When temperatures rise in June, some locals depart for cooler weather. Others just turn on the AC and wait for the monsoons to arrive in July.
The word monsoon derives from mausin, Arabic for “season” or “wind shift.” The phenomenon is caused by warm air creating surface low pressure zones that in turn draw moist air from the oceans. Arizona winds usually come from the west but shift to the southeast in the summer, bringing moisture, most often from the Gulfs of Mexico and California. The wind shift and increase in moisture combine with the surface low pressure from the desert heat to produce a cycle of “bursts” (heavy rainfall) and “breaks” (reduced rainfall).
Once the rains begin here, it’s not long before the roadside and hills are covered in bright green, and an afternoon downpour can become almost a daily occurrence. The gentler rains begin without fanfare and their sound is like a soothing whisper. The bursts, however, announce themselves with gusts of wind and thunder and begin with a sudden, powerful downpour that soon begins to flow downhill from higher areas into the dry washes. Riverbeds such as Sonoita and Harshaw Creeks become fast-moving streams, and hilly roads may become impassible as water courses down from above.
This year, the rain began on July 2. It’s an El Niño year, and there have been many predictions about the effect El Niño will have on our summer rainfall. Generally, an El Niño year results in a drier summer in Arizona. However, according to the Climate Prediction Center (CPC), if moisture from an active tropic storm pattern in the East Pacific Ocean occurs at the onset of an El Niño, such as occurred this year, the result can mean an increase in precipitation here.
As of July 29, Patagonia has recorded about 4.7 inches of rainfall according to rainlog.org, and parts of Sonoita are at 5.5 inches.