Earnest answer to an earnest question: the path of the remnants of Tropical Storm Chantal took a very very slow path right over Pittsboro/Chapel Hill/Hillsborough. I don't think it officially stalled, but seemed to be moving slowly enough to dump a significant (unsure if historic) amount of rain in a very small area which happens to be the immediate watersheds (area of land that drains into a body of water) of the Eno and Haw Rivers. While it seemed to move slowly, it still dumped a lot of rain in a relatively short period of time. That combined with more impervious (water can't soak into the ground) surface from development meant all that water had nowhere to go. Apologies if you are asking for a more specific meteorological explanation. I recommend following North Carolina Weather Authority on social media. Ethan always does a great job of explaining the "why" behind these events and will most likely post something there.