Very simply put, Katrina is going to cause haoc with all the carriers schedules all over the US. It's going to happen, nothing to do about it but pray for those in her path.
Keep an eye on your carriers web site. At this point it's a crapshoot what will happen. Your flight could be on time, late, or cancelled altogether. It's quite possible that if you can fly out a day early your carrier will accomodate you at no additional charge to change plans.
Anne