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.
Since May 13, the NWS forecast for July to September has shown that this summer in Phoenix has a 40% chance of a wetter than normal a 27% chance of summer being drier than usual. The baseline for Phoenix is 2.7 inches of precipitation.
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.
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 inches4. 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.
