Cardiff weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Good
Best time to visit: June – September
What is the weather like in Cardiff in September?
In September, Cardiff is mild: daytime highs average 18 °C, and nights cool down to about 12 °C. The sea averages 17.2 °C – bracing, so a wetsuit helps for longer swims. Expect around 5 hours of sunshine a day. Rain is frequent, with about 10 rainy days and 63 mm in total. All in all, September is a good month for a holiday in Cardiff.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 74 | 71 | 41 |
| Day | 19° | 18° | 14° |
| Night | 14° | 12° | 10° |
| Sea | 18° | 17° | 15° |
| Sun | 6 h | 5 h | 4 h |
| Rain days | 12 | 10 | 14 |
More details for September
- Daylight
- 12 h 44 min06:46 – 19:30
- UV index
- 4 · moderateclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or moreAll months
- Wind
- 22 km/haverage daily peakAll months
- Cloud cover
- 68 %on averageAll months
- Hot days
- 0 days30 °C or more
- Time zone
- UTC+1Europe/London
How the score comes together
- Temperatureweight 50 %95 %
- Sunshineweight 20 %33 %
- Few rainy daysweight 30 %56 %
Each factor is rated from 0 to 100 % and weighted for the travel style “City break”.
What to pack in September
- Sunscreen
- A jumper for the evenings
- Rain jacket or umbrella
Cardiff in September: quick answers
Is Cardiff hot in September?
No. In September, Cardiff is mild: daytime highs average 18 °C and nights drop to about 12 °C.
Can you swim in Cardiff in September?
Only if you don't mind cold water: in September the sea averages just 17.2 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in Cardiff in September?
Rain is frequent, with about 10 rainy days and 63 mm in total.
Cardiff month by month
The whole year in CardiffAll destinations: United KingdomWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences