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Home SCIENCE How hurricane season went from quiet to a 'powder keg'

How hurricane season went from quiet to a ‘powder keg’

Hurricane activity in the Atlantic Ocean usually begins to increase in earnest in mid-August. But at that time this year, a storm was not in sight anywhere in that vast expanse of ocean. Those quiet weeks capped a nearly two-month hiatus that had forecasters scratching their heads after initial predictions of a peak season. “He was really, really dead. We had no storms in August, which was the first time since 1997,” when a very strong El Niño cut off hurricane activity, says Phil Klotzbach, a hurricane researcher at Colorado State University who issues a seasonal forecast.

But in late September, it seemed like a switch was suddenly flipped. Four named storms formed in nine days, and two of them, Fiona and Ian, became destructive hurricanes. The 2022 hurricane season’s 180-degree turn provides an object lesson in the competing influences that can keep Atlantic storm formation at bay or turn the region into what Klotzbach calls a “powder keg.”

Prior to the official start of the current season on June 1, several forecast groups, including Klotzbach’s, predicted more storm activity than the average season (although not as successful as occurred in 2020, which revised its available hurricane names and in a backup). list of greek letters). Two large-scale patterns favored storm formation: abundant warm ocean water in the Atlantic Ocean and a La Niña event in the Pacific. During La Niña, warm waters in the tropical Pacific move westward, changing circulation patterns in the upper atmosphere. This has a ripple effect throughout the world. In the Atlantic, it means a more unstable atmosphere and less vertical wind shear (in which winds blow at different speeds and directions at different heights in the atmosphere), factors that favor the convection that drives a hurricane.

One storm formed in early June, and two more briefly developed in early July. Everything was calm then until Tropical Storm Danielle formed on September 1. The long period of inactivity stemmed from short-term factors that, for a time, overwhelmed the most favorable conditions. In particular, dry air flowing into the tropics from the northernmost latitudes and the Sahara desert deprived low-pressure systems, technically called “tropical waves,” that move off the west coast of Africa and become the seeds of many tropical storms. “You would have waves and some activity over the central Atlantic, healthy-looking things coming out of Africa, and they just wouldn’t make it. It would be right after ‘No, there’s nothing to look at here’ time,” says Brian McNoldy, a hurricane researcher at the University of Miami’s Rosenstiel School of Earth, Atmospheric and Marine Sciences.

That dry air – and, in the case of the Sahara, dust – is often present early in the season, but there seems to be more of it this year. “In this particular season, it looks like the Saharan air may have been pushed further south than average because of all these ripples” in the jet stream, the river of air from west to east in the atmosphere, Kim says. Wood, a tropical meteorologist at Mississippi State University. Saharan dust can reduce activity because it absorbs solar energy, heating higher portions of the atmosphere and making them more stable and therefore less conductive to storms, she says.

Those third conditions lasted longer through August of this year than they normally would. But by the end of the month, they were receding and La Niña influences and plenty of warm ocean water were beginning to take over. “There’s a lot of untapped rocket fuel,” Klotzbach says of waters that have spent all summer soaking up the sun’s rays. Like Danielle, Tropical Storm Earl formed in early September, and both soon strengthened into hurricanes. And then, after a few more days of quiet after those storms weakened, Fiona formed and ushered in a flurry of activity.

Fiona flooded Puerto Rico and again knocked out power to the island before finally crashing into Atlantic Canada, where it destroyed homes and left more than 500,000 customers without power. After Fiona came Gaston, closely followed by Hermione and then Ian, which quickly intensified into a major hurricane and hit Florida’s Gulf Coast on Wednesday.

September is usually the peak of hurricane season, so it’s no surprise that this activity is taking off now. But it remains to be seen whether the season will ultimately live up to forecasts of above-average activity. “It’s just climatologically we’re running out of time as we’re at the peak of the season and entering the period when activity tends to slow down,” says Wood. “We have seen past seasons, unfortunately, like 2020, where there was a lot of activity in October and November. That doesn’t mean we’re going to see that here. But it’s within the realm of possibility because the water is so warm, because the waves continue to come out of Africa.”

A slow season followed by an onslaught of storms has happened before. For example, “1961 was the only other year that didn’t have named storms in August, and it ended up being a hyperactive season,” says Klotzbach. That “September was crazy. And then October and November were very busy.”

That possibility is particularly concerning for Florida. “On average, historically, the busiest month for hurricanes in South Florida is October,” says McNoldy. “Just because it’s been silent doesn’t mean it’s over.”

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