What is a Monsoon? The amount of rain in Maricopa County is highly variable from year to year, but one thing that County residents can rely on is the monsoon. A monsoon refers to a change in the seasonal wind direction. The term is correctly used to describe a season, much in the same manner as using the term "summer. The terms "monsoon" and "thunderstorm" refer to different weather events, but it is correct to say "monsoon thunderstorm