Charleston Weather

Every figure on this page comes from one source: the 1991–2020 climate normals for Charleston International Airport, NOAA station USW00013880, which is the official climate station for the city. The airport is about eleven miles inland from the Battery, so the peninsula runs a degree or two cooler on a July afternoon and a degree or two warmer on a January night. The shape of the year is the same.

Charleston has two climates rather than four seasons. From late October to early May the air is dry and afternoons sit in the 60s and 70s. From June to mid-September the air is wet, the nights stop cooling, and rain arrives in the afternoon on nearly every other day. March, May and October are the hinges between them, and they move fast: the normal high on October 1 is 82.0°F and on October 31 it is 73.6°F, with the overnight low falling twelve degrees over the same four weeks.

That table is the climate. It is not a recommendation. If the question you actually came with is which month should you pick, that guide handles crowds, prices, the event calendar and the trade-offs between them, and it is a different decision from this one.

The humidity number you are shown is the wrong one

Relative humidity is what weather apps display, and it is close to useless for deciding what to wear. It measures how full the air is relative to what it could hold at that temperature, so it falls as the day warms even when nothing about the air has changed. Dew point measures the water itself, and it is the number that tracks how the air feels on your skin.

Compare mid-August and mid-October in Charleston, using NOAA's hourly normals. At 6 a.m. on August 15 the normal is 75°F with a 72.5°F dew point, which works out to 92 percent relative humidity. At 6 a.m. on October 15 it is 61°F with a 58°F dew point: 90 percent. Two points apart, and one of them is a sauna.

The afternoon flips the ranking without helping. At 3 p.m. on August 15 the normals read 88°F and 60 percent humidity. On October 15, 76.5°F and 53 percent. Seven points apart, for two afternoons that have nothing in common.

The dew point tells the truth in both cases. The National Weather Service comfort scale puts 55°F and below in the pleasant range, 60 to 65°F at noticeably sticky, and 70°F and above at oppressive. Charleston's monthly average dew points, from the hourly normals, are 38.7°F in January, 40.9 in February, 45.8 in March, 53.5 in April, 62.0 in May, 69.6 in June, 72.9 in July, 72.6 in August, 67.9 in September, 58.5 in October, 48.3 in November and 42.6 in December.

Four months sit at or above the oppressive line. What makes July and August here distinctive is not the daytime peak but the fact that the dew point never comes down. On August 15 the hourly normal holds between 72.3°F and 73.6°F for all twenty-four hours of the day. There is no cool hour to walk in, not at 6 a.m. and not at 10 p.m. Mid-October runs 57.5°F to 60.2°F across the same twenty-four hours.

Summer rain and winter rain are different weather

Charleston gets 52.51 inches a year, well ahead of Seattle's 39.34, on 113.7 days with at least a hundredth of an inch and 74.4 days with a tenth or more. But 25.79 of those inches, 49 percent of the year's total, fall in the four months from June through September.

They also fall differently. In July, 43 percent of days record measurable rain, so it feels as if it rains constantly. It does not rain for long. Using hourly airport observations from the summers of 2016 through 2020, 74 percent of June-to-September rain events lasted two hours or less, and 59 percent of all summer rainfall arrived between noon and 8 p.m. The wettest single hour of the average summer day is 4 p.m. That is sea-breeze convection: the land heats through the morning, air rises, a thunderstorm builds in the afternoon and it is gone before dinner.

Winter rain comes from fronts, and fronts do not keep office hours. Across the same five years, 45 percent of December-to-February rainfall fell between midnight and 9 a.m., and 19 percent of winter rain events ran five hours or longer, about double the summer share. A February rain day is the kind that ruins a plan. A July rain day usually costs you two hours in the middle of the afternoon, which is when you wanted to be indoors anyway.

The cloud record says the same thing from another direction. NOAA's hourly normals log a clear sky for 45 percent of November hours, the highest of any month, and overcast for 28 percent of February hours, also the highest of any month. July, the second-wettest month on the calendar, is overcast only 10 percent of the time. Summer in Charleston is not grey. It is blue with a storm cut into the middle of it. If one of those lands on your afternoon, rainy day Charleston is the indoor list.

Heat and cold, counted in days rather than averages

Averages flatten the part you have to plan around. Charleston averages 64.3 days a year at or above 90°F, and 52.1 of them land in June, July and August. Either side of that block a 90°F day is unusual: April averages 0.6 and October 0.5. Real extreme heat is rare, at 0.8 days a year at or above 100°F. What the city does have is length. The airport reaches 80°F or higher on 178.3 days in a normal year, so roughly half the calendar is short-sleeve weather.

The other summer figure worth knowing is the diurnal range, the gap between a day's high and its low. In March it is 22.8°F. In August it is 16.7°F. Charleston summer nights do not cool off, which is why an 8 p.m. walk in August is not the relief it would be in a drier climate, and why the mid-October version of the same walk feels like a different city.

