Hottest (avg)
#4 / 12
Sits around the middle of the year.
September in context
How it compares to the rest of the year in Charleston.
Wettest (avg)
#3 / 12
Among the wetter months.
Daylight Hours
#6 / 12
Around the yearly average.
Windiest (avg)
#8 / 12
Close to the yearly wind average.
Highest UV
#6 / 12
Near the middle of the yearly UV range.
Most Humid
#3 / 12
Humidity sits on the higher side.
Monthly climate breakdown
A detailed look at the typical climate conditions for September.
Thermal profile
Temperature
Typical daytime high
- Nighttime low
-
- Feels like (avg)
-
Light window
Sunshine
12.4 h
Average daylight
- UV index (max)
- 8
- Typical sun hours
- 06:03 - 18:24
Wet-day pattern
Rain & Snow
Typical rainfall
- Rainy days
- 17 days
- Cloud cover (avg)
- 55%
Air feel
Humidity & Wind
79%
Average humidity
- Wind (avg)
-
- Wind (max gusts)
-
Historical daily baseline
Daily climate explorer
Pick a day to inspect the usual conditions through September in Charleston. Based on a 30-year historical climate baseline, not a forecast.
Primary control
Select a day
Scroll to compare daily conditions. The summary updates with your selection.
Secondary context
Monthly trend
Median daytime highs across the month, with a softer low line.
Median temperatureMedian lowTypical range
Day 15 selected for September. Temperature 28.0°C.
Historical disruption baseline
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Humidity High impact
Muggy days Measures: Muggy days (dew point >=20C). Observed about 66% of days (19.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
19.9 days / month
- Share of days
- ~66% of days
- Upper edge
- Up to ~24°C (P95)
Why this matters
Muggy conditions are possible on ~20 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat High impact
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 40% of days (12.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
12.1 days / month
- Share of days
- ~40% of days
- Upper edge
- Up to ~37°C (P95)
Why this matters
Feels-like heat >=32C is possible on ~12 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Rain High impact
Rain disruption Measures: Likely rain disruption days. Observed about 23% of days (7.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
7.0 days / month
- Share of days
- ~23% of days
- Upper edge
- Up to ~42mm (P95)
Why this matters
Rain disruption risk appears on ~7 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 22% of days (6.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
6.6 days / month
- Share of days
- ~22% of days
- Upper edge
- Up to ~43mm (P95)
Why this matters
Washout conditions are possible on ~7 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 12% of days (3.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
3.5 days / month
- Share of days
- ~12% of days
- Upper edge
- Up to ~61mm (P95)
Why this matters
Heavy rain is possible on ~4 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Heat High impact
Very hot feels-like Measures: Very hot feels-like days (>=35C). Observed about 9% of days (2.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.7 days / month
- Share of days
- ~9% of days
- Upper edge
- Up to ~38°C (P95)
Why this matters
Very hot feels-like conditions are possible on ~3 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Show all disruptions (29 more)
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 1.7 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.7 days / month
- Share of days
- —
- Upper edge
- Up to ~50mm (P95)
Why this matters
Multi-day washout runs are possible on ~2 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Strong gusts Measures: Strong gust days (>=60 km/h). Observed about 4% of days (1.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.2 days / month
- Share of days
- ~4% of days
- Upper edge
- Up to ~123km/h (P95)
Why this matters
Strong gusts are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain High impact
Very heavy rain Measures: Very heavy rain days (>=25mm). Observed about 3% of days (1.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.0 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~139mm (P95)
Why this matters
Very heavy rain is possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Stormy conditions Measures: Storm-impact proxy days. Observed about 3% of days (0.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.8 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~125km/h (P95)
Why this matters
Stormy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Wind High impact
Severe gusts Measures: Severe gust days (>=80 km/h). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~135km/h (P95)
Why this matters
Severe gusts are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Wind High impact
Wind disruption Measures: Disruptive wind days. Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~134km/h (P95)
Why this matters
Disruptive wind is possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain High impact
Extreme rain Measures: Extreme rain days (>=50mm). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~160mm (P95)
Why this matters
Extreme rain is possible on ~0 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Wind disruption run Measures: Multi-day wind disruption runs. Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.1 days / month
- Share of days
- —
- Upper edge
- Up to ~120km/h (P95)
Why this matters
Multi-day disruptive wind runs are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Heat Moderate
Hot days Measures: Hot days (>=30C). Observed about 13% of days (3.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
3.8 days / month
- Share of days
- ~13% of days
- Upper edge
- Up to ~33°C (P95)
Why this matters
Hot days are possible on ~4 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Moderate
Heat stress risk Measures: High heat stress days. Observed about 9% of days (2.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.7 days / month
- Share of days
- ~9% of days
- Upper edge
- Up to ~38°C (P95)
Why this matters
Heat stress is possible on ~3 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Moderate
Feels-like heatwave Measures: Feels-like heatwave runs (>=3 days). Observed about 1.8 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.8 days / month
- Share of days
- —
- Upper edge
- Up to ~37°C (P95)
Why this matters
Feels-like heatwave runs are possible on ~2 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Humidity Moderate
