Will be interested in replies as it is headed our way too. I think every situation will be a bit different and I am sure glad I don't have a mare due to foal or have to worry about mandatory evacuation. Wind, flooding, and power loss will be the big issues here, so in our case the horses with stalls will probably be better off inside our timber frame barn. Any that don't have stalls can still get into the barn and be protected and I will make sure those all have fly masks to protect their eyes from blowing stuff. Planning to fill the big Rubbermaid tub with water, but we also have a brook and I expect there will be plenty of water there for the horses. Our big horse only has a (sturdy) run in, but it has a tarp over the front and I am quite sure the water won't reach him. Fly mask and breakaway halter on him. Will close off pastures to minimize the chance of anyone getting loose and just in case, will close the gate at the end of the driveway. Not looking forward to bailing several inches of water where it ALWAYS floods outside one stall.
Now we have lots of trees so where to park vehicles is a bigger issue! The last major hurricane to hit here was in 1991 when we were on vacation. We returned to a different home to find our back yard FULL of downed trees - but none hit the house.