Hilary Is Now a Category 4 Hurricane

Hurricane Hilary, a large and powerful Category 4 storm, was on Friday morning barreling toward the Baja California Peninsula and the Southwestern United States, where it may cause “significant and rare impacts,” meteorologists said.

The system, the eighth named storm of the Eastern Pacific hurricane season this year, had sustained winds near 145 miles per hour, according to the National Hurricane Center. Tropical disturbances that have sustained winds of 39 m.p.h. earn a name. Once winds reach 74 m.p.h., a storm becomes a hurricane, and, at 111 m.p.h., it becomes a major hurricane.

Hilary formed as a tropical storm off the coast of Manzanillo, Mexico, on Wednesday and began moving west-northwest toward Baja California as it strengthened. While the storm’s intensity was expected to fluctuate throughout Friday, it will weaken but remain a hurricane as it approaches the west coast of the Baja California peninsula on Saturday. Hilary will then likely become a tropical storm by Sunday before reaching Southern California.

Hilary’s exact landfall likely will not make much of a difference when it comes to the expected hazards in the region, meteorologists said.

Hilary will dump up to six inches of rain, with isolated amounts up to 10 inches, across portions of the Baja California Peninsula through Sunday night, with the possibility of flash flooding. Portions of Southern California and Southern Nevada will see similar rainfall totals through Wednesday, which could lead to “significant and rare impacts,” forecasters said. A flood watch was issued for Los Angeles and Ventura Counties, including Catalina Island.

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Mexico’s government issued a hurricane watch for the Baja California peninsula’s west coast north of Punta Abreojos to San Jose de Las Palmas.

A tropical storm warning was also issued for multiple regions of the peninsula.

The Eastern Pacific hurricane season has been active this summer, but most of these recent storms have tracked west toward Hawaii, including Hurricane Dora, which helped enhance extreme winds that led to the devastating wildfires on Maui.

It is “exceedingly rare” for a tropical storm to come off the ocean and make landfall in California, Ms. Sullivan said. However, storms have come close or weakened before coming ashore, still causing flooding and dangerous winds, like Kay, a post-tropical cyclone, last year. Sometimes storms even move across the state from Mexico; in 1997, Hurricane Nora made landfall in Baja California before moving inland and reaching Arizona as a tropical storm.

Hurricane season in the Eastern Pacific began on May 15, two weeks before the Atlantic season started. The seasons run until Nov. 30.

Complicating things in the Pacific this year is the development of El Niño, the intermittent, large-scale weather pattern that can have wide-ranging effects on weather around the world.

An average Eastern Pacific hurricane season has 15 named storms, eight hurricanes and four major hurricanes. The Central Pacific typically has four or five named storms that develop or move across the basin annually.

There is solid consensus among scientists that hurricanes are becoming more powerful because of climate change. Although there might not be more named storms overall, the likelihood of major hurricanes is increasing.

Climate change is also affecting the amount of rain that storms can produce. In a warming world, the air can hold more moisture, which means a named storm can hold and produce more rainfall, as Hurricane Harvey did in Texas in 2017, when some areas received more than 40 inches of rain in less than 48 hours.

Researchers have also found that storms have slowed down over the past few decades.

When a storm slows down over water, it increases the amount of moisture it can absorb. When the storm slows over land, it increases the amount of rain that falls over a single location, as with Hurricane Dorian in 2019, which slowed to a crawl over the northwestern Bahamas, resulting in 22.84 inches of rain at Hope Town over the storm’s duration.

These are just a few ways that climate change is most likely affecting these storms. Research shows there may be other impacts as well, including storm surge, rapid intensification and a broader reach of tropical systems.

Derrick Bryson Taylor, Jesus Jiménez, Orlando Mayorquin and Mike Ives contributed reporting.