Like I said, this seems way worse than "normal" flooding. Not sure if it's due to people used to flooding because most flooding that happened was just due to heavy rain. Hurricanes and tropical storms are still a distinct event, so even if you're used to "normal" floods there should still be the expectation this was something different.
To evacuate a city the size of Houston, and based on the responses of some people there are some people who don't understand that Houston is massive. It can easily take an hour to drive from one side to another without traffic. It would take massive logistical planning. Not sure how you could avoid a Rita like situation unless you forbidded anyone else besides select groups of people on the road at one time. Then you'd need enough people to enforce this. Also you'd have do it as you said way ahead of time which is hard to do with something like this that changes on the hour.
I wouldn't want that job