Climate averages 1991–2020
Cardiff weather
in September.
A mild, moderately wet month: the 4th warmest and the joint 5th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a mild month in Cardiff: daytime highs average 17.2°C and nights cool to about 11.5°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 74 mm of rain on roughly 11 days, which makes September a moderately wet month (the joint 5th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 42 min on an average September day.
The nearest other city in this atlas is Newport (17 km away). In September its highs average 17.8°C, 0.6°C warmer than Cardiff, with 63 mm of rain.
Among the 143 cities listed in the United Kingdom, Cardiff ranks joint 83rd of 143 for the warmest September highs and 122nd of 143 for the driest September (rainfall, lowest first). The mean September high of those 143 cities is 17.3°C; Cardiff is 0.1°C cooler than that mean.
From September to October, average highs fall by 3.5°C to 13.8°C, and monthly rainfall rises from 74 mm to 106 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Cardiff climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 7.4°C3.3°C | 3.3°C | 95 | 14.5 | 8.48 h |
| February | 7.8°C3.0°C | 3.0°C | 75 | 11.3 | 9.910 h |
| March | 9.6°C3.9°C | 3.9°C | 68 | 11.7 | 11.812 h |
| April | 12.2°C5.5°C | 5.5°C | 70 | 11.6 | 13.814 h |
| May | 15.2°C8.5°C | 8.5°C | 73 | 12.3 | 15.616 h |
| June | 17.7°C11.4°C | 11.4°C | 71 | 11.0 | 16.517 h |
| July | 19.4°C13.4°C | 13.4°C | 74 | 11.6 | 16.116 h |
| August | 19.2°C13.5°C | 13.5°C | 87 | 12.3 | 14.615 h |
| September, selected | 17.2°C11.5°C | 11.5°C | 74 | 11.0 | 12.713 h |
| October | 13.8°C9.0°C | 9.0°C | 106 | 14.0 | 10.711 h |
| November | 10.3°C6.1°C | 6.1°C | 102 | 14.5 | 8.99 h |
| December | 7.9°C3.9°C | 3.9°C | 107 | 13.7 | 7.98 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Newport in SeptemberUnited Kingdom · 17 kmHigh 17.8°C · Low 10.9°C · 63 mm rain
- Weston-super-Mare in SeptemberUnited Kingdom · 21 kmHigh 17.8°C · Low 11.6°C · 60 mm rain
- Bristol in SeptemberUnited Kingdom · 41 kmHigh 17.8°C · Low 11.0°C · 56 mm rain
- Swansea in SeptemberUnited Kingdom · 55 kmHigh 16.8°C · Low 12.1°C · 96 mm rain
- Bath in SeptemberUnited Kingdom · 58 kmHigh 17.5°C · Low 10.6°C · 56 mm rain
- Gloucester, United Kingdom in SeptemberUnited Kingdom · 78 kmHigh 18.0°C · Low 10.8°C · 54 mm rain
- Exeter in SeptemberUnited Kingdom · 88 kmHigh 17.5°C · Low 11.5°C · 53 mm rain
- Cheltenham in SeptemberUnited Kingdom · 89 kmHigh 17.9°C · Low 10.7°C · 57 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Cardiff) is explained once on the Cardiff year overview and on the Sources, method and limits page.