday for AMZ360-362-364. Gale Watch from Saturday morning through late Sunday night for AMZ360-362-364. Gale Watch from 6 PM EDT this evening through late Monday night for AMZ380-382-384.