Here Comes Hilary: What We Know About the Cat 4 Hurricane Steaming Toward Desert Southwest

Hurricane Hilary, upgraded Friday morning to a major Category 4 storm with sustained winds near 140 mph, continues to churn and strengthen off the western coast of Mexico as it approaches a potential landfall along the Baja peninsula this weekend.

The National Hurricane Center classifies Category 4 as a major storm with winds between 130 and 156 mph, capable of causing “catastrophic damage.” A Category 4 storm has the potential to topple trees and power poles, tear roofs off well-built homes, and cause weeks-long power outages.

Hilary is expected to weaken by Saturday, but a hurricane -- or even a tropical storm -- impacting the southwestern U.S. would be a rare weather event even for this summer that's been full of them.

“Weakening is expected to begin by Saturday, but Hilary will still be a hurricane when it approaches the west coast of the Baja California peninsula Saturday night and Sunday,” the NHC's latest advisory says. “Hilary is expected to weaken to a tropical storm by Sunday afternoon before it reaches southern California.”

The biggest concern for residents in southwestern California, Arizona, and Nevada is flash flooding. The latest forecasts call for Hilary to become a major rain event across the inland deserts and mountains. Palm Springs could see as much as 7 inches of rain in the span of 72 hours.

If Hilary makes landfall, whether along the northern Baja peninsula or southern tip of California near San Diego, it would likely be as a tropical storm or depression, but coastal flooding would still be a major concern.

“Large swells generated by Hilary will affect portions of the coast of southwestern Mexico and the Baja California peninsula over the next few days, the advisory says. “These swells are likely to cause life-threatening surf and rip current conditions."