Weather in Cardiff in September 2025
Average weather
Average temperature in Cardiff in September
Going from a maximum of +28°C during the day to a minimum of +6°C during the night, the temperature in September averages around +21°C.
The average maximum temperature goes down 14% by the end of the month, compared with the beginning of the month, from +21°C to +18°C.
Is Cardiff warm or cold in September?
Cardiff is typically mild in September.
Maximum temperatures go down compared to the previous month from +20°C to +18°C. The minimum temperature also goes down from +14°C to +12°C.
Pack a light jacket as it will be warm in the day and cool in the evenings.
Take a look at how September is compared to other months in Cardiff:
Water temperature in Cardiff in September
Water in Cardiff in September is Fresh. It varies from +16°C to +17°C, with an average of +17°C. This is almost similar to the air temperature, which averages +18°C.
The water temperature in September is one of the warmest of the entire year:
Can you swim in Cardiff in September?
Climate in Cardiff in September
| August | September | October | ||||
|---|---|---|---|---|---|---|
| Avg. temperature | ||||||
| +20°C | +18°C | +15°C | ||||
| Min. temperature | ||||||
| +7°C | +4°C | -3°C | ||||
| Max. temperature | ||||||
| +33°C | +29°C | +26°C | ||||
| Rainfall | ||||||
| 85 mm | 84 mm | 119 mm | ||||
| Wind | ||||||
| 4 m/s | 4 m/s | 4 m/s | ||||
| Avg. water temperature | ||||||
| +17°C | +17°C | +15°C | ||||
| Humidity | ||||||
| 78% | 79% | 82% | ||||
| Air pressure | ||||||
| 1014 HPa | 1015 HPa | 1012 HPa | ||||
| Sunny days | ||||||
| 3 | 3 | 2 | ||||
| Cloudy days | ||||||
| 10 | 10 | 8 | ||||
| Rainy days | ||||||
| 17 | 17 | 20 | ||||
| Snowy days | ||||||
| 0 | 0 | 0 | ||||
September weather is still as ok as in August. It’s getting colder in September. From +20°C in the day, the average maximum temperature lowers to +18°C. As September arrives, the amount of rainfall goes down. On average, the rainfall volume decreases from 85 mm to 84 mm. Humidity rises from 78% to 79%. The average wind speed doesn’t change much during September, staying around 4 m/s. The amount of sunny days stay about the same, averaging 3 sunny days during the month.
October brings much the same weather, it remains ok.
Wind
The average wind speed is 4 m/s getting up to 8 m/s which is a medium breeze. You can feel it, especially getting out of the water.
The average wind speed in Cardiff is gradually increasing during September, going from 2 m/s to 3 m/s over the course of the month.
Rain
How was the weather last September in Cardiff?
Climate Change over Years
The climate in Cardiff in September has not changed much over the last 43 years.
The average temperature was the lowest in 1979 (+12°C) and the highest in 2022 (+16°C). The driest year was 2010 with only 736 mm of rainfall, and the wettest year was 2022 with 1906 mm.
FAQ
Is September a good time to visit Cardiff?
Can you sunbathe in Cardiff in September?
Can you swim in Cardiff in September?
Is Cardiff rainy in September?
Is it sunny in Cardiff in September?
Other cities in United Kingdom
Monthly weather in Cardiff
Source of the data
For this page, we’ve looked at the typical weather in Cardiff, based on historical hourly weather data from January 1, 1979, to December 31, 2023.
For past dates, we show actual recorded data at the location at that time. Forecasts are based on recorded weather during that day of the year, averaged over the total years for which we have records (unless stated otherwise). The daily temperature is the highest recorded temperature in the shadow during that day.