Hurricane Hilary could dump over a year’s worth of rain on parts of the Southwest

Hurricane Hilary looms as a potential source of concern, with the potential to unleash a deluge equivalent to over a year's worth of rainfall across sections of the Southwestern United States. There is a growing worry that this hurricane will bring about a substantial amount of flooding rain to the southwestern US and parts of California. This is an unusual occurrence as the storm moves into the region on Sunday and extends into the early part of the following week. This situation has prompted the issuance of the first-ever tropical storm watch for California.

Hilary has the capability of depositing more rainfall than what an entire year typically receives in parts of three states: California, Nevada, and Arizona. As a result of this threat, certain regions of California are facing an uncommonly high risk of excessive rainfall. This top-level threat, marked as Level 4 out of 4, is the first ever declared for this specific area of Southern California.

The hurricane, known as Hilary, was a formidable Category 4 hurricane swirling around 325 miles south of Cabo San Lucas, Mexico, on a Friday afternoon. It exhibited sustained winds of 130 mph, accompanied by even stronger gusts, according to the National Hurricane Center. The storm underwent rapid intensification between Thursday and Friday, transforming from a tropical storm into a Category 4 hurricane in a mere 24-hour span. Forecasts predict that Hilary will remain as a Category 4 hurricane as it approaches the Baja California peninsula in Mexico through Saturday.

Authorities have issued alerts and advisories for hurricanes and tropical storms across Baja California, extending from the Los Angeles area down to Point Mugu in Ventura County, as Hilary's center advances towards the region throughout the weekend.

The potential impact of the storm's strongest winds across the US remains uncertain as it progresses northward over the next couple of days. Slight deviations in the hurricane's path could alter predictions regarding the most intense rain and wind patterns.

Hilary is moving at a faster pace than initially anticipated, resulting in earlier-than-expected impacts for Mexico and California compared to earlier projections. The current assessment indicates that Hilary's core is likely to approach the central portion of Baja California on Saturday night and then continue inland over southern California by Sunday night.

The National Hurricane Center also noted that regions would experience strong winds and heavy rainfall well in advance of the hurricane's center. While the likelihood of Hilary making landfall in Mexico and crossing into California is higher, if it were to make landfall in California as a tropical storm, it would mark the first such occurrence in nearly 84 years, based on data from the National Oceanic and Atmospheric Administration (NOAA).

The issuance of the first-ever tropical storm watch for certain parts of Southern California was declared on Friday morning by the National Hurricane Center. This watch extends from the California-Mexico border to the boundary between Orange County and Los Angeles County. The hurricane center stated, "The threat of significant wind impacts continues to increase for northern portions of the Baja California Peninsula and the Southwestern United States, especially in areas of mountainous terrain."

The Southwestern United States is preparing for substantial flooding, given the expected outcomes of Hurricane Hilary. Even as Hilary is projected to weaken considerably before reaching Southern California and other parts of the Southwest, the storm is anticipated to intensify heavy rainfall and heighten the risk of flooding.

The onset of heavy rainfall is forecasted to impact the Southwest starting on Saturday and persisting through the early days of the following week, with the most intense downpours anticipated for Sunday and Monday.

The potential dangers associated with the high risks of excessive rainfall cannot be overstated. These high-risk events are issued on fewer than 4% of days on average each year, but they are responsible for 83% of flood-related damages and 39% of flood-related fatalities, as indicated by research from the Weather Prediction Center. Southern sections of California and Nevada could receive between 3 to 5 inches of rainfall, with isolated areas experiencing up to 10 inches. Additionally, central areas of these states, along with western Arizona and southwest Utah, are expected to receive rainfall ranging from 1 to 3 inches.

Hilary's impact could result in "multiple years' worth of precipitation potentially falling in some of the driest regions of California," according to Daniel Swain, a climate scientist at the University of California, Los Angeles. One such location is Death Valley, California, renowned as the hottest place on Earth. Typically, Death Valley receives about 2 inches of rain over an entire year. However, moisture from Hilary has the potential to bring about enough rain to match 1 to 2 years' worth of rainfall in a single day. In Las Vegas, rainfall of 2 to 4 inches is possible, whereas the annual average is only 3.75 inches.

Extended periods of rainfall may result in saturated ground and overwhelmed waterways, exacerbating the flood threat. The Mojave National Preserve, situated along the border of California and Nevada, has been temporarily closed due to potential flooding stemming from the storm.

As the weekend approaches, flood watches have been issued across Southern California, spanning from San Diego to Los Angeles, as residents prepare for potential heavy rainfall.

The National Weather Service in Los Angeles has cautioned about the potential for notably high surf, rip currents, and coastal flooding. Local county departments have been making preparations for the impending storm over the past few days, ensuring that rescue personnel are ready to respond promptly. Sheriff Robert Luna of Los Angeles County expressed a major concern for safeguarding individuals in the homeless community. The Greater Los Angeles area is home to around 75,000 homeless individuals, with over 46,000 within city limits, according to a 2023 estimate from the Los Angeles Homeless Services Authority. Considering this, outreach efforts are underway to provide temporary housing, particularly for those who reside in parks or near waterways.

While hoping for minimal damage and no loss of life, Sheriff Luna affirmed the readiness to prepare for worst-case scenarios and provide assistance to neighboring counties if required.

Meanwhile, not to be outdone by the East Pacific, the Atlantic region is gearing up for a surge in tropical activity. Across the entire basin, from west of the Cabo Verde Islands to the Gulf of Mexico, four separate areas of concern have emerged. The most immediate concern for the United States centers on an area within the warm Gulf of Mexico where atmospheric conditions are conducive to tropical development in the upcoming week. A low-pressure area could gradually organize, strengthen, and acquire tropical characteristics over the western Gulf by the middle of the week.

In the tropical Atlantic, three separate areas of concern are apparent. One area, characterized by disorganized showers and thunderstorms west of the Cabo Verde Islands, may organize into a tropical depression over the weekend, potentially intensifying into a tropical storm. Another area of disturbed weather adjacent to the west could potentially develop into a tropical depression by early next week. A third area has a low probability of acquiring tropical characteristics near the Lesser Antilles.