March to May: The shoulder season in Florence, these months (especially March and April) are cold and wet, with average temperatures around 15°C. Since tourism is slow around this time, you might just get decent discounts on hotels. Interestingly, March is the time Florentines celebrate their New Year.
June to August: These are high season months and bring in major crowds. The prices of hotels tend to shoot and most sights witness long queues. The temperatures hover between 20°C to 30°C and the weather is pretty warm. The exciting Florence Dance Festival takes place in June and July.
September to November: September and October are pleasant months in Florence and account for the shoulder season, yet again. September can get a tad bit crowded owing to the Festival of Paper Lanterns and the Nativity of Virgin Mary. November starts to get cold and wet with temperatures falling below 15°C.
December to February: These are the coldest months in Florence as temperatures fall to single digits. While it happens to be the low season, Christmas and New Year celebrations usher in a lot of tourists, and hotels tend to book up.