It is officially monsoon season in the Sonoran Desert. Here we know this change brings about RAIN! This precious change in temperature is caused by a shifting of winds. Throughout the year winds in dry subtropical areas tend to blow from land to the sea. Graphic 1: Mean seal level pressure and near surface flow over India, January (dry season)
In the summer, solar heating causes these land masses to warm at a rate that causes air pressure to fall. These thermal lows allow for a shift or a “monson” to shift directions bringing humid air from the cooler oceans to the warmer land masses.Graphic 2: Mean sea level pressure and near surface flow over India, July (monsoon season)
The moist unstable air moves over land masses and when it meets a break in topography (aka the Catalinas in Tucson or the Tibetan plateau featured in the graphics above) the air releases moisture in the form of an awesome and breathtaking storm. The humidity released only triggers more storms. The cycle continues until eventually the ground cools and the winds push on back to the ocean.