Parts of the Southwest are bracing for the potential impact of Hurricane Hilary, which has the potential to unleash an entire year’s worth of rainfall in the region.

Growing apprehension surrounds Hurricane Hilary as it looms to release an abundant deluge of flooding rain across the southwestern US and portions of California, embarking on an unusual trajectory over the region from Sunday onwards into the following week. This rare occurrence has prompted the issuance of California’s inaugural tropical storm watch. Hilary’s potential impact is substantial, with the prospect of inundating regions in California, Nevada, and Arizona with rain exceeding a year’s worth. Consequently, certain parts of California are under an extraordinary high-risk alert for excessive rainfall – the first-ever Level 4 threat in this segment of Southern California.

Presently a formidable Category 4 hurricane, Hilary churns about 400 miles south of Cabo San Lucas, Mexico, boasting sustained winds of 145 mph and even stronger gusts, as reported by the National Hurricane Center on Friday morning. The storm underwent a remarkably swift intensification from Thursday to Friday, transforming from a tropical storm into a Category 4 hurricane within a mere 24-hour span. Hilary’s projection maintains it as a Category 4 as it approaches Mexico’s Baja California peninsula, poised to continue through Saturday.

The possibility lingers that Hilary could briefly escalate to a Category 5 hurricane for the first time this season before encountering colder waters, resulting in some loss of strength. Authorities have taken precautionary measures, issuing hurricane watches, tropical storm watches, and tropical storm warnings for Baja California and northwestern Mexico, coinciding with Hilary’s imminent approach to the region over the weekend.

As the storm advances northward over the next few days, a wide range of scenarios remains for the most potent winds in the US. Even slight deviations in Hilary’s path could alter forecasts for the most intense rainfall and wind. While Hilary is more inclined to make landfall in Mexico before traversing into California, if it does make landfall in California as a tropical storm, it would mark the first occurrence of such an event in nearly 84 years for the state, based on data from the National Oceanic and Atmospheric Administration.

The initial-ever tropical storm watch for sections of Southern California was issued on Friday morning, extending from the California/Mexico border to the boundary between Orange County and Los Angeles County. As of Thursday night, the hurricane center emphasized the escalating threat of significant wind impacts for the northern regions of the Baja California Peninsula and the Southwestern United States, particularly in mountainous terrain.

Anticipating the substantial weakening of Hilary before its arrival in Southern California and the southwestern parts of the US, the storm, regardless of its force, is poised to intensify heavy rainfall and heighten the risk of flooding. The onset of heavy rainfall is projected to affect the Southwest from Saturday onward and into the early days of the following week, with the most intense deluges anticipated on Sunday and Monday.

The significance of the elevated risks for excessive rainfall cannot be overstated. High-risk designations, which occur on fewer than 4% of days on average per year, are responsible for a staggering 83% of flood-related damage and 39% of flood-related fatalities, as indicated by research from the Weather Prediction Center.

Southern regions of California and Nevada are poised to receive between 3 to 5 inches of rain, with isolated pockets possibly experiencing up to 10 inches. Meanwhile, central sections of these states, along with western Arizona and southwest Utah, are anticipated to witness rainfall ranging from 1 to 3 inches.

Hilary’s potential impact is illustrated by the possibility that “multiple years’ worth of precipitation could potentially fall in some of the driest parts of California,” as stated by Daniel Swain, a climate scientist at the University of California, Los Angeles. Notably, this includes Death Valley, California, recognized as the hottest place on Earth, where the typical annual rainfall barely reaches 2 inches. Yet, moisture from Hilary could deliver a staggering 1 to 2 years’ worth of rainfall to Death Valley in a single day. Las Vegas could also experience 2 to 4 inches of rain, a significant departure from its average yearly rainfall of 3.75 inches.

The prolonged period of rain could lead to oversaturation of the ground and the potential for waterways to become overwhelmed, exacerbating the flood risk. In preparation for the impending deluge, flood watches for the weekend have been declared across southern California, spanning from San Diego to Los Angeles.

In tandem with these alerts, the National Weather Service in Los Angeles has cautioned about the potential for perilously high surf, rip currents, and coastal flooding.

Amidst the intense meteorological activity in the East Pacific, the Atlantic is also poised for a substantial surge in tropical activity over the next few days. Four distinct areas of concern stretch across the entire Atlantic basin, ranging from west of the Cabo Verde Islands to the Gulf of Mexico.

The Gulf of Mexico is of immediate concern to the United States due to atmospheric conditions that could foster tropical development in the upcoming week. An area of low pressure in the warm Gulf waters may gradually organize, strengthen, and acquire tropical attributes over the western Gulf by the middle of the following week.

In the tropical Atlantic, three separate areas warrant attention. One area, characterized by disorganized showers and thunderstorms west of the Cabo Verde Islands, might evolve into a tropical depression over the weekend, potentially intensifying further into a tropical storm. Another zone of unsettled weather immediately to the west also has the potential to develop into a tropical depression early next week. A third area, although with a low likelihood, could acquire tropical characteristics near the Lesser Antilles.