Arizona Monsoon

During the monsoon, or summer thunderstorm season, Arizona experiences more severe weather than many other states. On rare occasion, a severe storm may spawn a tornado. More often, high winds, dust and severe downpours resulting in flash floods are common monsoon occurrences.

In Phoenix, the monsoon is considered to have started when we have three consecutive days when the dew point averages 55 degrees or higher. The 55 degree threshold should be viewed as a guideline for the beginning of the monsoon, and not a hard and fast rule.

More About Phoenix Monsoon

• The average starting date of the monsoon in Phoenix is July 7.
• The average ending date of the monsoon is September 13.
• The earliest start date for the monsoon was June 16, 1925.
• The latest start date for the monsoon was July 25, 1987.
• The average date of the first break in the monsoon is August 16.
• The average total number of monsoon days (where a monsoon day is considered one with an average dewpoint of 55 degrees or higher) is 56.
• The greatest number of monsoon days was 99, recorded in 1984.
• The fewest number of monsoon days was 27, recorded in 1962.
• The greatest number of consecutive monsoon days was 72, from June 25 through September 4, 1984. This was also the greatest number of consecutive days with dew points of 60 degrees or higher.
• In Phoenix, normal rainfall during July, August and September is 2.65 inches.
• The wettest monsoon occurred in 1984 when we had 9.38 inches of rain.
• The driest monsoon occurred in 1924 with only 0.35 inches.