I just say they are unpredictably chaotic. That way they can do whatever I need them to do.
"The fear of death, its risk each time, is one of the most stimulating parts of the game. It therefore behooves the referee to include as many mystifying and dangerous areas as is consistent with a reasonable chance for survival." - J. Eric Holmes
I use tides in my game, but I've never worked out the precise science of them. With two moons, a hexagonal flat earth, Saturn close, and the sun a red giant, I had to throw my scientific calculator out the window.