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As this year’s monsoon ends, Phoenix residents will likely remember the season for its heat rather than rain.
Arizona saw scattered thunderstorm activity, with lackluster haboobs descending on the Valley, a handful of small storms and even a rainbow over downtown Phoenix. But it was the hot weather that stood out, all the way to the season's end this week when a heat wave sent temperatures soaring back over 110 degrees.
And while it wasn’t as dry as last year — the driest monsoon on record — this year’s monsoon will land in the top 10. The monsoon season officially ends on Sept. 30, but with no rain in the forecast through the weekend, current rainfall totals appear final.
As of Sept. 25, the National Weather Service recorded 0.74 of an inch of rain at Phoenix Sky Harbor International Airport, less than a third of normal, making this the seventh-driest monsoon since records began in 1896.
“This was the hottest summer on record for the state, and the precipitation was hit or miss,” said Erinanne Saffell, Arizona’s state climatologist. “We didn’t see anything in Maricopa County that we wanted to see. It was really dry in the central and western part of the state.”
While Phoenix won’t be breaking any records for the monsoon on either end of the spectrum, America’s hottest city broke a stack of heat records over the last few months.
Here’s what to know about this year’s monsoon and how it played a role in Phoenix’s hottest summer on record:
Summer weather: Why is the monsoon so unpredictable? It takes a lot to make a good thunderstorm
How much rain did Arizona get?
Following last year’s record hot and dry summer, Saffell — along with the rest of heat-weary Phoenix — hoped for a productive monsoon that would offset high temperatures. June precipitation triggered a false alarm.
“This summer started out really hot, but we actually got wet at the end of June. It gave us hope,” Saffell said. “But then we started getting very hot and staying very hot, and not as much precipitation in July.”
The monsoon was below average in Phoenix, the 0.74 of an inch at the airport well below the 2.28 average.
The Maricopa Flood Control District also maintains over 300 rain gauges across the county, which provide an overall picture of monsoon activity for the region as the district calculates the average from all of its gauges.
The 40-year average for monsoon rainfall in Maricopa County is 2.97 inches. But in 2024, the average for the season in the county was 1.43 inches, which is 46% of normal, according to Daniel Henz, the flood warning branch manager for the district.
“We definitely weren’t as bad as 2023 or 2020, but we’re definitely very dry,” Henz said. “This is the third-driest monsoon on record when averaged around the county.”
Monsoon 2020 was the driest and 2023 was the second-driest, according to the district's rain gauges.
“There were some places that actually did OK, but overall it looks like the state is going to end up on the dry side,” Saffell said.
Tucson recorded above-average precipitation, with 5.8 inches of rain, compared with its average of 5.69. Flagstaff averages 7.68 inches and recorded 6.08 this season.
Pima, Cochise, Globe, Coconino and Pinal counties also did well, according to Saffell.
Along with Phoenix and south-central Arizona, the northwest and southwest portions of the state, particularly Yuma, were drier than normal.
How did the monsoon contribute to the hottest summer on record?
While this may not have been the driest summer on record, it was the hottest. A sporadic monsoon contributed to record-breaking heat across Phoenix and the state.
Phoenix broke several heat records this summer: most days over 110 degrees, most consecutive days over 100 degrees and the hottest meteorological summer on record, with an average temperature of 99 degrees.
The state also experienced its hottest summer on record, with an average temperature of 82.1 degrees.
Heat is one of the main ingredients needed to trigger monsoon storms. A high-pressure system begins moving north into the Southwest in May, bringing moisture into the region from Mexico.
“At the start of the monsoon season, what we really want is getting it really hot in the Four Corners region,” Saffell said. “That allows moisture to come from the south, it kind of draws into Arizona and it starts giving us that moisture that we can drop out as thunderstorms.”
This was the hottest June on record, setting the stage for the monsoon. The heat persisted, but the storm activity did not.
This high-pressure system can stall over certain parts of the Southwest and bake the area below rather than settling in its optimal location over the Four Corners to trigger storms. If the high-pressure system makes it to the Four Corners, everything below it is primed for storm activity, according to Saffell.
Phoenix is at a lower elevation, and when the high-pressure system stalls overhead, it compresses air and triggers higher temperatures.
This compounds the effects of global warming and the urban heat island in the city, when buildings, roads and infrastructure absorb and re-emit the sun’s heat at night.
Storms during the monsoon can bring a reprieve from the heat, sometimes dropping the temperature 20 to 30 degrees immediately after a storm, according to Saffell.
“When we have more thunderstorm activity, that cools us off,” she said. “Hotter temperatures mean usually we’re just not getting as many thunderstorms.”
As the monsoon ends, the heat will continue, especially as Arizona heads into two of its driest months in October and November. Phoenix experienced its latest day over 110 degrees when Phoenix Sky Harbor reached 113 on Sept. 25, also shattering the daily record.
With triple digits forecast through the weekend, records could be broken once again.
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What does a dry monsoon mean for water, wildfires?
Although the monsoon season officially ends on Monday, monsoon conditions ran out before the calendar season did.
“The dew points have been dropping, it’s been drying out,” Saffell said. “It’s a way of understanding if there is enough water in the atmosphere that can produce a thunderstorm. I’m not expecting to get any more precipitation for September.”
While this monsoon will be one of the driest, Phoenix’s water supplies remain in fairly good condition.
“Even with a dry monsoon season, that doesn’t necessarily mean bad things for the Valley because our water supply is largely reliant on winter precipitation versus summer precipitation,” said Laura Hodgens, senior meteorologist for Salt River Project.
Hodgens said SRP’s gauges trended below average for precipitation in the watershed but were still relatively close to normal values. About 80% of SRP’s water supply comes from the winter months.
But dry conditions contributed to wildfire activity this year, according to Saffell. There was a 60% increase in wildland fire acres burned so far this year during the same time frame last year.
When the monsoon brings precipitation to wildlands, it keeps the vegetation moist. If a fire hits moist vegetation, it won’t burn as readily. Following one of the driest and hottest monsoons on record, there is continued wildfire risk across the state.
“When we’re hotter, it dries out our vegetation. So that makes it a little bit more susceptible to wildfire activity,” Saffell said. “It’s just important to recognize it’s hot, it’s dry. We want to pay attention to what’s going on around us.”
Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic and azcentral.com. Email her with story tips at hayleigh.evans@arizonarepublic.com.
This article originally appeared on Arizona Republic: Seventh-driest monsoon ends with a September heat wave in Phoenix
