Dew Point Rule: Monsoon 2025 starts!

Officially, Monsoon 2025 started on June 15th; however, before 2008, the monsoon did not begin in Phoenix until the daily average dew point was 55°F or higher for three consecutive days. This was known as the "dew point rule" and is still a fun concept to track.

Well, guess what, the dew point average at Phoenix Sky Harbor was 58º on July 2nd, 64º on July 3rd, and 59º on July 4th. As a result, Monsoon 2025 started using the dew point rule on July 2nd, which is a tad early, as the average start date is July 7th. The earliest start date was June 17, 2000, and the latest was July 25, 1987.

For comparison, last year, Monsoon 2024 started on June 21st.