Officially, Monsoon 2022 started on June 15th and will end on September 30th, but before 2008, the dew point rule was used. The rule was that the monsoon started in the Valley of the Sun if the daily average dew point in Phoenix was 55º+ for three days in a row.

Some people (myself included) still like to track the dew point, and it is was great excitement to say that today (June 27th) will likely be the third day in a row with a daily average dew point of 55º+ at Phoenix Sky Harbor (57º on June 25th, 57º on June 26th, and estimated to be around 61º on June 27th). This means the monsoon, using the dew point rule, started on Saturday, June 25!

This ties as the 5th earliest start to the monsoon using the dew point rule.

Top five earliest starts:
1) June 17, 2000
2) June 19, 1958
3) June 21, 2001
4) June 23, 1954
5) June 25, 1984, 1999, 2022