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.

Phoenix started the summer tracking near-record dry. Through August 17, Sky Harbor had managed only 0.65 inches since June 15, a total the National Weather Service said had been beaten to the dry side just once, in 1921. But the monsoon finally woke up. A run of storms in late August and the first days of September lifted Phoenix to 1.41 inches across 10 wet days through September 3 — still about a quarter below its normal pace for the date (near 1.9 inches), but well clear of record territory. It is shaping up as a dry-ish, unremarkable year, not the near-failure of 2023 (0.15 inches).

Tucson tells a healthier story. It jumped out to a wet start in early July and kept pace: 4.97 inches over 21 wet days through September 3, running slightly ahead of its normal pace (about 4.6 inches) and on track for a near-normal season. Tucson out-rains Phoenix better than three-to-one this summer — exactly the geography the 70-year record shows, since it sits higher and closer to the Gulf of California moisture pipeline.

The takeaway with the season nearly over: Phoenix's slow start recovered enough to dodge the record books but not enough to reach average, while Tucson quietly banked a normal monsoon. For Phoenix to hit even its modest 2.56-inch average, September would have to deliver far more rain than the month typically sees — possible only if a decaying eastern-Pacific tropical system swings moisture north. We update these figures from the daily NOAA feed.

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 favored a wetter-than-normal — and hotter-than-normal — monsoon across the Southwest. As of late August, that outlook is verifying only half right: the heat showed up, but the rain did not, at least for Phoenix, which is running one of its driest monsoons ever. Tucson landed close to normal. It is a clean example of how little skill seasonal monsoon outlooks actually carry — a "lean above-normal" is a tilt of the odds, not a forecast, and in 2026 the tilt busted for the Valley.

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.