I live in west louisiana and just like all of our gulf coast and eastern seaboard hobbiest friends, this is a problem that we all deal with. The answer to your question is going to be rather vague as a lot of variables will enter into the equation. If it is really hot, things will not last long at all.
If it is in the low 80's or so, I would think you would safely have 24 hours. All of my tanks and inhabitants survived Rita, but only because of the generator.
Although I cannot prove it helps, I do a large water change in all my tanks when a hurricane is in the neighborhood. In my thoughts, I am giving things a better chance by doing what I can to avoid high ammonia/nitrite issues. I also keep bottles of water in the freezer to toss in the tanks.