The forecasted “Super El Niño” is expected to delay the start of Southern Arizona’s monsoonal season but by August it could trigger heavier, more intense rainfall, severe flash flooding, and unusually high humidity during its peak. While El Niño historically weakens global monsoons, its impact on the Desert Southwest creates unique atmospheric shifts for the June 15 to September 30 season.1 Climate experts from the National Weather Service and the University of Arizona predict the season will unfold across three distinct phases: 2
A Delayed and Drier Onset: Early in the summer, El Niño’s atmospheric patterns alter the subtropical jet stream, creating persistent westerly winds across the Southwest.
Moisture Suppression: These westerlies act as a wall, driving out early moisture from the south and delaying the typical shift to monsoonal wind patterns.
Increased Fire Risk: A slower, drier start to the monsoon prolongs the summer dry spell, elevating the risk of wildfire ignition from dry lightning storms.
HIGH-INTENSITY PEAK (August into September)
Tropical Cyclone Activity: The incredibly warm ocean temperatures of a Super El Niño fuel severe hurricane activity off the Pacific coast of Mexico.
Tropical Moisture Pumps: While the hurricanes themselves rarely hit Southern Arizona directly, they act as massive atmospheric pumps, steering heavy tropical moisture straight into the Desert Southwest.
Rain Bombs and Flooding: As this extra moisture collides with the desert heat, it increases the likelihood of high-intensity storms, widespread flash flooding, severe dust storms, and heavy rainfall that could reach up to 150% of normal averages in some areas.
A SHIFT TO MOIST HEAT (after September)
High Humidity: Southern Arizona is famous for its dry heat, but the influx of Pacific moisture will cause humidity levels to skyrocket.
Stubbornly High Temperatures: Even with localized cloud cover and rain mitigating the most extreme temperature spikes, daily highs will remain brutally hot—frequently ranging between 100°F and 115°F. The added moisture will result in a heavy, oppressive “moist heat” rather than a dry one.