Good Long Range Forecast site for HOU?

I have been asked about how the weather will be about 18 days or so out for an important gig. Most of the sites I rely on are 10 days out, max. Anyone have a good link to help me out? Thanks!
The following link will take you to the National Center for Environmental Prediction website. The GFS model output for days 1 through 16 can be accessed from this site. The skill level of the GFS out sixteen days is debatable. I look at this model everyday and I can tell you that as of late it has not been doing very good. Over the winter it was usefull only when you could find run to run consistancy. I use it for my construction business, and I have been using it by treating the output like votes in an election; the solution with the most votes was usually "close". Over about the last month and a half it has been highly variable with large discrepencies from run to run. I am not sure whether or not it will perform any better for south Texas than it has been here in Nebraska. In any event I would caution against believing any particular model solution to be gospel that far out.

Thanks. I know that this is a forecast and far out. My friend does too but this is for her outdoor wedding and I am guessing that she is thinking ahead to see if she may need to rent some tents.... 8)