Generally, average temperature in Siena right through the month of September is 18 with the high being 23 degrees celsius and a low of 15.
| Month | Degrees Celsius |
|---|---|
| Temperature | 18 |
| High Temperature | 23 |
| Low Temperature | 15 |
| Sunshine Per Day | 8 |
Useful Links: Siena Weather: Average Weather & Yearly Climate