Oppressive humidity Measures: Oppressive humidity days (dew point >=24C). Observed about 5% of days (1.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.6 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~25°C (P95)
Why this matters
Oppressive humidity is possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Visibility Moderate
Fog-likely signal Measures: Fog-likely visibility proxy. Observed about 5% of days (1.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.4 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~95% (P95)
Why this matters
Fog-likely conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
Humid days Measures: Humid days (dew point >=18C). Observed about 81% of days (24.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
24.4 days / month
- Share of days
- ~81% of days
- Upper edge
- Up to ~24°C (P95)
Why this matters
Humid conditions are possible on ~24 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 64% of days (19.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
19.1 days / month
- Share of days
- ~64% of days
- Upper edge
- Up to ~26mm (P95)
Why this matters
Measurable rain is possible on ~19 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Warm nights Measures: Warm nights (min >=22C). Observed about 59% of days (17.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
17.6 days / month
- Share of days
- ~59% of days
- Upper edge
- Up to ~25°C (P95)
Why this matters
Warm nights are possible on ~18 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 55% of days (16.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
16.4 days / month
- Share of days
- ~55% of days
- Upper edge
- Up to ~92% (P95)
Why this matters
High humidity is possible on ~16 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 50% of days (15.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
15.1 days / month
- Share of days
- ~50% of days
- Upper edge
- Up to ~20h (P95)
Why this matters
Several rainy hours are possible on ~15 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 45% of days (13.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
13.5 days / month
- Share of days
- ~45% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Cloudy skies are possible on ~14 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 35% of days (10.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
10.5 days / month
- Share of days
- ~35% of days
- Upper edge
- Up to ~22h (P95)
Why this matters
Wet-most-of-day conditions are possible on ~11 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 28% of days (8.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
8.4 days / month
- Share of days
- ~28% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Mostly cloudy skies are possible on ~8 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 27% of days (8.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
8.1 days / month
- Share of days
- ~27% of days
- Upper edge
- Up to ~76km/h (P95)
Why this matters
Gusty conditions are possible on ~8 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Humidity Minor
Convective risk Measures: Convective storm risk proxy. Observed about 22% of days (6.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
6.7 days / month
- Share of days
- ~22% of days
- Upper edge
- Up to ~24°C (P95)
Why this matters
Convective risk signal appears on ~7 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 13% of days (4.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.0 days / month
- Share of days
- ~13% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Overcast skies are possible on ~4 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Hot nights Measures: Hot nights (min >=25C). Observed about 6% of days (1.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.9 days / month
- Share of days
- ~6% of days
- Upper edge
- Up to ~26°C (P95)
Why this matters
Hot nights are possible on ~2 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Other Minor
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data Measures: Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data. Observed about 5% of days (1.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.4 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~95 (P95)
Why this matters
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data is possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Wind Minor
Breezy days Measures: Breezy days (mean wind >=25 km/h). Observed about 4% of days (1.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.2 days / month
- Share of days
- ~4% of days
- Upper edge
- Up to ~47km/h (P95)
Why this matters
Breezy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Heat Minor
Heatwave run Measures: Heatwave runs (>=3 hot days). Observed about 0.5 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.5 days / month
- Share of days
- —
- Upper edge
- Up to ~33°C (P95)
Why this matters
Heatwave runs are possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Wind Minor
Windy days Measures: Windy days (mean wind >=35 km/h). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~55km/h (P95)
Why this matters
Strong mean winds are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Travel planning FAQ
Frequently asked questions
Quick answers to the weather questions you ask the most.
Is September a good time to visit Charleston?
Typical September days in Charleston reach highs of 28°C (82°F) with nights around 22°C (72°F). It usually feels hot by day and mild after dark. It is among the wetter months, so it is wise to have some indoor backup plans or flexible activities.
What are temperatures like in September?
In September, you can usually expect highs of 28°C (82°F) and lows near 22°C (72°F). That means hot days and mild nights, so pack layers you can add or remove.
How much does it rain in September?
Rainfall in September averages 131 mm (5.2 in) across roughly 17 days. Overall it is a very wet time of year, so a light rain jacket and waterproof shoes are very handy.
How many hours of daylight are there in September?
You can expect about 12 hours of daylight in September. Sunrise is typically around 06:03 and sunset near 18:24. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are often high (around 8). Regular sunscreen and a hat are recommended.
Is it windy in September?
In September, average wind speeds are around 13 km/h (8 mph), with gusts on the windiest days reaching about 50 km/h (31 mph). On the ground, it is it often feels breezy, especially in more exposed spots or along the coast.