Has the Arizona monsoon arrived early?

PHOENIX — The smell of rain returned to the Sonoran Desert in early June, and scattered storms have already doused parts of Arizona and New Mexico. For many residents across the Southwest, the thunder and rainfall that rolled through felt like a welcome—and familiar—summertime weather setup: the monsoon.

But despite the early showers, this is not the start of the monsoon. Why?

Well, the monsoon isn’t just about rain.

The North American Monsoon (NAM) is a seasonal shift in the large-scale weather pattern that brings a dramatic increase in moisture and rainfall to the Southwestern United States, typically from mid-June through September. It refers to this seasonal shift, not individual storms. The monsoon affects Arizona, New Mexico, and parts of surrounding states, transforming our dry deserts into brief oases of green.

But what sets the monsoon apart from a mere rainstorm is a consistent and large-scale pattern shift in atmospheric circulation.

The word monsoon is actually derived from the Arabic word mausim, which means “season.” So, it’s not just about one storm or a few days of rain. It’s about a seasonal transition in wind direction and humidity that persists.

This year, parts of Arizona and the broader Southwest were soaked by localized thunderstorms and convective showers in early June, a rarity for this time of year in Arizona. Some areas recorded several inches of rain or more, and social media buzzed with lightning videos and rooftop downpours.

However, these early rains were not monsoonal in origin.

These storms were the result of upper-level disturbances and residual moisture from tropical storm Alvin off the coast of Mexico, not the true monsoon flow. Until we see a substantial shift in the pattern that brings more of a south-to-southeast flow bringing in tropical moisture from the Gulf of California and Mexico, it’s not the monsoon.

In other words, early June rains were great, but more like a dress rehearsal than opening night.

The National Weather Service no longer declares a monsoon “start date” based solely on dew point temperature, as it once did prior to 2008. Instead, it recognizes June 15 as the climatological start of the monsoon season—a standardized date used for tracking statistics, not atmospheric reality.

But for meteorologists, the actual beginning hinges on a sustained shift in the upper-atmospheric winds and the consistent presence of high dewpoints (typically above 55°F in Phoenix, for example).

As of early June, the subtropical ridge—an area of high pressure that plays a central role in steering moist air northward—remains in flux.

When the monsoon begins, we’ll look for that ridge to be more or less locked into place over the Four Corners region.

The early rains may have whetted the desert’s appetite, but they don’t necessarily signal a wetter season to come. In fact, early storms can sometimes give a false impression, especially if followed by a prolonged dry spell.

The Climate Prediction Center’s seasonal outlook for July-September predicts a 33-50% chance of above-average rainfall across much of Arizona. But the timing, frequency, and coverage of monsoonal storms will remain difficult to forecast week to week.

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That’s because monsoon typically brings rain in surges. We might get a strong start, then a long lull. Or it could ramp up late and finish strong. What matters is the overall pattern and how it evolves through the season.

Yes, it rained in June. But no, the monsoon hasn’t officially begun.

The North American Monsoon is more than a few thunderstorms—it’s a full atmospheric shift that brings weeks of humidity, heat, and dramatic weather. Until that pattern locks in, early showers are just that: early.

So keep your umbrellas handy, but don’t cross “monsoon begins” off the calendar just yet.