Monsoon

The monsoon is a seasonal shift in wind direction, not a single storm. University of Arizona Cooperative Extension describes a high-pressure zone parking near the Four Corners and spinning clockwise, dragging moisture north from the Pacific and Gulf of Mexico. Arizona State Parks puts the season at June 15 through September 30, and notes July and August bring more than half the precipitation the state sees in a year.

What arrives is not steady rain. A cell builds in the afternoon, collapses, and shoves a wall of wind and dust ahead of it. Maricopa County reports that one to three dust storms reach the Phoenix area in a typical year, lasting minutes to an hour. That dust packs into scuppers, valleys, and gutters. Then rain hits sideways, testing every roof edge, window head, and wall penetration.

Volume is the second problem. Storms drop hard on ground that absorbs almost none of it, so runoff sheets rather than soaks. Maricopa County's warning is blunt: six inches of moving water can knock a person off their feet, and two feet can float a car. That is why finished grade and swales matter more here than the annual rainfall total suggests.

The season also moves your schedule. Grading stops when the subgrade is too wet to compact. Roofing stops mid-storm, and a house that is not dried in stays exposed. Fresh stucco needs to cure without a downpour running down it. For example, a builder starting a Cave Creek home in April aims to finish the pad, drainage, and dry-in before mid-June, then plans July and August as slower months.

One thing owners misread: most days inside the window are dry, so this is not a rainy season the way a Gulf Coast summer is. It is a few violent hours scattered across three and a half months. That makes it a detailing problem. Your drainage plan and your flashing either hold for those hours or they do not.