Lightweight summer coat that has lots of vents

Florida heat. Florida sun. Florida rain. It's awesome but definitely an impractical place for most clothing. I want a coat that hangs long (below butt) and has lots of underside venting- under armpits, flap on back of shoulders, loose sleeves at wrist that can be buttoned to the middle of arm. The challenge is that it needs to be lightweight enough to allow the flapping of the fabric to funnel air around your body to keep you cool, but still keep the afternoon rainshowers from drenching you. Or maybe have it just let you get wet and then dries in a flash. This is bigger than just a shirt that does these things so that you can wear it constantly to block the heat and improve airflow.