Sorry to be so negative but are you sure you want to go to Florence in August?
(Sorry, but I have been to Florence and Rome in August.
I was touring by car and Rome was so hot was only stayed half a day and drove back north too cool down).
Found this text on one web site
To talk of the 'weather in Tuscany' is to generalise somewhat. Tuscany encompasses many diverse terrains and landscapes and the rules change from one zone to the next. You can be sure that July and August in Tuscany will be hot, sometimes stiflingly so, thanks to the humidity levels that can make Florence and the major cities of Tuscany veritable hothouses.
And another
The summer months generally have an average of 70 degrees F, with July and August being the two hottest months, averaging a daytime temperature of 95 degrees F. July and August can be particularly a hard time in Florence as the heat can be quite suppressive especially when it is accompanied with the high tourism rates.
Yet another
It is best for visitors to avoid the peak summer months of July and August, when the weather can be unbearably sticky and the prospect of trailing around museums becomes unappealing. Early autumn, when the countryside glows with mellow fruitfulness, is the best time to visit, avoiding the heat and the queues and capitalising on the soft light, empty streets and the abundance of wild mushrooms and just-pressed olive oil.