Avg High
London in September
Avg Low
Rain
Daylight
13h
What to expect
London is in early autumn during September, a shoulder-season stretch where conditions can nudge warmer or cooler week to week. It generally feels mild and comfortable, and a gentle drop-off once the sun goes down. Conditions tend to feel steady, which makes planning simple. You get a comfortable daylight window for day trips and sightseeing.
September in context
How it compares to the rest of the year in London.
Hottest (avg)
#4 / 12
Wettest (avg)
#9 / 12
Daylight Hours
#6 / 12
Windiest (avg)
#9 / 12
Highest UV
#6 / 12
Most Humid
#7 / 12
Monthly climate breakdown
Temperature
- Daytime high
-
- Nighttime low
-
- Feels like (avg)
-
Sunshine
- Daylight hours
- 12.6 h
- UV index (max)
- 5
- Typical sun hours
- 05:36 - 18:14
Rain & Snow
- Total rain
-
- Rainy days
- 12 days
- Cloud cover (avg)
- 66%
Humidity & Wind
- Humidity (avg)
- 78%
- Wind (avg)
-
- Wind (max gusts)
-
Daily climate explorer
Day 15 selected for September. Typical high 18.5°C and low 10.2°C.
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 11% of days (3.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.3 days / month
~11% of days
Why this matters
- Expected days 3.3 days / month
- Probability ~11% of days
- Intensity Up to ~19mm (P95)
Washout conditions are possible on ~3 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 6% of days (1.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.7 days / month
~6% of days
Why this matters
- Expected days 1.7 days / month
- Probability ~6% of days
- Intensity Up to ~79km/h (P95)
Strong gusts are possible on ~2 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Moderate
Rain disruption Measures: Likely rain disruption days. Observed about 12% of days (3.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.5 days / month
~12% of days
Why this matters
- Expected days 3.5 days / month
- Probability ~12% of days
- Intensity Up to ~19mm (P95)
Rain disruption risk appears on ~4 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cold Moderate
Cold feels-like nights Measures: Cold feels-like nights (min <=5C). Observed about 9% of days (2.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
2.7 days / month
~9% of days
Why this matters
- Expected days 2.7 days / month
- Probability ~9% of days
- Intensity Up to ~5°C (P95)
Cold feels-like nights are possible on ~3 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Visibility Minor
Fog-likely signal Measures: Fog-likely visibility proxy. Observed about 2% of days (0.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.6 days / month
~2% of days
Why this matters
- Expected days 0.6 days / month
- Probability ~2% of days
- Intensity Up to ~94% (P95)
Fog-likely conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Show all disruptions (14 more)
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 0.6 days/month in September. Historical risk signal only, not a day-by-day forecast.
0.6 days / month
Probability unavailable
Why this matters
- Expected days 0.6 days / month
- Probability —
- Intensity Up to ~34mm (P95)
Multi-day washout runs are 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 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.4 days / month
~1% of days
Why this matters
- Expected days 0.4 days / month
- Probability ~1% of days
- Intensity Up to ~75km/h (P95)
Stormy conditions are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Moderate
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 4% of days (1.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.1 days / month
~4% of days
Why this matters
- Expected days 1.1 days / month
- Probability ~4% of days
- Intensity Up to ~30mm (P95)
Heavy rain is possible on ~1 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 63% of days (19.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
19.0 days / month
~63% of days
Why this matters
- Expected days 19.0 days / month
- Probability ~63% of days
- Intensity Up to ~99% (P95)
Cloudy skies are possible on ~19 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 52% of days (15.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
15.6 days / month
~52% of days
Why this matters
- Expected days 15.6 days / month
- Probability ~52% of days
- Intensity Up to ~12mm (P95)
Measurable rain is possible on ~16 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 42% of days (12.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
12.6 days / month
~42% of days
Why this matters
- Expected days 12.6 days / month
- Probability ~42% of days
- Intensity Up to ~91% (P95)
High humidity is possible on ~13 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 41% of days (12.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
12.2 days / month
~41% of days
Why this matters
- Expected days 12.2 days / month
- Probability ~41% of days
- Intensity Up to ~69km/h (P95)
Gusty conditions are possible on ~12 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 37% of days (11.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
11.1 days / month
~37% of days
Why this matters
- Expected days 11.1 days / month
- Probability ~37% of days
- Intensity Up to ~17h (P95)
Several rainy hours 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 36% of days (10.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
10.8 days / month
~36% of days
Why this matters
- Expected days 10.8 days / month
- Probability ~36% of days
- Intensity Up to ~99% (P95)
Mostly cloudy skies are possible on ~11 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 22% of days (6.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
6.5 days / month
~22% of days
Why this matters
- Expected days 6.5 days / month
- Probability ~22% of days
- Intensity Up to ~18h (P95)
Wet-most-of-day conditions are possible on ~7 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 12% of days (3.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.5 days / month
~12% of days
Why this matters
- Expected days 3.5 days / month
- Probability ~12% of days
- Intensity Up to ~100% (P95)
Overcast skies are possible on ~3 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 2% of days (0.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.7 days / month
~2% of days
Why this matters
- Expected days 0.7 days / month
- Probability ~2% of days
- Intensity Up to ~31km/h (P95)
Breezy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
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 2% of days (0.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.6 days / month
~2% of days
Why this matters
- Expected days 0.6 days / month
- Probability ~2% of days
- Intensity Up to ~94 (P95)
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.
Cold Minor
Cold nights Measures: Cold nights (min <=5C). Observed about 1% of days (0.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.2 days / month
~1% of days
Why this matters
- Expected days 0.2 days / month
- Probability ~1% of days
- Intensity Up to ~5°C (P95)
Cold nights are possible on ~0 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Frequently asked questions
Is September a good time to visit London?
Typical September days in London reach highs of 19°C (66°F) with nights around 11°C (52°F). It usually feels mild by day and cool after dark. Overall, September sits in the middle of the London climate range.
What are temperatures like in September?
In September, you can usually expect highs of 19°C (66°F) and lows near 11°C (52°F). That means mild days and cool nights, so pack layers you can add or remove.
How much does it rain in September?
Rainfall in September averages 50 mm (2.0 in) across roughly 12 days. Overall it is a quite rainy 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 13 hours of daylight in September. Sunrise is typically around 05:36 and sunset near 18:14. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are moderate (around 5); sunscreen and sunglasses are still a good idea.
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 57 km/h (35 mph). On the ground, it is it can feel quite windy at times, particularly when weather systems move through.