Across much of the Atlantic Ocean, from Cuba to Texas and Florida to Newfoundland, hurricanes and tropical storms have flooded streets, taken out the power and caused serious damage to cities this year.
In the northeastern Pacific, storms have also been churning to life: So far this year, there have been 16 named storms, including six hurricanes, with more than a month remaining in the season.
The latest is Pamela, which made landfall on Mexico’s mainland on Wednesday as a hurricane.
The Pacific hurricane season begins on May 15, and like the Atlantic season, which begins on June 1, it runs through Nov. 30. But because of geography and wind patterns, among other factors, hurricanes in the Pacific tend to draw less attention than their Atlantic counterparts, even though they can still bring dangerous conditions to cities and ships.
How do the seasons compare?
Because of atmospheric conditions, when the hurricane season in one ocean is stronger, it usually means the other will have a weaker season, said Dr. Nan Walker, a professor of coastal studies at Louisiana State University.
That means this year, the northeastern Pacific could continue to have a slightly weaker season than the Atlantic, which, as of late September, has formed 20 tropical cyclones — circular storms that form over warm waters with very low air pressure at the center, and winds greater than 74 miles an hour.
On average, there are typically 15 named storms in the Pacific each season. In the Atlantic, there are 14. (Last year, there was a record 30 named storms in the Atlantic, according to the National Hurricane Center.)
Still, while the Atlantic has produced more storms than the Pacific this season, the tropical cyclones that form in both oceans “pose an identical threat to mariners and land areas,” said Dennis Feltgen, a meteorologist with the N.H.C. in Miami.
Pacific storms rarely hit land.
A majority of storm systems in both oceans track from east to west, experts said. In the Atlantic, that means many storms will most likely affect the Caribbean, Mexico and the eastern and southern coastlines of the United States. In the Pacific, however, it means “very few have any impact to land,” Mr. Feltgen said.
“They don’t really pose a threat to the U.S. West Coast,” said Dr. Haiyan Jiang, a professor of meteorology at Florida International University in Miami.
In fact, said Dr. Paul Miller, a professor of coastal meteorology at Louisiana State University, wind “typically carries them away from North America into the open ocean.”
Since the storms mainly move over the Pacific’s vast stretches of open water, they often gain strength because there is no land mass to weaken their energy, experts said.
Dr. Richard Olson, the director of extreme events research at Florida International University, said if a storm is strong enough in the Pacific, it might get some attention. But because the United States is mostly spared from those storms, they do not receive the same concern as those in the Atlantic, he added.
But the storms sometimes reach western Mexico and the West Coast.
Storms do sometimes make landfall in western Mexico, and their remnants usually bring rainfall to its northeastern regions, as well as to Texas, New Mexico and Oklahoma, said Dr. John Nielsen-Gammon, a climatologist at Texas A&M University.
“It basically cranks up the amount of rainfall that gets produced because there’s so much moisture in the air from these storms,” he said.
Although most storms move westward, deeper into the Pacific, some do turn, boomerang-like, back toward Mexico, said Dr. Hugh Willoughby, a professor at Florida International University who studies hurricane motion.
When a storm does recurve, it often loses strength because of contact with colder water from the Baja California peninsula or the California coastline.
“If you’ve ever been swimming in San Diego, you know how cold the water is,” Dr. Willoughby said. “That’s poison for hurricanes.”
The last time a hurricane struck California, according to the National Oceanic and Atmospheric Administration, was the San Diego Hurricane of 1858, which brought winds of about 75 miles per hour. The Herald Tribune reported the day after the storm that “the whole heavens seemed closing in with bank upon bank of dark, heavy, ominous-looking clouds, fleeting pretty close down to the ground, before the increasing gale.”
In 2015, Hurricane Patricia, whose winds reached the Category 4 speed of 150 m.p.h., broke the record for the strongest storm on record in the northeastern Pacific and North Atlantic basins, according to the hurricane center.
Climate change means we can expect storms ‘to be more intense.’
Researchers have suggested that climate change is causing some storms to intensify more rapidly. That includes storms in the Pacific, Dr. Willoughby said.
“There’s every reason to expect them to be more intense,” he said.
Dr. Nielsen-Gammon said he had not seen an increase in the total number of storms, but he had tracked an increase in the total number of intense storms.
A warming planet could expect stronger hurricanes over time, and more of the most powerful storms — though the overall number of storms could drop because factors like stronger wind shear could keep weaker storms from forming.
Hurricanes are also becoming wetter because there is more water vapor in the warmer atmosphere, and rising sea levels are also contributing to higher storm surges, the most destructive element of tropical cyclones.
How has the 2021 Pacific season gone?
This season has been about average in terms of the number of storms and their intensity, experts said.
But some storms have still caused damage and death in some communities across western Mexico.
In August, Tropical Storm Nora unleashed a torrent of rain and flash floods on the western coast of Mexico, and it was blamed for the death of a boy whose body was found after a hotel in Puerto Vallarta partly collapsed, according to the governor of Jalisco State.
Its remnants caused heavy rain in Arizona, Colorado and Utah, according to meteorologists.
The storm called Pamela approached the southern tip of the Baja California peninsula as a hurricane on Tuesday night, according to the N.H.C. It made landfall on west-central Mexico on Wednesday as a hurricane — making it an example of the uncommon storm that recurves toward the mainland, experts said.
What about the storms in the central and western Pacific?
The western Pacific storm season — which affects many areas, such as the Philippines, Japan and China — essentially runs year-round because the water temperatures are always warm enough to support tropical cyclones, Dr. Nielsen-Gammon said. There, tropical cyclones are called typhoons, a designation that comes down to location.
It’s uncommon for storms to form in the central Pacific, but when they do, Hawaii is often the only area affected, Dr. Jiang said. In 1992, for instance, Hurricane Iniki hit the state as a Category 4 storm, killing at least six people and destroying more than 1,400 homes. More recently, Tropical Storm Olivia made landfall in 2018.
Many other storms that do form “just stir in the middle of the ocean,” Dr. Walker said.