Fox News reported that Highway 90 was not an option as it's bridge is damaged. Know another way?
How fast can the Army Corps of Engineers put together a bridge?
US 80 and 84 appear to have sections closed as well, as well as many local roads. You probably can bypass the problem on 84 by staying on I-85 to Opelika, take 280 to Columbus, and then hit Z. Cross -country traffic should probably try I-20.
Note I-10 is blocked in Alabama as well, along with 90 and 98.
Here's a list of Alabama road closures and reasons:
http://www.dot.state.al.us/closures/
Mississippi hurricane road closures:
http://www.mdot.state.ms.us/
Florida doesn't seem to care about posting information where it can be found. FlDOT links to the state disaster page, which links back to FlDot traffic count info.