I've lost power before. In Maryland, I had 2 tanks (75 & 55) that had zero power for 3 days due to a faulty transformer that exploded. (Not weather related.) I didn't do a thing and everything was fine.....
However, if a storm like that hits, power is likely to be out for more than 3 days. In Illinois, an ice storm (sleet and rain that froze on trees and power lines) took out most of my house for a week. Ironically, my bedroom and parts of my basement (where the fish were) had power, but everything else was gone.
Irma, of course, might be much more severe. So, yea, plan for a long haul just in case. Battery power helps, while you can also manually swish water throughout the filters and tank many times each day.