Unlike the 2019 monsoon season where it was a very late start and for a moment very brief, the projection here at Arizona Weather Force is calling for an Above Average Monsoon Season so read on for details …
The atmospheric profile with this is because I have issued a La Nina Watch. This La Nina I expect to develop by Summer and last for a year. La Nina tends to lead to a below average Eastern Pacific Hurricane Season and this is a pretty big source for moisture traveling northward into Arizona. Unlike last July and August, this year will have numerous days of monsoon activity those months and I expect it to be very active.
We won’t rely on the Eastern Pacific this year, but we will rely on the Atlantic Hurricane Season. The Atlantic Ocean and Gulf of Mexico is extremely warm right now, warmer than average. These waters will work with less shear and promote an above average Atlantic Hurricane season. As a result, the westward movement through the Gulf of Mexico and Jamaica on an elongated Eastern USA Ridge will shove both moisture and upper level dynamics into Mexico and then to Arizona as it catches the monsoon ridge.
This year, the monsoon ridge will most likely develop over the four corners, which is the nominal position for a good monsoon across the state. Many years previous, with drier conditions, the monsoon ridge developed over Utah and Nevada, which blocked Gulf of Mexico moisture and sent a lot of activity into Southern California. This year I do not see much of that on average.
My calculation for Tucson is 6.5 inches of rain on average with a median of 6.5 to 7.5 inches expected from June 15th through September 15th, which makes it an above average season.