When Is Monsoon Season in Arizona? Dates, Hazards, and What to Expect

Arizona’s monsoon season runs from June 15 through September 30 every year, with the most active stretch usually falling in July and August. If you are new to the desert, the monsoon can be a surprise. One afternoon the sky is clear, and the next a wall of dust or a sudden downpour rolls across the Valley. Here is what the season is, why it happens, and what to expect while it is here.

When is monsoon season?

The official dates are June 15 through September 30. The National Weather Service set that fixed window in 2008 to make the season easier to track and prepare for. Before then, the start was tied to dew points, once the air stayed humid enough for three days in a row. The calendar dates replaced that to keep things simple.

In practice, the first couple of weeks are often quiet. Storm activity usually picks up in early to mid July, once enough moisture is in place, and August tends to be the busiest month before things wind down through September.

Why Arizona gets a monsoon

The monsoon is driven by a seasonal shift in the wind. Through the spring, our winds generally come from the west and stay dry. As the land heats up over Mexico and the Southwest in early summer, a large area of low pressure forms and changes that pattern, pulling moist air up from the Gulf of California and the eastern Pacific.

You can often feel the change before you see it. Dew points climb from the single digits into the 50s, the air turns humid and sticky, and that added moisture is the fuel for afternoon and evening thunderstorms. It is the same basic pattern that gives much of the Southwest its summer storms.

What to expect during the season

Monsoon storms are short, intense, and can turn dangerous quickly. The main hazards to know are:

• Dust storms, or haboobs. Walls of blowing dust can drop visibility to near zero in seconds.
• Microbursts. Powerful downdrafts can produce straight-line winds over 100 miles per hour, strong enough to tear off roofing and topple trees.
• Flash flooding. Rain falls faster than the dry ground can absorb it, and just six inches of moving water can knock a person off their feet. Never drive into a flooded wash.
• Lightning and hail. Both are common with monsoon storms and can cause damage of their own.

These storms often hit in the late afternoon and evening, and they can arrive with very little warning.

How long do monsoon storms last?

Individual monsoon storms are usually short. The heaviest rain often lasts anywhere from about 15 minutes to a couple of hours, and the most violent wind, like a microburst, may only last a few minutes. What makes the season feel relentless is that storms tend to arrive in waves, so one can move through and another can build behind it over the same afternoon and evening.

They also form fast. A morning that starts out calm can turn stormy by late afternoon, sometimes in a matter of hours, so it pays to keep an eye on the forecast and move quickly once a storm is on the way.

What the monsoon means for your home

For homeowners, the monsoon is the time of year when water and wind damage are most likely. Driving rain finds gaps around the roof and windows, flash flooding can push water inside, and high winds can lift tiles or bring down a branch. If water does get in, catching it early matters, since moisture left in walls and floors can lead to mold within a day or two.

Knowing what the season brings makes it far less stressful to ride out. Even so, a strong storm can still catch you off guard. If wind or water leaves damage behind anywhere in the Phoenix Valley, Restore Master is here to help with storm damage cleanup and repairs whenever you need it.