September is definitely the rainier month,I live in Florida so I know.May is actually more similar to October as they're both transitional months.The end of dry season ends in May,it could be early or late May as some years a good chunk of May is still pretty dry.October is also what I would consider transitional as the daily rain and somewhat cooler weather usually comes in between the middle and end of the month,the early part is still usually rainy.September is pretty much always a humid,rainy mess.As somebody else mentioned even that's not guaranteed you could get some nice days as well but generally speaking September is humid and rainy.I mean we're in the nicer months of the year right now and from Christmas through the first two weeks we had a lot of overcast and rainy days even though it's usually nice and sunny,so no guarantees ever in Florida.