Now the models predict it goes up the east coast of Florida. Even if it does that, Key West may not survive. Pack up anything you want to keep and head north, before it's too late. The bridges out the Keys probably won't all survive, and if just one gives out you're stuck there. If you are in a car on the Keys when Irma goes by, you WILL drown.
I'm not even sure where you can go: All of Southern Florida is pretty damned flat and pretty damned low. People will have plenty of opportunity to drown if they are stuck in traffic jams while evacuating in Southern Florida. Even when you get further North, the land is flat you could be flooded out from the rain.