Here is the National Hurricane's Center forecast for what is now tropical depression Harvey. I have
The map shows the system, weakened to tropical storm strength, hovering around the Texas coast. This slow movement is a recipe for severe to catastrophic flooding. The European model (below)
As to preparations: Be prepared to evacuate, because of rising waters, on short notice. You may wish to load the car in advance with essentials. This includes any family heirlooms.
I would obtain extra cash (ATM's and cash registers do not work during power failures) and fill my car with fuel. Fresh batteries are essential along with a flashlight. If you live in a flood-prone area, make a reservation at a hotel and know your escape route.