A wife here. Yeah, tell her the dates and that it's a beach so she can be sure to get all the pre-beach things done. You can still surprise her with the location, but she will be prepared also. You know we have to starve for a couple of weeks and tan ourselves first so we'll feel a tiny bit better about ourselves in a bathing suit.
As far as the Caribbean in Sept, I lived on St Thomas, USVI, the last 2 Septembers and there were always tropical waves coming through. Try Grenada or Curacao Sandals. They seem to be a little further out of the hurricane zone although they still can get hit.
Aruba is like Destin, but on an island.
If you do decide to go in Sept and want an AI, Sandals Emerald Bay in Exuma, Bahamas, is gorgeous. Hubby got to play golf on the course that overlooks the water. I drove the cart and took pics. Rent a car there and go to Cocoplum beach when the tide is out. Just stunning. Trust me.