I am not sure how many hurricanes you have experienced in Montana by living all of my life in Texas and Lousiana I have been through quite a few with very infamous names.
Now, for your time line. Katrina made landfall on the morning of Monday, August 29th not August 27th as you stipulate.
Seventy-two hours advance notice would have been nice for the people of New Orleans but 72 hours prior to Katrina hitting the MGC and New Orleans the storm was a CAT 1 just entering the Gulf of Mexico.
Perhaps you should check your facts before posting.
Doesn't matter. When there's a hurricane barrelling down on you, you get the hell out.