Hanahan, SC 29410 Weather

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.

Aviation

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

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