Tropical Storm Mario was a compact tropical cyclone that affected parts of western Mexico and the Southwestern United States in September 2025. The fifteenth named storm of the 2025 Pacific hurricane season, Mario developed from a tropical wave that moved off the coast of Central America on September 8. The wave turned northwestward developed into a tropical storm on September 12. However, an unfavorable environment for intensification caused Mario to open up into a trough early on September 13.
The remnants of Mario moved westward and redeveloped into a tropical storm on September 14. As Mario moved west-northwestward to northwestward, it began to intensify. By September 15, Mario attained its peak intensity with maximum sustained winds of and a minimum central pressure of . Shortly after, Mario began to weaken and degenerated into a remnant low by September 16. Mario then dissipated on September 18.
In anticipation of Mario, the Government of Mexico issued a tropical storm watch for coastal portions of Michoacán. Remnant moisture from Mario brought heavy rainfall that triggered flash flooding and mudslides across portions of Baja California Sur and the Southwestern United States. In the former, more than 60 homes were damaged by floodwaters. Overall, Mario caused two deaths and US$40.7 million worth of damage.
On September 8, a tropical wave emerged off the coast of Central America. The wave began moving westward and an area of low pressure formed within the wave on September 10. The low turned northwestward and began to organize. On September 11 at 06:00 UTC, the system acquired a center of circulation, developing into a tropical depression while situated southeast of Acapulco, Mexico. The depression moved west-northwestward due to the influence of a ridge situated over northern Mexico and Texas. On September 12 at 00:00 UTC, the depression strengthened into a tropical storm and was named Mario, while located southeast of Acapulco. However, moderate northeasterly wind shear, dry air intrusions, and land interaction caused Mario to open up into a surface trough by September 13 at 00:00 UTC.
While turning to the west, an area of low pressure formed within the remnants of Mario later that day. Convection within the system began to reorganize, and Mario redeveloped into a tropical depression by September 14 at 06:00 UTC. By 12:00 UTC the same day, Mario restrengthened into a tropical storm while situated south of the Baja California Peninsula. Mario began moving westward to west-northwestward under the influence of a ridge over northern Mexico and a trough offshore the Baja California Peninsula. Within an environment characterized by warm sea surface temperatures and low vertical wind shear, Mario began to intensify. On September 15 at 12:00 UTC, Mario reached peak intensity, with maximum sustained winds of and a minimum central pressure of while located southwest of the Baja California Peninsula. Mario then moved into an environment with cooler waters and higher vertical wind shear. Mario began to quickly weaken and all convection within the storm began to collapse. By September 16 at 12:00 UTC, Mario degenerated to a remnant low while moving northwestward and slowing its forward motion speed. By September 18 at 12:00 UTC, the low degenerated to a trough of low pressure and dissipated, while situated west of Cabo San Lazaro, Baja California Sur.
On September 12, the government of Mexico issued a tropical storm watch from Lázaro Cárdenas, Michoacán to Punta San Telmo, Michoacán. Civil Protection personnel were deployed to coastal portions of the state. The ports of Lázaro Cárdenas, Zihuatanejo, and Acapulco were closed to boat traffic. Classes for all grades in coastal regions of Guerrero and Michoacán were cancelled in anticipation of Mario. A green emergency alert, signifying a low level of danger, was issued for Jalisco. A blue alert, signifying a minimal level of danger, was issued for Guerrero and Oaxaca. An Independence Day dance event in Mulegé was cancelled.
While Mario made its closest approach to the southwestern coast of Mexico, more than of rain was reported in a 24-hour period across portions of Guerrero and Colima. A peak wind gust of was reported at the Acapulco International Airport. Heavy rainfall from the precursor of Mario was reported in Chiapas, resulting in the inundation of fifteen homes and 27 neighborhoods. In Guerrero, heavy rains caused flooding and landslides while gusty winds downed trees and utility poles, resulting in minor electrical and communication outages.
When Mario degenerated to a remnant low, a trough advected remnant moisture from Mario northward into Baja California Sur. Across portions of the state, heavy rainfall that triggered flash flooding was reported. In San Ignacio, flooding was reported in at least six neighborhoods and 62 homes. Around 250 families were left homeless as a result. Two shelters were opened for 20 residents whose homes suffered severe flood damage. Floodwaters washed out two portions of the Transpeninsular Highway in San Ignacio, trapping a tank truck and leaving the community isolated for three days. Several people were rescued after floodwaters trapped two vehicles. Three fallen utility poles were reported, causing disruptions to electrical service in Ciudad Constitución. Power outages affected operations at ten schools across Mulegé. Flooding caused sewage to flood onto streets across Los Cabos. In San Ignacio, a 37-year-old man was killed by lightning.
In anticipation of the remnants of Mario, portions of the Southwestern United States were placed under a slight risk of excessive rainfall. Flash flood watches and warnings were issued throughout Central and Southern California. Forecasters warned that flooding could be exacerbated by the presence of burn scars. Additionally, forecasters noted a moderate fire risk for California, warning that lightning could spark potential fires.
As the remnants of Mario passed through Southern California, their primary effect was heavy rainfall that triggered flash flooding and mudslides. In Running Springs, of rainfall was recorded. Ridgecrest recorded a rainfall total of . A wind gust of was reported in Imperial County. Imperial Irrigation District reported the storm downed more than 100 utility poles, leaving nearly 7,000 customers without power. In San Bernardino County, fourteen homes were damaged and an additional three homes were destroyed by mudslides. In the San Bernardino Mountains, debris flows trapped at least six vehicles, resulting in the rescue of ten people. In Cabazon, two people were injured in a seven-vehicle collision as a result of hazardous driving conditions caused by inclement weather. In the San Bernardino National Forest, several sections of California State Route 38 were washed out by floodwaters, leading Caltrans to launch a US$9.7 million project to restore damaged sections of the road. Additionally, sections of California State Route 178 and California State Route 62 were damaged by floodwaters. Officials estimated the cost to repair roads damaged by the storm at US$40.7 million. Flooding left several roadways impassable at Death Valley National Park. In Barstow, a toddler was killed and his father was injured after their vehicle was swept away by floodwaters.
The remnants of Mario also generated severe thunderstorms across portions of Nevada and Arizona. In Clark County, strong winds downed a tree, killing a horse. In the Phoenix metropolitan area, Arizona Public Service reported that lightning activity left around 1,800 customers without power. In Gila County, five children and a dog were rescued from floodwaters.