Click on a day for an hourly weather forecast
The temperatures in Siena in September are comfortable with low of 14°C and and high up to 26°C.
You can expect about 3 to 8 days of rain in Siena 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 Siena in September 2025.
If you’re planning to visit Siena in the near future, we highly recommend that you review the 14 day weather forecast for Siena before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | 9° / 2° | 5 | 25 | 1 | 74 mm | Ok | Siena in January |
| February | 10° / 2° | 5 | 21 | 2 | 85 mm | Bad | Siena in February |
| March | 14° / 4° | 5 | 25 | 1 | 73 mm | Good | Siena in March |
| April | 18° / 7° | 5 | 25 | 0 | 64 mm | Good | Siena in April |
| May | 21° / 9° | 6 | 25 | 0 | 91 mm | Good | Siena in May |
| June | 27° / 14° | 6 | 24 | 0 | 70 mm | Perfect | Siena in June |
| July | 30° / 16° | 3 | 28 | 0 | 42 mm | Good | Siena in July |
| August | 31° / 17° | 3 | 28 | 0 | 38 mm | Good | Siena in August |
| September | 26° / 14° | 4 | 26 | 0 | 81 mm | Perfect | Siena in September |
| October | 20° / 10° | 4 | 27 | 0 | 79 mm | Good | Siena in October |
| November | 14° / 7° | 6 | 24 | 0 | 105 mm | Good | Siena in November |
| December | 10° / 3° | 5 | 25 | 1 | 74 mm | Ok | Siena in December |