Tropical Storm Mario Brings Monsoon Storms to Arizona This Week
Phoenix, Arizona – Moisture from the remnants of Tropical Storm Mario is moving into the Southwest, setting up for another series of monsoon storms as the season comes to a close. The official end of the monsoon season is on September 30, and Mario’s tropical plume is expected to increase storm chances across Arizona and southeast California through September 19.
Although Mario will not make landfall, it is sending a surge of humidity into the region, raising the likelihood of storms. “We’re going to see increasing moisture starting in the middle of the week,” said Matt Salerno, lead meteorologist with the National Weather Service in Phoenix. “It’s going to feel muggy outside again. We’ll start to see rain chances increase.”
Moisture levels are rising, measuring 150% to 200% above normal, which can lead to heavy downpours if storms develop. Areas in western Arizona and southeast California are expected to experience storms first, with rain chances moving east into south-central Arizona by September 18. In Phoenix, the probability of storms will range from 40% to 60% from Thursday afternoon to Friday morning. Some neighborhoods could receive over an inch of rain, while others may not see any.
Localized flash flooding, strong winds, and blowing dust are also potential threats. Such storms are not uncommon; on September 8, 2014, a similar occurrence doused Phoenix with a record-breaking 3.3 inches of rain in a single day, the highest amount in over 115 years of record-keeping. However, the atmosphere is expected to dry out over the weekend, with scattered showers possible but coverage limited to about 20%.
The increase in moisture and cloud cover may bring temperatures down into the 90s, providing a welcome break from earlier triple-digit heat. “Overall, the pattern is going to be these batches of rain that move through the region, as well as cooler temperatures,” Salerno said.
As of now, Phoenix’s Sky Harbor has recorded only 0.68 inches of rain this monsoon season, falling short of the seasonal average of 2.18 inches by this time and the total average of 2.75 inches for the entire season. This makes 2025 the eighth-driest monsoon season to date, with Phoenix likely to conclude below normal rainfall levels. “Hopefully we pick up at least a good amount of rain from the next few days so we can make up some ground, but it looks like we’re still going to fall short overall,” Salerno added.
Residents are encouraged to share their storm videos and photos for potential use on azcentral.com.
