Click on a day for an hourly weather forecast
The temperatures in Cornwall in September are comfortable with low of 11°C and and high up to 21°C.
You can expect about 3 to 8 days of rain in Cornwall during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Cornwall in September 2025.
If you’re planning to visit Cornwall in the near future, we highly recommend that you review the 14 day weather forecast for Cornwall before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -4° / -12° | 11 | 15 | 5 | 27 mm | Awful | Cornwall in January |
| February | -3° / -12° | 10 | 13 | 6 | 29 mm | Awful | Cornwall in February |
| March | 3° / -6° | 9 | 18 | 5 | 30 mm | Awful | Cornwall in March |
| April | 11° / 1° | 8 | 20 | 1 | 41 mm | Ok | Cornwall in April |
| May | 19° / 8° | 8 | 23 | 0 | 39 mm | Good | Cornwall in May |
| June | 22° / 12° | 8 | 22 | 0 | 44 mm | Good | Cornwall in June |
| July | 26° / 16° | 8 | 23 | 0 | 39 mm | Perfect | Cornwall in July |
| August | 25° / 15° | 8 | 23 | 0 | 41 mm | Perfect | Cornwall in August |
| September | 21° / 11° | 7 | 23 | 0 | 37 mm | Good | Cornwall in September |
| October | 14° / 6° | 8 | 23 | 0 | 45 mm | Good | Cornwall in October |
| November | 6° / -1° | 8 | 20 | 2 | 29 mm | Awful | Cornwall in November |
| December | 0° / -6° | 12 | 14 | 5 | 35 mm | Awful | Cornwall in December |