Houston just went into Flash Flood Emergency status for the first time ever according to National Weather Service.
I don't remember Tropical Storm Allison (too young mostly). As far as I know, Allison was worse, but we're catching up pretty fast. Bodies of water are all overflowing one by one. Highway traffic is completely stuck until water goes back down. I haven't heard about any official evacuations, so the metro area is full of millions of people still, including those close to bayous that are overflowing by several feet. Hopefully people will decide not to go to work today if it means crossing roads prone to flooding.
Reportedly, people are still trying to get home from the Rockets game that ended like five hours ago.
Lightning has caused numerous fires and consequently injuries, including a firefighter falling through a burning house.
Radar indicates hail possibly (not confirmed) as large as grapefruits.
6am: Rain has let up and water is finally starting to drain. It will probably still be hours before traffic gets going but at least it's getting better. Importantly, emergency services have been unable to get to people in trouble. Hopefully that improves quickly.
Altogether, some areas saw over 10" (0.25m) of rain.