It may very well be the strongest hurricane, for wind speeds, that human beings have ever been able to measure.
In October of last year, Hurricane Patricia spun up south of Mexico and briefly attained a wind speed intensity of 185 knots, or 213 miles per hour, on Oc. 23, based on an analysis by the U.S. National Hurricane Center. As I wrote earlier this year, there is one hurricane in the record books (a typhoon, actually) that was also claimed to have had winds of 185 knots, but that was back in the 1960s when researchers are no longer fully confident in the way wind speeds were estimated.
Patricia was therefore, for wind speeds, vastly stronger than Hurricane Matthew, also a Category 5 storm — and we saw how much damage it was capable of. Yet Matthew’s strongest winds were only estimated at 140 knots, or 161 miles per hour, in the Caribbean. Patricia is really the kind of storm that makes you think we need a Category 6.
So what created a storm like Patricia — and could there be more of them in our future?
In a new study in Geophysical Research Letters, oceanographers Gregory Foltz of the National Oceanic and Atmospheric Administration and Karthik Balaguru of the Pacific Northwest National Laboratory studied the oceanic conditions last year that triggered Patricia. Sure enough, due to the powerful El Niño event that had long been in the works and finally fully developed last year, ocean surface temperatures were much hotter than normal along the storm’s path — 1.5 degrees hotter even than they were during the strong El Niño event in 1997.
But that’s just the beginning. What mattered was not only how hot the waters were at the surface, the research finds, but the depth to which they stayed hot. You see, strong hurricanes kick up enormous waves and therefore stir the ocean greatly — bringing up cooler water from below. That cooler water can then tamp down on the storm’s intensity.
But that didn’t happen as much with Patricia. The warm water layer was very thick at the surface and the surface elevation of the ocean itself was much higher than usual, due to all the warm water that had piled up in the Eastern Pacific as a consequence of El Niño. The beginning of the so-called “thermocline,” the ocean layer between the warm surface and the cooler depths, was also considerably deeper than usual, the study finds, being weighed down by all the extra water piled up in the region.
“More than just the single large El Niño event of 2015 and 2016, it was really this long period of El Niño type conditions in the central Pacific, extending back to 2014, that tended to produce record deep thermocline anomalies in the Patricia region,” said Foltz.
“You have this really record warm sea surface temperatures, and record deep pool of warm water in the northeastern tropical Pacific.”
And still, that’s not all. The study also highlights an intriguing factor you don’t hear about much in hurricane research — the sea water in the area was fresher than usual. That’s because this was near where both the Rio Grande de Santiago and the Balsas River empty into the ocean.
Fresh water is lighter than salty water, and so this meant the column of ocean water was more “stratified” — unlikely to mix. That, too, prevented the storm from stirring up cooler waters from below.
“What this would do is it provides stability for the upper ocean, so it tends to reduce the mixing, reducing the cooling due to mixing in the upper ocean,” Foltz said.
All of this together meant the “potential intensity” the storm could achieve was simply off the charts, the study reports.
Two outside scientists contacted by the Post praised the study, but one also added that it may not be the full story.
“The fresh water anomaly (low salinity implying greater stratification) is a relatively new idea that is starting to get some traction in the research community,” said James Elsner, a researcher at Florida State University who commented on the study for the Post, by email.
“Along these lines I would argue that perhaps Matthew’s anomalous (severely under-predicted) intensification last week near the coast of South America was due to a tendency for that region to have low salinity” because of its proximity to the Orinoco and Amazon rivers, Elsner added.
“The circumstances surrounding Patricia were unusual, to say the least,” added MIT hurricane researcher Kerry Emanuel. “I agree with the authors of the study you are writing about that the unusual El Niño of 2015 played a role. But reduction of ocean mixing by extra salinity stratification, and higher than normal [sea surface temperatures] do not explain the whole problem.”
Emanuel said in his models, only when you also dial down an atmospheric parameter called “vertical wind shear” as well do you get a hurricane close to as strong as Patricia. Vertical wind shear refers to a situation in which winds in the upper and lower atmosphere blow in different directions, which can lead to the structure of a hurricane being blown apart.
The current study did not focus on the atmospheric conditions driving Patricia, noting that those would also have to be examined in the future.
“For this situation, it was record warm surface temperatures in the ocean, and a record deep pool of warm water,” said Foltz. “So it was just a really powerful combination of the two.”