Arizona Monsoon 2026: Phoenix Rainfall by the Numbers

Arizona's monsoon season runs June 15 through September 30 — fixed dates the National Weather Service adopted in 2008. Before that, the monsoon was only declared once Phoenix logged three straight days with an average dewpoint of 55°F or higher. It was a meteorologically honest rule, but a confusing one: the “start date” jumped around the calendar every year, and the public could never plan around it. The fixed window fixed that.

The calendar dates and the actual storms are two different things. The monsoon is a seasonal wind shift — high pressure parks over the Four Corners in mid-summer and pulls tropical moisture north out of the Gulf of California and the eastern Pacific. That moisture usually doesn't arrive in force until early-to-mid July. June 15 to early July is often hot and bone-dry; the real action — towering thunderstorms, dust walls, flash flooding — tends to peak from mid-July through August.

On September 8, 2014, Phoenix Sky Harbor recorded 3.30 inches of rain in a single day — the wettest day in the station's monsoon record, and one of the wettest calendar days in city history. The deluge came from the remnants of Hurricane Norbert, which pumped a deep plume of tropical moisture into Arizona. Freeways turned into rivers, drivers were rescued from submerged underpasses, and the city picked up more rain in a morning than it normally gets in three months.

That day is the perfect illustration of how Phoenix's monsoon works: the season's total often hinges on one or two extreme events. The next-biggest monsoon days in the record — September 5, 1970 (2.43″) and July 28, 1984 (1.90″) — also clustered into the wettest seasons. Miss those, and you get a 2023.

If you want monsoon rain in Arizona, go to Tucson. Tucson averages 5.95 inches of monsoon rain — more than double Phoenix's 2.56 inches, despite sitting only 115 miles southeast. The difference is geography: Tucson is higher in elevation and sits closer to the Gulf of California, the monsoon's primary moisture pipeline, so it taps the tropical air earlier and more reliably each summer.

Tucson's ceiling is higher too. Its wettest monsoon on record — 12.80 inches in 2021 — would be an almost unimaginable year for Phoenix. Even Tucson's driest monsoon in our record (1.62″ in 2020) beats Phoenix's long-term average. When people say “the monsoon was a bust in Phoenix,” it's often still been a respectable season 100 miles south.

You can pull the same daily history for either city — or any of 50+ U.S. cities — and check the rain on any past date with our Phoenix weather history and Tucson weather history pages, both built on the same 139-million-record NOAA database.

For 2026, the official signals lean wet. The NWS Tucson monsoon outlook issued May 21, 2026 leans above-normal for both Phoenix and Tucson, and NOAA's Climate Prediction Center favors a wetter-than-normal — and hotter-than-normal — monsoon across the Southwest.

The wildcard is the developing 2026 El Niño. Here's the honest caveat the cheerful forecasts sometimes skip: there is no reliable correlation between El Niño and Arizona monsoon rainfall. Some El Niño summers are wet, some are dry. What El Niño does do is increase eastern Pacific tropical storm activity, which raises the odds that a decaying tropical system — like Norbert in 2014 — sweeps moisture into Arizona late in the season. That's the mechanism most likely to push 2026 toward the wet end. For the broader picture, see our El Niño 2026 forecast.

One thing the monsoon reliably does, wet year or dry: it breaks the early-summer heat. Phoenix spends June grinding through triple-digit afternoons that routinely spike past 110°F — see our Southwest heat wave 2026 analysis and where Phoenix lands among the hottest cities in America — and the first monsoon storms are what finally knock daytime highs down and lift the overnight humidity.

Monsoon rain is welcome; the storms that deliver it are not always gentle. The same outflow winds that build thunderstorms also kick up haboobs — towering walls of dust that can drop highway visibility to zero in seconds. And because desert soil sheds water rather than absorbing it, even a modest cloudburst can trigger deadly flash flooding in normally dry washes miles from where the rain fell.

Dust storms are the monsoon's most dangerous side effect — and Arizona gets the biggest ones in the country. We cover when they hit, why they form, and the largest on record in our companion guide to Arizona dust storms and haboobs.