Hurricane Polo was closing in on Mexico's Baja California Sur on Monday as a major Category 3 storm, packing sustained winds near 115 mph and threatening the kind of flooding rescue crews spend days recovering from.

As of Monday morning, Polo was about 85 miles west-southwest of Cabo San Lazaro, according to the National Hurricane Center's advisory, and forecasters expected landfall in the state Monday afternoon, between roughly 4 and 6 p.m. local time, with some weakening to a Category 1 storm by the time it comes ashore.

Flood Threat Tops the Danger List

Wind isn't the main worry. The National Hurricane Center and NBC News' storm coverage both flagged rainfall as the storm's most dangerous feature, with 6 to 12 inches expected across Baja California Sur through Tuesday — enough to trigger life-threatening flash flooding and mudslides, particularly in steep terrain. Storm surge is expected to add significant coastal flooding in areas facing onshore winds, with large, destructive waves battering the coastline.

ACCESS TO BEACHES HAS BEEN CUT OFF AND MARITIME ACTIVITY SUSPENDED IN HIGH-RISK AREAS

Evacuations Already Underway

Baja California state authorities opened temporary shelters in five municipalities ahead of landfall. By early Monday, 78 people had already been evacuated as a precaution to a shelter in Ciudad Constitución, according to local reporting on the evacuations. The U.S. Embassy in Mexico also issued a weather alert covering the Baja Peninsula and neighboring Sonora state.

What's Next

Forecasters say Polo's moisture will push north after landfall, raising the risk of major flash flooding across parts of the southwestern United States later this week even as the storm itself weakens over Mexico. Baja California officials are urging residents in flood-prone and mountainous areas to follow evacuation orders through Tuesday as the rain bands move through.