textproduct: Charleston

WHAT HAS CHANGED

The Aviation section was updated for the 12z TAFs.

KEY MESSAGES

- 1) Below normal temperatures will continue this week as high pressure prevails and a powerful nor'easter gradually pulls away from the Mid-Atlantic coast.

- 2) Risk for minor coastal flooding through Thursday along coastal areas of Charleston and Colleton Counties. The highest astronomical tides of 2026, combined with near gale force northeast winds, will bring a multi-day coastal flooding and coastal hazards threat Friday into early next week.

DISCUSSION

KEY MESSAGE 1: Below normal temperatures will continue this week as high pressure prevails and a powerful nor'easter gradually pulls away from the Mid-Atlantic coast.

Through Daybreak: The boundary layer has mostly decoupled inland away from the coastal corridor with calm to light/variable winds being reported across most observation platforms. Strong radiational cooling is in progress with clear skies, calm/light winds and a very dry airmass in place. A small patch of cirrostratus associated with a passing shortwave is moving across parts of the Charleston Tri-County, but no meaningful impacts to temperature have been observed so far. 21/05z temperatures were running about 3-7 degrees colder than the 21/01z NBM, which is not surprising given NBM's well documented warm bias in radiational cooling regimes. Early morning lows were adjusted closer to a blend of the H3R and RAP which yields mid-upper 40s inland to the upper 50s/near 60 at the beaches.

Today and Tonight: Large high pressure will maintain its influence across the region through tonight. Other than a few patches of thin high clouds moving through, mostly clear skies will prevail. Low-level thickness schemes support highs in the mid-upper 70s, which is pretty much in line with the various guidance packages. The 21/01z NBM looks a tad too cool based on highs observed over the past several afternoons and temperatures at or just a degree or so above the third quartile in the interquartile range (IQR) were favored based on a blend of the latest high-res guidance.

The boundary layer will decouple quickly this evening resulting in another round of calm/light winds. These winds combined with ongoing clear skies and a continued dry airmass will support strong radiational cooling. The NBM low temperature forecast again looks too warm given how strong radiative processes will be. Lows were heavily adjusted down as a result with another blend closer to the H3R and RAP favored. Lows will range from the lower-mid 40s inland to the upper 50s at the beaches. Some spotty upper 30s can not be ruled out, especially in some of the typical colder spots such as the Francis Marion National Forest.

Thursday: A nor'easter will be located well off the Northeast U.S. coast in the morning, while High pressure will be north of the Great Lakes region, with it's periphery stretching well into the Southeast U.S. The nor'easter will quickly accelerate away during the day, followed by the periphery of the High building southwards into our region. This will bring our area dry conditions with sunny skies. High temperatures are forecasted to be in the middle to maybe upper 70s. However, the dry conditions, clear skies, and light to calm winds at night will cause decent radiational cooling. This will lead to low temperatures that are several degrees below overnight.

Friday through Sunday: High pressure will strengthen over the Mid- Atlantic States Friday while a coastal trough develops along the Southeast U.S. coast, persisting through the weekend. This will cause NE winds to increase and become gusty, especially closer to the coast. While the High is expected to prevail and keep it dry, there is the potential some showers could make a run for the immediate coast before dissipating. These details will get refined in future forecast. Otherwise, temperatures may be several degrees below normal.

KEY MESSAGE 2: Risk for minor coastal flooding through Thursday along coastal areas of Charleston and Colleton Counties. The highest astronomical tides of 2026, combined with near gale force northeast winds, will bring a multi-day coastal flooding and coastal hazards threat Friday into early next week.

Tide levels in the Charleston Harbor are expected to peak near 7.0 ft MLLW (minor) during the late afternoon/early evening high tide both today and again Thursday.

Tidal departures will begin to increase as northeast winds strengthen along the coast on Saturday. Minor to moderate coastal flooding is possible for Charleston and coastal Colleton counties Saturday evening. Winds are forecast to strengthen to near gale force on Sunday. Moderate to major coastal flooding is possible for Charleston and Colleton counties, with moderate coastal flooding possible along the southern SC and GA coastlines.

The Perigean spring or King Tides will begin this weekend and continue into early next week, the highest astronomical tides of the year will occur Tuesday and Wednesday mornings. In fact, the morning high in the Charleston Harbor will see astronomical high tide values near 6.9 ft MLLW, just 0.1 ft below flood stage. Ongoing gusty northeast winds and elevated tidal departures may lead to coastal flooding for much of next week, most likely during the morning high tide cycle. Fortunately, no measurable rainfall is expected this weekend into early next week.

In addition to coastal flooding, there is an increased risk for a number of coastal hazards including high surf, beach erosion, strong rip currents and breezy to windy conditions.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

21/12z TAFs: KCHS/KJZI/KSAV: VFR through 22/12z.

Extended Aviation Outlook: Gusty northeast winds upwards of 25 kt are expected this weekend.

MARINE

Through Tonight: Conditions are steadily improving across the marine area early this morning. Both wind and sea observations from area buoys indicate conditions have dropped below Small Craft Advisory levels across the nearshore waters and the advisories have been cancelled early. Seas of 3-5 ft across the nearshore waters will subside to 2-4 ft this afternoon and tonight. For the offshore waters, 5-7 ft seas this morning will subside to 4-6 ft overnight. A Small Craft Advisory remains in effect for the Georgia offshore leg. Overall, north/northeast winds of 15-20 kt will prevail across the waters this morning and will slowly diminish to 10-15 kt through the day and into the overnight hours.

Thursday: A nor'easter will be located well off the Northeast U.S. coast in the morning, while High pressure will be north of the Great Lakes region, with it's periphery stretching well into the Southeast U.S. The nor'easter will quickly accelerate away during the day, followed by the periphery of the High building southwards into our region. Expect NE winds during the day and into the evening, then gradually increasing overnight. Lingering 6+ ft seas will cause the Small Craft Advisory for the 20-60 nm GA waters to remain in effect.

Friday through Sunday: High pressure will strengthen over the Mid- Atlantic States Friday while a coastal trough develops along the Southeast U.S. coast, persisting through the weekend. The interaction between these two features will cause marine conditions to rapidly deteriorate Friday. Winds and seas will substantially increase, first necessitating a period of Small Craft Advisories on Friday (including the Charleston Harbor), and then Gale headlines likely for all of our Atlantic waters Friday night into the weekend. Models hint that strong gale conditions are possible, so more significant refinements will be needed for the weekend portion of the wind and wave forecast.

Rip Currents: Today: Lingering long period swell directed into the Georgia will support a moderate risk for rip currents through tonight from Tybee Island to Sapelo Island.

Thursday: There is a Moderate Risk for our GA beaches.

Friday through Sunday: The combination of gales developing in the coastal waters and building seas will lead to an elevated risk of rip currents at all of our beaches.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 6 AM EDT Monday for AMZ384.