Winter is short, mild and occasionally sharp. A normal year has 22.4 nights below freezing, concentrated in January (9.1) and December (6.0), and 1.1 nights below 20°F. Daytime freezing effectively does not happen: 0.1 days a year fail to reach 32°F. The cold visitors remember is wind rather than temperature, coming off the water at the Battery on a 45°F evening.

Water temperature by season

Air temperature does not decide whether you swim. Water temperature does, and it lags the air by about a month at each end of the year. These are monthly averages from the NOAA gauge in Charleston Harbor, station 8665530, over 2022 through 2025.

Winter is genuinely cold: about 53°F in January and February, 56°F in December. That is wetsuit water and cold enough to be dangerous if you go in unplanned. Spring climbs quickly, 61°F in March, 69°F in April, 76°F in May, so the swimmable line gets crossed in the first half of May. Summer peaks at 86°F in July and 84°F in August, which is bath-warm rather than refreshing. Autumn holds on: 80°F in September, 72°F in October, 65°F in November.

The harbor gauge sits at the Customs House and reads a degree or two off the surf at Folly or Isle of Palms, but the seasonal shape is what matters. On water temperature alone, September is the best swimming month of the Charleston year. Our Charleston beaches guide covers which beach to pick and where to park at it.

Snow: 0.3 inches a year, and two exceptions

The annual snowfall normal for Charleston is 0.3 inches, all of it in January (0.2) and February (0.1). Measurable snow, a tenth of an inch or more, falls on 0.2 days in a normal year, which is about one winter in five.

The record is specific. The largest snowfall in the station's history, which runs back to 1937, came over December 22–24, 1989: 1.5 inches on the 22nd, 6.0 on the 23rd and 0.5 on the 24th, for 8.0 inches and a snow depth of 8 inches on Christmas Eve. The low on Christmas morning was 14°F. No storm since has come close. The next-largest daily totals in the record are 5.4 inches on February 10, 1973 and 5.3 inches on January 3, 2018.

The recent one is January 21–22, 2025, when 2.5 inches fell at the airport across two days and left a 3-inch depth. That was enough to close bridges, schools and most of the city for two days, because a place that averages a third of an inch a year does not own snowplows. If you are travelling in January and your flight matters, that is the argument for a refundable booking, not the 0.3-inch normal.

Hurricane season, briefly

Atlantic hurricane season runs June 1 to November 30 and peaks on September 10, per the National Hurricane Center. Those are basin-wide dates rather than Charleston's odds, and the two are not the same thing: the chance a storm affects one specific four-day trip is in the low single digits even at the statistical peak. Charleston in September carries the per-trip numbers worked out from NOAA's HURDAT2 track record, along with what a watch and a warning actually oblige you to do. The short practical version for any trip between mid-August and mid-October: book a refundable rate, and buy travel insurance in the same week you book, because insurers treat a system as foreseeable the moment it is named.

Rain plus tide is the flooding that affects a trip

Charleston floods far more often from tides than from storms. The peninsula is low and flat, its storm drains empty into the harbor, and when the tide is up they cannot empty at all. Minor flood stage at the harbor gauge is 7.0 feet MLLW. The gauge topped that mark on more than 50 days in each of 2024 and 2025, close to one a week. Note that NOAA's official high-tide-flooding count, which uses a stricter derived threshold, is far lower at seven days a year, so figures for Charleston flooding vary hugely depending on which threshold a source uses.

On those days a heavy shower has nowhere to go, and streets on the lower peninsula hold water for an hour or two either side of high tide. It is inconvenient rather than dangerous, and it drains as the tide falls, but it will soak your shoes. NOAA publishes free tide predictions for the harbor. If the day's high is near seven feet and rain is in the forecast, move the Battery walk to a different hour rather than cancelling it.

What to pack, by season

Summer, June through September. The lightest clothes you own, in fabrics that dry. Two pairs of shoes, because one of them will be wet. Sunscreen and a hat matter more than a rain jacket, since the rain is warm and brief and a small umbrella beats a coat. Bring one light layer anyway, for restaurants that set the air conditioning to arctic.

Spring and autumn, March through May and October into November. This is the layering climate. A 22-degree diurnal range means the 7 a.m. and 3 p.m. versions of the same day are different seasons. Long sleeves in the morning, short sleeves by lunch, a jacket for the evening.

Winter, December through February. A proper coat rather than a fleece, because the wind off the water is the entire story, plus something for your head on an evening walk. Rain gear matters more than warm gear here: winter is when the all-day rain happens. Leave the snow boots at home.

Year-round, bring comfortable shoes with a real sole. The historic district is brick, bluestone and buckled slate, and it punishes thin soles in any forecast. The rest of the practical checklist is in plan your trip.