The rain comes compliments of an area of low pressure that will cross Southeast Mexico this weekend, and then emerges in the Southwest Gulf of Mexico. Right now, models differ quite a bit on where this low is headed. I will say, there are no indicators of an intense wind storm. Heavy rain will likely be the main impact.
Obviously, the track and speed of this low will play a role in rain amounts and location, but it looks like we are likely to see rain Sunday through Wednesday. Over this time, there could be enough rain to cause some degree of flooding in Southeast Texas.