Hurricanes really aren’t supposed to get stronger than Hurricane Patricia.
That’s not hyperbole. Hurricanes shouldn’t see sustained winds above 190 miles per hour in Earth’s modern-day climate. Yet on Friday morning, Patricia’s winds were measured at about 200 miles per hour.
That’s not the only exceptional aspect of the storm. The category-five tropical cyclone, now spinning off the western coast of Mexico, is expected to make landfall Friday evening. It will be the second-strongest storm to make landfall in history, after Typhoon Haiyan in the Philippines 2013.
Remarkably, it only holds that “second strongest” title because it has weakened slightly in the past few hours. On Friday morning, Patricia was the strongest storm ever measured by the U.S. National Hurricane Center, which has monitored all storms in the Atlantic and north Pacific for the past half-century.
Patricia got extremely strong, extremely fast. Late Wednesday evening, it was merely a strong tropical storm, with peak winds of 65 miles per hour. By the following morning, it had become a category-one hurricane; and by Friday morning, it had exceeded records.
How did it intensify so quickly? Falko Judt, a meteorologist at the University of Miami who studies hurricane intensity, said the intensification wasn’t entirely unexpected. It’s just that almost everything that could go the cyclone’s way, did.
The two major factors that govern hurricane intensity, Judt said, are ocean temperature and wind shear. The ocean-surface temperature was very warm under Patricia—it was measured at 31 degrees Celsius, or more than 87 degrees Fahrenheit—which provided the storm with a lot of fuel. At the same time, wind shear was very low, which meant that wind was blowing in the same direction across multiple levels of atmosphere and there was little frictional drag on the storm.
Judt said that these two factors were aided further by very high humidity locally.
“It’s not totally unexpected to me that it intensified so quickly,” he told me. “Everything looked toward it becoming a strong hurricane. It’s just incredible how strong it got.”
What drove that strength?
Judt said that he thought El Niño played a large role. El Niño is a Pacific Ocean-spanning climate phenomenon, in which the eastern part of the ocean, near the equator, becomes warmer than usual. The central and western Pacific in turn become cooler. The effects of the climatological phenomenon are felt across the globe, which causes droughts in Australia and Ethiopia and deluges in California.
“The largest signal of El Niño is around the equator, so it tapers off at higher and lower latitudes. But Mexico is still close enough that it feels the effects,” he said.“It’s always hard to attribute one single storm to a larger phenomenon like El Niño, but it most likely did play a role.”
(Did climate change also affect the storm? Meteorologists are still debating how much global warming drove this year’s especially strong El Niño. Over at Slate, the meteorologist Eric Holthaus discusses how climate change has shaped Patricia in particular.)
Some forecasters have proposed that, to measure the planet’s increasingly strong storms, more categories should be tacked on to the end of the Saffir-Simpson hurricane-wind scale is used to measure hurricane intensity. Right now, that scale only counts to five, which equates to wind speeds over 155 miles per hour. On an expanded scale, Hurricane Patricia might qualify as a seven:
Recall suggestion for addition of Category 6 to Saffir Simpson scale? If extrapolated further, Hurricane #Patricia would be Category 7.— Ryan Maue (@RyanMaue) October 23, 2015
Judt, however, wasn’t as sure that an expanded scale was needed. Hurricane categories don’t need to measure beyond 150 miles per hour, he said, because winds at that speed cause the maximum level of destruction possible.
“I’m reluctant to change categories because categories are based on wind destruction,” he said. “Everything is destroyed in a Category Five, so everything of course will be destroyed in a Category Six, too. You can’t really assess how bad [a storm] was because everything is destroyed anyway, as bad as that sounds.”
He did note, though, that the hurricane seemed to meet or even exceed its maximum potential intensity. That’s a way of predicting cyclone intensity developed in the late 1990s by the climatologists Marja Bister and Kerry Emanuel.
Emanuel, now a professor at the Massachusetts Institute of Technology, told me Friday that his maps had correctly predicted the hurricane’s intensity: They had predicted winds as strong as 207 miles per hour, and those at 200 miles per hour had been recorded. But it was rare, he said, that a storm actually achieves its potential.
“Very few storms make it right to their speed limit,” he said. “This hurricane happened to develop in a place where its unusually strong.”
Judt echoed that statement. “Globally, at the moment, storms couldn’t get any stronger than that anywhere in the planet. Patricia found the sweet spot,” he said.
And Emanuel also added that it was possible for a tropical cyclone to have winds stronger than 200 miles per hour—but not with ocean temperatures like those in the Pacific. “In a different climate, or in a different place and time, it could just go as well with a higher number,” he said.