People loot a grocery store after Hurricane Otis ripped through Acapulco, Mexico on Wednesday. Marco Ugarte/Associated Press
Off-the-charts warmth in the world’s oceans, so widespread and so far beyond anything ever observed, has stunned climate scientists and meteorologists for months. It set the stage for deadly floods and put Earth on track for a record-warm year.
Hurricane Otis stunned scientists anew. It intensified more quickly than any tropical cyclone ever observed in the eastern Pacific as it passed through 88-degree surface waters. The 165 mph winds it whipped into Acapulco were stronger than anything Mexico’s west coast is known to have endured from a tropical cyclone.
Again, a surge of ocean warmth likely provided extra fuel for a storm that probably would have hit anyway, but might not have transformed so dramatically – and so quickly that it gave communities little time to prepare.
“It was a bit of an extra boost,” said Colorado State University hurricane researcher Philip Klotzbach. “When you have waters that are this hot, it does load the dice for rapid intensification.”
Specifically, warm waters well beneath the surface of Otis’s path may have cleared the way for its development, scientists added. Cooler water at depths of 150 feet often inhibits tropical cyclones, as they churn it to the surface.
But ahead of Otis, “It wasn’t just warm at the surface,” said Karthik Balaguru, a climate and data scientist at the Pacific Northwest National Laboratory. “You had high ocean heat content. Those are definitely favorable conditions for rapid intensification.”
Meteorologists define rapid intensification as a 35 mph increase in a tropical cyclone’s maximum sustained winds within 24 hours. Compared to a string of storms that rapidly intensified before striking the United States in recent years, Otis was almost in another category – its wind speeds increased by 110 mph within 24 hours.
That intensification occurred as Otis moved northward toward southern Mexico in waters with surface temperatures around 88 degrees.
That is only slightly above normal in that part of the eastern Pacific, while the development of a strong El Niño climate pattern means surface waters farther south, along the equator, are more anomalously warm. But it is still “super hot,” Klotzbach said, and plenty warm to fuel rapid intensification.
A growing body of research has linked warming oceans with an increasing likelihood of rapid intensification. A study published in 2017 modeled that rapid intensification would become more frequent and severe as the planet warms.
More recent research suggests that is indeed happening, at least with the most extreme storms.
A 2018 study found that, among storms that strengthened most quickly, their rates of intensification increased by about 4 mph per decade from 1986 to 2015. Research published last year found that “extreme rapid intensification” of tropical cyclones is occurring more frequently. Researchers looked at storms that increased by 50 knots, or 57 mph, within a 24-hour period.
And in a study published last week, researchers said they found intensification has become more likely and is occurring more rapidly in the Atlantic basin.
The lead author of the most recent findings said Wednesday that while they do not apply directly to Otis and the Pacific basin, it is clear that warmer waters are conducive to faster-forming and faster-intensifying storms anywhere. In a hotter world, such overnight storm transformations are exactly what scientists have learned will be possible, said Andra Garner, an assistant professor at Rowan University in New Jersey.
“Actually seeing it happen like we did with Otis is a different thing,” Garner said. “It’s still a bit mind-blowing, I think.”
Exactly how the planet’s record warmth may have contributed to Otis’s rapid development will take months if not years to untangle, said Kerry Emanuel, professor emeritus at the Massachusetts Institute of Technology. It’s possible to record global heat in July, August, and September helped contribute to warmth deep into the water column, he said.
In that part of the Pacific, a layer of relatively fresh water close to the surface acts as a cap on top of the water that is saltier and typically cooler below. It could be that the surface waters were holding that summer warmth in place in Otis’s path, Emanuel said. But he added that he could not be sure until more data and analysis become available.
“You might find waters 40 to 50 meters down warmer than they would have been had we not had this hot summer,” he said.
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