Arizona Monsoon Season 2021 Weather Hazards and Safety Risks to Watch Out For

Arizona's monsoon season runs from June to September, officially from June 15 to September 30, according to the National Weather Service.

However, in northern Arizona, "monsoonal moisture typically does not reach the region until the first week of July," the NWS says.

"Many different factors throughout the spring and early summer influence when exactly it begins each year. Much of the area receives 40 to 50 percent of it's annual precipitation during monsoon season," it adds.

Due to the higher humidity level, the season can cause thunderstorms, heavy rain, lightning, hail, high winds, flash flooding, dust storms and extreme heat, the Arizona Department of Transportation (ADOT) says.

The U.S. National Oceanic and Atmospheric Administration (NOAA) warns Arizona and its residents can be impacted by "life-threatening and damaging weather hazards" during monsoon season.

What is a monsoon?

The NWS explains a monsoon refers to "large-scale wind shifts that transport moist tropical air to dry desert locations, such as the southwestern United States."

A monsoon pattern impacts several other regions across the globe, including Southeast Asia, Australia, Africa and South America. "The Indian Monsoon is the strongest in the world due to the height of the Tibetan Plateau," the NWS says.

What causes a monsoon?

These wind shifts are caused by the "intense heating" of the land over Mexico and the southwestern portion of the U.S. during the early summer months, which causes wind shifts in the low levels of the atmosphere, NWS says.

Moisture is carried off of the Gulf of California and eastern Pacific Ocean, which form the two main sources for "monsoonal moisture" in northern Arizona. The winds transport moisture towards the north into Mexico and the American Southwest.

Another key aspect of monsoon development is in the atmosphere's upper levels. A "strong subtropical ridge of high pressure" over Mexico in June blocks moisture flow toward the north, the NWS explains.

"This is why northern Arizona normally sees some of the hottest and driest weather of the year during June. However, as we head into late June and early July the ridge of high pressure shifts northward into the Southern Plains or Southern Rockies.

"The shifting ridge axis allows low and mid level moisture to move northward. The combination of the low, mid, and upper level moisture surge to the north culminates in the real beginning of the annual monsoon season," the NWS adds.

Weather hazards and safety risks

The NOAA says: "The early part of the monsoon season (June), is typically drier and very hot. During this part of the season, fire danger is extremely high. This is because there are more high-based dry thunderstorms that cause dry lightning and gusty winds."

The Arizona Department of Health Services (ADHS) warns: "Flooding is a real danger during the monsoon season. Arizona's dry and rocky soil does not absorb water well, so flood conditions can develop very quickly and without warning after a heavy rain.

"Without proper safety measures, these extreme weather conditions can result in multi-vehicle accidents on Arizona roadways," the ADHS adds.

The ADOT also warns drivers to "be cautious of hydroplaning" during monsoon season.

"This occurs when a thin layer of water accumulates between your tires and the asphalt and your vehicle loses contact with the roadway. You might suddenly feel your vehicle sliding or drifting because you've lost traction," it adds.

See the ADOT website for more information on driving safely during monsoon season in Arizona.

Residents could also suffer from heat stroke during monsoon season, the symptoms of which can include the following, as outlined by the NOAA.

  • High body temperature
  • Altered mental state or behavior
  • Alteration in sweating
  • Nausea and vomiting
  • Flushed skin
  • Rapid breathing
  • Racing heart rate
  • Headache
A river flooding in Arizona in 2004.
Residents watching the Agua Fria River rush by in downtown Black Canyon City, Arizona due to heavy rainfall in December 2004. Arizona's monsoon season, which runs from June to September every year, can bring heavy rain, flash flooding and other extreme weather conditions. Jeff Topping/Getty Images