Our roads do that, too, but it seems to be independent of rain, weather or anything else. Probably the same reason my house's foundation does it: The whole state of Louisiana is either red clay or swamp. The clay is so elastic that with the slightest changes in moisture, it expands/contracts. I've been told (and tend to believe) that Louisiana homeowners 1) will have foundation problems, 2) are fixing foundation problems or 3) have already fixed foundation problems. I suspect the same is true of Louisiana roads. On the other end of the spectrum, I've seen roads in west Texas (rock / mountains) that are 20 years old and look virtually brand new. Unfortunately for cyclists, those roads are often chip seal and could benefit from an upgrade.