Weather Underground put it in boldface (scroll down a bit), so I think it is worth a pull-quote:
There is very little doubt that Texas is in for one of the worst rainfall and flood events in its history. The resulting rainfall is very likely to produce widespread, devastating, and potentially catastrophic flooding.
Most dire is the outlook for Houston, “given that city’s vast size and population and its well-known vulnerability to flooding.”
Good luck to all there and throughout Coastal Texas, and pardon the near-cliche, but don’t drive into water – most flood victims, I hear, are found in their vehicles.
To follow developments real-time, WU recommends: