Don't count on land features to keep tornadoes away. Historical evidence that they work is not, repeat not backed up by scientific evidence.
People in NE Texas really need to start thinking about catastrophic flooding; the one saving grace of Katrina is that it moved quickly once inland and never interacted with other features to cause much of anything in terms of inland flooding.
However based on the way the models are going you're potentially looking at catastrophic, 500-year-type flooding in the NE part of Texas as the storm gets stuck. Think North Carolina in Floyd.