Phoenix experienced its hottest summer on record, breaking the marks achieved in 2016 and 2019. The average temperature from June through August was 96 degrees, which surpassed the previous record held in 2016 of 95.4 degrees, according to the National Oceanic and Atmospheric Administration.
And Phoenix is not alone. The entire Northern Hemisphere experienced its warmest summer yet, and globally, the planet observed its second hottest summer on record.
There are several theories as to why the U.S. suffered through such high temperatures, but Peter Crank, a Ph.D. candidate at Arizona State University’s School of Geographical Sciences and Urban Planning, said it’s in part due to the very strong, high pressure experienced throughout much of the Western portion of the U.S., including Arizona.
“High pressure typically indicates sunny skies and warmer weather,” Crank said. “This high pressure stuck around a lot longer than it normally does and it stayed very strong.”
This high pressure restricted moisture, which normally comes up from Mexico into Arizona, and triggers the seasonal monsoon precipitation. This resulted in Arizona having a much drier monsoon season than normal, leading to hotter temperatures as well. This same high pressure was also responsible for the warmer temperatures in California, Nevada, Utah and other states across the West.
Also, because this high pressure was so far west this year, it enabled Atlantic hurricanes to move deeper into the Gulf of Mexico with greater intensity and associated precipitation.
Crank explained that during most summers in Phoenix, the air temperatures are typically at their highest points in June, but this summer saw those temperatures continue throughout July and August.
He also said that Phoenix has not only broken its record for the hottest average temperature this summer, but also its record for the number of days exceeding 110 degrees.
“We have (had) 53 days this year so far and the previous record was 33, so we nearly doubled the number of days we spent above 110 degrees this summer,” he said.
Phoenix is also close to breaking its record for the number of days above 100 degrees in a single year. Currently, the city has experienced its second highest yearly total on record with 139 days above 100 degrees. The standing record number of days for an entire year is 143 days which occurred in 1989.
Downtown Phoenix has also experienced a greater increase in temperatures as urbanization grips the city, according to Nancy Selover, a research professor at ASU’s School of Geographical Sciences and Urban Planning.
Downtown Phoenix is growing at a rapid rate resulting in mass construction. This construction often leads to an increase in temperatures as it can affect local wind and water cycle patterns, according to the American Geophysical Union.
Selover said that because of this substantial urban development, the nighttime temperatures in downtown Phoenix were much higher than usual and continue into the morning hours.
“That meant the day already started warmer than normal, so it just got hotter from there,” Selover said. “This helped the heat waves persist for more consecutive days.”
Selover said she doesn’t think Phoenix’s warmer temperatures will go away any time soon.
“We are seeing October continue to be much warmer than normal, and even though next week should drop below 100 here, it will still be warmer than normal,” Selover said. “That is likely to continue through the end of the year.”
Contact the reporter at amstansf@asu.edu.
