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October is here and cooler temperatures are just around the corner. That means the Valley’s monsoon season is at its end. And as forecasters predicted, there was a fair amount of rainfall.
Despite the scorching heat brought on by summer in the desert, one of the marks of Arizona summers is the monsoon – a furious rainstorm caused by a reversal in weather patterns.
In the winter, jet streams carry rain west to east from the Pacific Ocean into Arizona. But during the summer, the storms come from the south and west, typically establishing a high-pressure area over the Four Corners region and bringing varied amounts of rainfall year by year.
According to the National Weather Service, monsoon season runs from June 15 to Sept. 30 – the hottest months of Arizona summer. On average, about half of the yearly rain in Phoenix falls in this period.
At the beginning of summer, the NWS forecast for July to September predicted that this summer in Phoenix had a 40% chance of a wetter-than-normal season and a 27% chance of the summer being drier than usual. The baseline for Phoenix is 2.7 inches of precipitation.
As it turns out, that’s almost exactly how much rainfall we got. NWS data on Tuesday showed that during the monsoon months, Phoenix saw about 2.76 inches of rain.
While that figure is about average, it’s far more than in years past. The monsoons of 2024 and 2023 were among the driest in Phoenix history, seeing only 0.74 and 0.15 inches, respectively. This year’s monsoon was the wettest since 2021, when the Valley got 4.2 inches, and the second-wettest since 3.29 inches fell on the Valley in 2015.
This talk about averages might have you wondering: What were the rainiest monsoon seasons the Valley has ever seen? What were the driest?
NWS data offer the answer to both. Here are the five wettest and driest monsoon seasons in Phoenix history.
National Weather Service
Wettest Phoenix monsoon seasons
5. 1896: 7.2 inches of rain. One of the wettest years in Phoenix history, 1896 is the first year that precipitation was recorded.
4. 1939: 9.3 inches
3. 1946: 7.5 inches
2. 1911: 9.3 inches. Back in Phoenix’s early days as an agricultural town, it experienced the rainiest 24 hours in its history. About 5 inches of rain fell on the desert on July 2, 1911.
1. 1984: 9.6 inches. The rainiest season in Phoenix’s recorded history is also the record-holder for most monsoon days (when the dewpoint is over 55 degrees) with 99.
The only monsoon season after 1984 that cracked the top 10 list is 2014, when Phoenix saw 6.3 inches of rain.
Driest Phoenix monsoon seasons
5. 1993: 0.61 inches
4. 1932: 0.61 inches
3. 1914: 0.51 inches
2. 1924: 0.35 inches
1. 2023: 0.15 inches. This was also the hottest summer on record in Phoenix, with an average temperature topping 97 degrees.
The sixth-, seventh- and eighth-driest years were 2019, 2007 and 2024, respectively. Each saw less than three-quarters of an inch of rainfall.
