London weather in September

In September, London sees average daytime highs of 21°C and overnight lows near 11°C, with 86 mm of rain across 9.7 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 24°C in the first days to 19°C by the end. The sky is clear or mostly clear about 36% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is London's 2nd-clearest and 9th-windiest month. For the whole year in context, see London's year-round climate.

Daytime high
21°
4th warmest
Overnight low
11°
9th coldest
Rainfall
86 mm
9.7 wet days
Daylight
12 h 18 min
6:11 AM – 6:28 PM
Cloud cover
55%
2nd clearest
Wind
11 km/h
9th windiest
Solar energy
4.33 kWh/m²
Travel score
6.6
out of 10

London is city in Southwestern Ontario, Canada.

Air quality
Good
PM2.5 7 µg/m³ · 2019
Density
1,004/km²
people per km²
Founded
1826

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 24°C in the first days to 19°C by the end.

A typical September day in London reaches about 21°C in the afternoon and slips back to 11°C overnight — a 10°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 27°C. Set against its neighbours, September runs about 4°C cooler than August and about 7°C warmer than October.

10°20°30°151015202530
Avg high (°C)Avg low (°C)
12414
22414
32414
42413
52313
62313
72313
82313
92313
102312
112212
122212
132212
142212
152211
162111
172111
182111
192111
202110
212010
222010
232010
242010
25199
26199
27199
28199
29189
30189

How September really feels in London

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

London weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan-1° / -8°7211.79.69.20.0
Feb-0° / -9°589.58.210.20.0
Mar / -4°7010.95.711.60.4
Apr12° / 9312.42.213.13.1
May19° / 9812.5014.45.6
Jun24° / 14°10212015.16.5
Jul26° / 16°10011.9014.86.5
Aug25° / 15°8410.6013.86.8
Sep21° / 11°869.7012.36.6
Oct14° / 8611.80.210.84.1
Nov / 7711.13.99.51.0
Dec / -5°6811.28.18.90.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 18% of September, with mostly cloudy or overcast conditions the remaining 47%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15644
25644
35644
45743
55743
65743
75644
85644
95644
105545
115545
125446
135446
145446
155347
165347
175347
185347
195248
205248
215248
225149
235149
245050
255050
265050
274852
284852
294852
304852

Chance of precipitation in September

Any precipitation

London gets around 86 mm of rain over 9.7 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 33% and peaks near 37% on the wettest days.

0%10%20%30%40%50%151015202530
Rain chance (%)
132
232
332
433
533
633
733
833
933
1032
1132
1232
1332
1431
1531
1631
1731
1830
1930
2031
2131
2232
2332
2433
2534
2635
2736
2836
2937
3037

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 57% of days. Sticky, muggy-or-worse air turns up on roughly 9% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1352719172
2372718162
3382617162
4402617152
5412617142
6432616132
7442516122
8462516122
9472516111
10492416101
11502415101
1252231591
1353231581
1453231581
1556221480
1657221470
1759211370
1861201360
1963191260
2064181260
2167171150
2267171150
2370161040
2471151040
257215940
267414930
277414930
287613830
297613830
307812820

Wind in September

Winds average 11 km/h in September.

Across September, daily wind ranges from about 11 km/h on the calmest days to 12 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
111calm
211calm
311calm
411calm
511calm
611calm
711calm
811calm
911calm
1011calm
1111calm
1211calm
1311calm
1411calm
1511calm
1611calm
1711calm
1811calm
1912calm
2012calm
2112calm
2212calm
2312calm
2412calm
2512light breeze
2612light breeze
2712light breeze
2812light breeze
2912light breeze
3012light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:54 AM to 6:27 AM, and sunset from 6:55 PM to 6:02 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:546:55
213.05:556:54
312.95:566:52
412.95:576:50
512.85:586:48
612.85:596:46
712.76:016:45
812.76:026:43
912.66:036:41
1012.66:046:39
1112.56:056:37
1212.56:066:35
1312.46:076:34
1412.46:086:32
1512.36:096:30
1612.36:116:28
1712.26:126:26
1812.26:136:24
1912.16:146:22
2012.16:156:20
2112.06:166:19
2212.06:176:17
2311.96:196:15
2411.96:206:13
2511.86:216:11
2611.86:226:09
2711.76:236:07
2811.76:246:06
2911.66:256:04
3011.66:276:02

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.33 kWh/m².

For context, solar energy here swings from a low near 1.32 kWh/m² to a high of 6.57 kWh/m² in June across the year — September's 4.33 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
15.0Bright
24.9Bright
34.9Bright
44.8Bright
54.8Bright
64.7Bright
74.7Bright
84.7Bright
94.6Bright
104.5Bright
114.5Bright
124.5Bright
134.4Bright
144.4Bright
154.3Bright
164.3Bright
174.3Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.0Bright
234.0Moderate
243.9Moderate
253.9Moderate
263.8Moderate
273.8Moderate
283.7Moderate
293.7Moderate
303.6Moderate
Planning a trip in September

Is September a good time to visit London?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

6.6
Sightseeing
2nd-best month of the year
4.2
Beach & pool
4th-best month of the year

September is a reasonable time to visit London for sightseeing.

What to pack for London in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, London sees daytime highs around 21°C and nights near 11°C. Worth packing: rain gear. About 10 days see rain.

rain gear

Sea temperature near London in September

The nearest coast averages about 21°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 41 km away) is warmest in August at about 23°C and coldest in February near 1°C.

It's comfortable for a long swim from Jul 5 to Sep 20 — about 2.6 months when the water holds above 20°C.

0°10°20°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan2Bracing
Feb1Bracing
Mar1Bracing
Apr4Bracing
May10Bracing
Jun17Cool
Jul22Refreshing
Aug23Refreshing
Sep21Refreshing
Oct16Cool
Nov10Bracing
Dec5Bracing

UV index in London in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in London peaks around June 23 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 23UV 9Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr5High
May7High
Jun9Very high
Jul9Very high
Aug7High
Sep6High
Oct3Moderate
Nov2Low
Dec1Low
Location & terrain

Where is London?

London sits at 43.0°N, 81.2°W, 252 m above sea level, in Canada. The nearest listed city is St. Thomas, 24 km away.

Topography around London

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of London.

Within 3 km, the terrain around London has only modest variations in elevation — a maximum elevation change of 62 m around an average of 253 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 118 m; within 80 km, significant variations in elevation — a maximum elevation change of 271 m.

The land around London is covered by artificial surfaces (53%) and trees (36%) within 3 km, cropland (48%) and trees (24%) within 16 km, and cropland (57%) and water (22%) within 80 km.

3 km
62 m
16 km
118 m
80 km
271 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: St. Thomas 24 km · Strathroy 32 km · Woodstock 43 km · Tillsonburg 43 km · Stratford 48 km · Norfolk County 71 km · Brant 74 km · Forest Heights 75 km

Canada travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 83% of US
price level, 2025
GDP per capita
$55,698
2025
Happiness
6.7 / 10
World Happiness, 2025
Safe drinking water
97%
of population, 2024
Homicide rate
2
per 100k, 2023
Road deaths
5.3
per 100k/yr, 2019
Income group
High
World Bank
Religion
Christian 53%none 35%Muslim 5%Hindu 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for London (42.9834°, -81.233°, elevation 252 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).