Moisture will continue to fuel monsoon thunderstorms through the middle of next week

Tucson residents should expect more monsoon thunderstorms in the coming days, but the most active weather is likely to remain south and east of the city. Forecasters say moisture will stay in place through the middle of next week, bringing scattered storms to Southern Arizona. Tucson and nearby communities may see isolated thunderstorms, while areas in Southeast Arizona face a greater chance of heavy rain, flash flooding, strong wind and blowing dust.

High temperatures are expected to remain in the mid to upper 90s through the weekend, with overnight temperatures in the mid 70s. The combination of daytime heat and persistent monsoon moisture will continue to support storm development, although the distribution of rainfall will be uneven. Some neighborhoods could receive little or no rain while nearby areas see a brief but intense downpour.

The weather pattern is expected to become more favorable for Tucson storms next week. High pressure is forecast to shift east, allowing thunderstorms to develop farther north than they have recently. That change could improve rain chances across Tucson and surrounding communities, although storms will still be isolated and difficult to predict at the neighborhood level.

A more immediate concern is Southeast Arizona, where the National Weather Service issued a Flood Watch for Graham, Greenlee, Cochise and Santa Cruz counties from noon Monday through midnight Monday. The greatest threat is expected east and south of Tucson, particularly in Cochise and Santa Cruz counties. An upper level disturbance moving in from New Mexico, combined with abundant monsoon moisture, is expected to produce a more active round of showers and thunderstorms.

Forecasters warned that some storms could drop 1 to 3 inches of rain in localized areas. Much of the region remains saturated after repeated storms during the previous week, leaving soils with limited capacity to absorb another round of rainfall. That means water could run off quickly, increasing the danger of flash flooding in washes, low lying areas and locations with poor drainage. Another chance for heavy rain is possible Tuesday, especially across the eastern half of Southeast Arizona, though confidence in that forecast is lower.

Storms also could bring hazardous conditions beyond flooding. Thunderstorms in the Gila River Valley and San Simon Valley may produce wind gusts of 40 to 45 mph and areas of blowing dust. Aviation forecasters cautioned that erratic winds in those valleys could reach 35 to 40 knots. For drivers, sudden reductions in visibility, water covering roadways and rapidly changing wind conditions could make travel difficult, particularly during the strongest storms. The weather service said visibility in the heaviest downpours could fall to between 3 and 5 miles.

The moisture affecting Arizona is part of a broader pattern across the Southwest. Tropical Storm Marie, located hundreds of miles southwest of San Diego before being downgraded to a post tropical cyclone, sent tropical moisture into California and parts of the Southwest. A dip in the jet stream over the northwestern United States is helping draw some of that moisture toward the Four Corners and Southern California, strengthening the southwest monsoon pattern. Farther east, the added moisture may increase the risk of flash flooding in southern Nevada, Utah and northern Arizona.

Those wider impacts have already included unusual September rain in Southern California. Los Angeles received 0.6 inches on Sunday, its first measurable rain there since April and its wettest September day since 2015. Marie also contributed to heavy rain in the San Bernardino Mountains and High Desert. The storm is expected to remain offshore, but its swells have prompted high surf and coastal flood advisories from Los Angeles to San Diego, where some waves could exceed 10 feet. More than a dozen homes in Long Beach were evacuated after damage to a seawall and boardwalk raised concerns about structural safety.

The moisture driven storm pattern also comes with risks in desert and canyon country. Thunderstorms fueled by Marie and an upper level trough are expected to raise the threat of flash flooding in places such as Zion Canyon and the Grand Canyon. That warning follows deadly flooding at Grand Canyon National Park the previous week, which killed two people and led to dozens of rescues. In Arizona, Nevada and Utah, officials are particularly concerned about sudden runoff in dry washes, narrow canyons, slick rock areas, poor drainage zones and recent burn scars. For Tucson residents, the main takeaway is that monsoon activity is not ending soon. Storm chances should continue through the weekend, increase somewhat next week, and require close attention to local warnings, especially for anyone traveling south or east of the city.