Rome enjoys of a Mediterranean climate typically soft, generally in all the Italian coast. In the Winter, temperatures go down being the coldest months January and February, and it gets cold just at night, during the day it is very mild. These winter months can also be with rain. The hottest months are from June to September, but August is always a very hot one, with a lot of humidity as well.
When to go
It is amazing to visit Rome at any moment of the year, but it always depends on your taste. If you don’t like the hot weather and the crowded streets, then don’t go in the Summer, go better in the Autumn or Spring, probably the best months are April and May. If you are going in the Summer be prepared for the very hot days and also nights.