The summer of 2024 ended Saturday as the hottest on record in Phoenix, melting the old mark by 2 degrees just a year after it was set.
At the end of the meteorological summer, the average temperature in Phoenix over June, July and August was 99 degrees, compared to 97 degrees in 2023, which until this year was the hottest summer on record.
“We’re currently 2 degrees ahead of last year, which was the hottest meteorological summer,” said Matt Salerno, meteorologist for National Weather Service Phoenix.
Phoenix warmed up early in June, compared to a relatively cool month last year, which Salerno believes contributed to this year’s record.
“It didn’t really heat up until July last summer,” he said. “Whereas this summer it has been persistently hot since basically June 1. We’ve been above normal pretty much every single day.”
The summer rewrote weather history along the way, setting nine new record high temperatures and 19 new records for high minimum temperatures. The high temperature hasn't dropped below 100 degrees since May 26.
A high-pressure atmospheric system that traps heat below has impacted most of the Southwest throughout the summer, particularly in June and July in Phoenix.
While last summer will likely maintain its record as the driest summer, lower-than-normal rainfall totals this summer helped maintain high temperatures. Phoenix Sky Harbor International Airport has recorded 0.75 of an inch of rain this season.
Climatologists and meteorologists use four meteorological seasons divided into three months each to track weather trends and records, rather than astronomical seasons based on Earth’s rotation around the sun.
The frequency of new records concerns climatologists, who see the trend as further evidence of the role climate change plays in more climate extremes and above-average temperatures.
“The things that were rare are becoming less rare,” said Michael Crimmins, climatologist for the University of Arizona. “Everybody knows it's hot here in the summer, and you think 'Well, it can't be that hot again next summer,' and then it is.”
"And even if you don't break a record every summer, but you're so many degrees above average, that's just an indication of a shift in the climate," he added.
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Record heat almost everywhere
Phoenix may have a reputation as one of the hottest cities, but the rest of the country was not immune to the heat.
Salerno said other areas in Arizona and across the West are breaking heat records, too. Yuma is on track to have its hottest summer ever and Flagstaff will likely have a top-three record as well.
Palm Springs (124 degrees on July 6) and Las Vegas (120 degrees on July 7) posted all-time record high temperatures this summer, and Death Valley neared 130 degrees.
"Nobody is coming in at the average," Crimmins said. "Everybody's really pushing the envelope as far as the rankings."
This summer was also the most humid in the U.S. in the last 85 years of record-keeping. While cities like Washington, D.C., or New York City don’t often have triple-digit temperatures, a high dew point can make summer days feel hotter and more dangerous as the human body struggles to cool off.
July also produced two of the hottest days on Earth ever recorded when the average global temperatures on July 21 and 22 surpassed the highest previously recorded.
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The outlook? A hot start to fall
While meteorological fall starts Sept. 1, Phoenix residents likely won’t see any relief from the heat anytime soon.
“We’re going to be seeing highs at least 3 to 5 degrees above normal this weekend,” Salerno said. “Heading into the middle of next week the ridge of high pressure will probably rebuild right on top of us and provide a lot of heating for us again.”
“We’ll probably see highs above 110 as early as Wednesday. We’re looking at some pretty extreme temperatures for this time of year,” he added.
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Climate Central predicts above-normal temperatures will continue across the U.S. from September through November. The Southwest has seen increasingly warmer autumns, with a 3.8-degree average increase from 1970 to 2023.
Tucson and Phoenix were in the top five fall warming locations, with an average increase of 5.6 degrees and 5.4 degrees, respectively.
More records forecast
While this meteorological summer is ending as the hottest ever, this likely won’t be the only heat record Phoenix breaks this year.
Aug. 29 was the 95th consecutive day with a high temperature over 100 degrees, breaking the previous record of 76 days in 1993. There have also been 37 days when Phoenix posted 90-degree-plus lows in the mornings, beating 2023’s record of 34 days.
To date, there have been 102 days in 2024 over 100 degrees, still shy of the last record of 145 days in 2020.
“We’d still need a solid month and a half plus of 100-degree temperatures to get to that mark,” Salerno said.
Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic andazcentral.com. Email her with story tips athayleigh.evans@arizonarepublic.com.
