The University of Arizona is predicting our summer monsoon rains “to be more vigorous than average, with a strong beginning and end.” See full story here. The Old Farmer’s Almanac is predicting “near normal rainfall.” See here.
Arizona’s monsoon in July, August, and September occurs because a high-pressure area perches over the Four-Corners area and draws moist air from the Gulf of Mexico and the Gulf of California. The mountains and summer heat cause updrafts that condense the moisture-laden air to produce rain from thunderstorms.
To better understand thunderstorms, see my post Anatomy of a Thunderstorm.