- Arizona's monsoon season begins in June and continues through September - With it comes higher humidity, which can lead to thunderstorms, heavy rain, lightning, hail, high winds, flash flooding, dust storms, and extreme heat - Stay out of flooded washes!! Seriously ... that water has far more power than you could imagine. - Seems we have at least one fatality each year from someone driving into a running river that they were used to seeing dry most of the time