The pictures of Houston are just insane.
The local government is also going to have to do a lot of explaining. They told people not to evacuate and predicted half the rain totals they've gotten. Maybe it was another wrong prediction as is the case with weather often, but it seems like they were tragically off the mark with this one and went out of their way to discredit some people predicting much higher rain totals.
Example: a lot of posts from people on Facebook who claimed to know people with inside info and predicting 50+ inches of rain and catastrophic flooding were outed as fake by local government and media, yet all those Facebook postings are becoming a reality.
A full scale evacuation probably would have been a disaster, and stranded people on those highways that were flooded with 12+ feet of water, but you have to wonder about being able to evacuate a city in this day and age when you have a storm this big barrelling toward you, intent to do damage.
He's already explained it: You can't put 6.5 million people on the road. You just can't. If you try, half of them will stay put anyway, and the other half will get washed off the road while they're stuck in the mega-traffic jam. (Which they already know about from what happened with Rita.) So, then you have 2 mega-crises instead of just 1.
As for the estimates, the NOAA people flat-out said that what is happening is beyond anything they know how to think about. This wasn't about bad calls. It's about a huge storm being way more stuck in one place than any huge storm anybody has ever seen.
It's made worse by they fact that much of the natural drainage features of the land has been paved over with disregard for flood plains and other relevant things. Good planning has been anathema to the pro-developer attitude of the area.