Hurricane Hilary, the eighth named storm of this year’s Eastern Pacific hurricane season, is expected to rapidly intensify and could potentially bring “significant impacts” to Mexico and the Southwestern United States this weekend.

As of Thursday morning, the storm had sustained winds of 75 miles per hour, with higher gusts, 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 470 miles off the coast of Manzanillo, Mexico on Wednesday and was moving west-northwest toward Baja California. Hilary was expected to intensify on Thursday and become a major hurricane by nightfall or early Friday, meteorologists said.

A tropical storm watch was in effect for Baja California Sur, Mexico from Cabo San Lazaro southward and from San Evaristo southward.

Hilary will bring up to six inches of rain, with isolated higher amounts, across portions of the Baja California Peninsula through Monday morning, with the possibility of flash flooding, meteorologists said on Thursday. Torrential rain was also expected to hit the Southwestern United States from Friday through the start of next week. Waves generated by the storm could also form life-threatening surf and rip current conditions.

The Eastern Pacific hurricane season has been very active over the past few weeks, 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.

Whether a storm forms in the Atlantic or the Pacific, it generally moves west, meaning Atlantic storms pose a greater threat to North America. If a storm forms close to land in the Pacific, it can bring damaging winds and rain before pushing out to sea.

However, an air mass can sometimes block a storm, driving it north or northeast toward the Baja California peninsula and the west coast of Mexico. Occasionally, a storm can move farther north, as with post-tropical cyclone Kay last year, bringing damaging wind and intense rain to Southern California. Sometimes storms even move across the state; 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. Both seasons run until Nov. 30.

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

In the Pacific, an El Niño reduces wind shear, a term that refers to changes in wind speed and direction. That instability normally helps prevent the formation of storms, so a reduction in wind shear increases the chances for storms. (In the Atlantic, El Niño has the opposite effect, increasing wind shear and thus reducing the chances for storm formation.)

Hawaii is in the central Pacific but is occasionally affected by storms that form to the east. It is unusual, however, for a named storm to make landfall in Hawaii, given that the state’s land area is small and divided among several islands. The last hurricane to make landfall in Hawaii was Iniki, in 1992. In 2020, Hurricane Douglas avoided a direct hit on the state but nevertheless produced damaging winds.

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 the storm 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 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 contributed reporting.

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