What could Helene tell us about the hurricanes of the future

Every year, August 20thmeteorologists from Colorado State University They ring the bell to signal the start of the high season hurricanesa week-long period when high ocean temperatures tend to create frequent and destructive storms. But this year, tradition has given way to an eerie echo of silence with a flurry of activity Atlantic at a 30-year low despite projections for a historic season.

This lull finally ended this week when Hurricane Helena whipped Big Bend in Florida with violent and deadly force. Driven by exceptionally warm Caribbean watersthe Category 4 storm is one of the largest to hit the country USAand meteorologists are already warning that more cyclones are coming.

This disproportionate hurricane season illustrates the challenges meteorologists face climate change makes extreme weather less predictable and more intense. Although some scientists say that the rapid growth and historical rainfall Helen are storm symptoms influenced by human-induced warming, they are still trying to understand whether this year’s unusual storm activity is an anomaly or a sign of things to come.

“Will every season be like this? “Hard to say,” he said. Phil Klotzbachmeteorologist Colorado State University. “We’ll have to keep our eyes on the sky.

Scientists have increasing evidence that major hurricanes, e.g category 3 or higherare increasingly common, and many point to climate change as the cause. But at this point, the data is inconclusive as to whether the total number of storms will increase.

In a study published in Proceedings of the National Academy of Sciences In 2020, scientists found that the number of major hurricanes increased worldwide between 1979 and 2017. Later studies found that this trend could not be easily explained by natural variability.

He Hurricane Helena It’s the eighth storm category 4 or 5 it caused the landing in USA as of 2017, the same number of Category 4 or 5 storms that hit the country in the previous 57 years. However, the late 1940s saw a similar increase in severe storms.

“Very, very warm ocean temperatures certainly play a major role in what we see“, he said James Kossinscientific advisor First Street Foundation. “There’s a lot more fuel.

All of these major storms also had another factor in common: they all experienced what is known as “rapid intensification,” or an increase in maximum wind speed of more than 56 kilometers per hour (35 mph) in less than 24 hours. Going through record Caribbean heat, Helen It has transformed from a Category 1 storm to a Category 1 storm category 4 in the space of a single day.

According to a recent study, such rapidly intensifying storms have increased dramatically since 1990.

Rising global temperatures are helping to speed up the feedback loop between water evaporation and wind speed, he said. Kerry Emanuelatmospheric scientist from HAVE which phenomenon he studied. This shortens the time frame in which hurricanes can develop and raises the limit on how bad they can get.

“It’s like stepping on the gas pedal“, he said Emmanuelespecially for storms that intensify faster.

Other scientists warn that it may be too early to tell if these big storms are definitely increasing.

“It’s a little shady,” he said. Tom Knutsonsenior scientist at National Oceanic and Atmospheric Administration. Knutson noted that when researchers look at the past century of major hurricanes that have made landfall USAno trend is apparent. “There are still some questions,” he said.

There is clearer evidence that human-caused warming has increased the destructiveness of hurricanes by intensifying their rainfall, researchers said.

Scientists have long known that air can hold twice as much moisture for every 10 degrees Celsius (18 degrees Fahrenheit) rise in temperature.

“Even if the hurricanes themselves didn’t change their structure or the speed at which they moved, there would be more rain,” he said. Emmanuel.

Even earlier Helen After landfall, its moisture was absorbed by a storm front that moved ahead of the hurricane, dropping nearly 30 centimeters (1 foot) of rain on parts of the southeast. Studies suggest that this is called a rainfall precursor and is more common in high-intensity storms because of the way strong hurricanes interact with the jet stream.

This early rain left soils saturated and filled rivers to their banks, creating conditions for catastrophic flooding Helen advanced inland. Friday late afternoon, more than 150 gauges from Florida until Virginia They were in a state of flood. For many communities in the west North Carolinawas rain that should be expected only once in 1000 years.

“The biggest impacts come from situations like this,” he said Russ Schumacherprofessor of atmospheric sciences at Colorado State University.

Schumacher said that while more studies are needed to assess the impact of climate change, “it’s not that difficult to connect the dots” between warmer oceans, more moisture in the air and heavier previous rainfall.

“A small increase in humidity can lead to a very large increase in precipitation,” he said.

Although Helen bore some of the hallmarks of a storm affected by climate change, scientists aren’t sure what one of its most distinctive features, its size, portends for future hurricanes.

About 676 kilometers (420 mi) in diameter, Helen Among the largest storms to hit USAon a par with giants like Sandy, Katrina and Andrew. Research shows that larger storms are often disproportionately destructive. But because authorities didn’t see the size of hurricanes until relatively recently, he said EmmanuelStudies are inconclusive about whether large-diameter storms will become more frequent with climate change.

That’s one of the many questions scientists now have to ponder in retrospect Helen and the season that preceded it.

As the world moves into La Niña weather, usually associated with powerful hurricanes, and “off the charts” temperatures in the Atlantic, experts predict this season will be among the worst in decades.

But after experience Beryl in July his a category 5 hurricane For the first time in history, the ocean basin experienced the longest period in more than 50 years without a single late summer cyclone.

“The season didn’t go the way we expected,” he said. Klotbach. “And we’re still trying to understand why.”

Although hurricanes are driven primarily by the heat of the oceans, it takes more than warm water to form a storm. Some of these necessary ingredients, such as air saturated with moisture, were missing from it Atlantic this summerwhich helped suppress cyclonic activity.

This year there were also exceptionally high temperatures in the upper layers of the atmosphere. The combination of warm air over a warm ocean may have had a stabilizing effect, he said. Klotzbachwhich raises the question of whether human-induced warming may have brought the atmosphere to the point where it begins to suppress storm formation.

It is too early to tell whether the hot and dry atmospheric conditions were just idiosyncrasies of this particular period or signs of a long-term change, he said. Klotzbach.

Some forecasters expect the hurricane season to warm up next month. A cluster of thunderstorms will move in an easterly direction Africaabandonment Atlantic Ocean with favorable conditions for the formation of hurricanes.

“The end-of-season storms deserve a lot of watchinghe said Klotzbachbecause they tend to form in the western part of the Atlantic basin and do not have to travel far before coming to land. Just like Helenthat formed in the Caribbean, such storms can quickly go from unnamed tropical depressions to billion-dollar disasters.

Despite this flurry of activity so late in the year, Klotzbach He said there is no conclusive evidence that climate change can shift the peak of the hurricane season or cause it to last longer. But he and his colleagues will be studying this season carefully to understand why she behaved so unexpectedly.

However, he added “It’s also important when you have a seasonal forecast model based on 40 or 50 years of historical data that you don’t throw everything out the window if the season doesn’t turn out ideal.”

For Emmanuel, Helen’s rapid intensificationand the quiet months that preceded it highlight the challenges meteorologists face as humans continue to warm the planet. Even as weather models and forecasting technology improve, the unprecedented rate of human-induced warming is causing storms to behave in new and unpredictable ways.

“That’s one of the things that scares me, if these things can escalate fasterhe said Emmanuel. “We’re going to have cases where meteorologists go to sleep with a tropical storm and wake up to a Category 5 when it’s too late to evacuate people.”

“How difficult will it be to predict the climate in the future?” he added. “I think it’s an open and important question that science hasn’t answered yet.”

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