Here’s what you need to know about official start of Arizona monsoon season

Jun 13, 2024, 4:35 AM

Lightning strikes during a monsoon storm on July 21, 2022, near Mayer, Arizona. The Arizona monsoon...

Lightning strikes during a monsoon storm on July 21, 2022, near Mayer, Arizona. (Photo by Mario Tama/Getty Images)

(Photo by Mario Tama/Getty Images)

PHOENIX – Saturday is the first official day of the Arizona monsoon season, but what exactly does that mean?

The season runs from June 15 to Sept. 30 each year, but those dates don’t necessarily indicate the greatest likelihood for monsoon storm activity, local climate expert Randy Cerveny explained.

“We kind of set it up like what they do with hurricane season. When the hurricane season starts at the start of June, it’s not like suddenly you’re going to get a hurricane on the first day,” Cerveny, a professor of geographical sciences at Arizona State University, told KTAR News 92.3 FM on Monday.

“They’ve set it up now so that it allows time for people to be aware of how monsoon thunderstorms can impact them.”

When do Arizona monsoon storms usually start?

Cerveny said the Phoenix area typically gets its first storms of the monsoon season in the first week of July.

“People have to realize that it doesn’t start out wet, that the first few weeks of our monsoon are dry,” he added. “That means a lot of lightning, a lot of wind, very little rain, and those are the perfect recipes … for wildfires.”

2023 was Phoenix’s driest monsoon season on record, with the first rain not coming until Aug. 17 and a final total of just .15 inches.

The dry conditions contributed to a brutally hot summer. In fact, Phoenix actually endured the hottest month ever recorded in a major U.S. city in July 2023.

Will Phoenix see a repeat of 2023’s historically dry monsoon season?

Will it be wetter in 2024? Cerveny thinks so.

“We’re not looking at an incredibly dry monsoon this year,” he said. “We’re probably not looking at a record monsoon in terms of wetness, either. It’s probably going to be normal.”

Cerveny said meteorologists are seeing signs that monsoonal moisture will start moving north from Mexico later this month, indicating normal weather patterns for this time of year.

“What we should start to see within the next week or so is good thunderstorms that are building up along the west coast of Mexico,” he said. “And over the next few weeks, those thunderstorms are going to slowly percolate their way northward. The start of the monsoon is when that moisture that charges up those thunderstorms starts working its way up into Arizona.”

What does summer rainfall mean for drought?

While precipitation is always welcome in the desert, Cerveny noted that monsoonal rainfall doesn’t have much impact on drought conditions.

“It does contribute nastily to wildfires, but the moisture that we need to break droughts is more wintertime rainfall and snowfall rather than the summer months,” he said.

According to the U.S. Drought Monitor report for June 4, 23.17% of Arizona is experiencing moderate or worse drought. Last year at this time, after a wetter-than-normal winter, it was only 1.46%.

Cerveny explained that monsoon thunderstorm rainfall tends to run off quickly rather than soaking into the ground or filling reservoirs.

Phoenix typically receives 2-3 inches of rain each monsoon season and 7-8 inches total per year.

“So, it doesn’t contribute a whole lot to our water supply,” Cerveny said of monsoonal precipitation.

Although early signs are pointing toward a normal season, Cerveny cautioned that monsoons have the tendency to confound forecasters.

“The monsoon is a tricky beast; it likes to confuse us as much as possible,” he said. “We have to kind of wait to see how the upper atmosphere pattern sets up and then we can start to figure out whether this is going to be a wet one or a dry one.”

KTAR News 92.3 FM’s Jim Cross contributed to this report.

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Here’s what you need to know about official start of Arizona monsoon season