No one wants to tell someone not to leave, and then have it all go bad, but 90% of the time, you're going to actually be safer to stay put in a well built and secured home that's surrounded by wind-tolerant vegetation (palms, properly-trimmed live oaks, longleaf pines=goof; shortleaf pines, laurel oaks=bad) and not in a flood zone.
Unnecessary evacuation makes it hard for people who live in truly at risk areas to leave those areas, and being on the road with so many other people is dangerous. I know people who live on the west side of Houston at a good elevation who evacuated for Rita, and that's far, far inland to begin with. All they ended up doing was clogging the roads even more. Not to mention a huge number of traffic deaths from a storm that eventually hooked north and didn't come anywhere close to Houston.