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As oceans warm, study finds Atlantic hurricane season is starting earlier

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For years, meteorologists heralded June 1 as the historic start of Atlantic hurricane season, but a new paper reveals that tropical storms are forming more frequently before that date as the ocean warms.

The study published in Nature Communications found that there was both an earlier start date and an earlier US first landing each year. It comes as the National Oceanic and Atmospheric Administration plans to move the official start date of the season from June 1 to May 15, which would reflect sightings of the first storms and also coincide with the start of the Eastern Pacific hurricane season. .

Hurricane season has started slowly – but it’s still early

The onset date is one of many attributes of hurricanes that seem to be changing in the face of warming oceans and human-caused climate change. Powerful hurricanes are also roaming further north, and there has been an increase in instances of rapidly intensifying, bringing stronger, wetter and more destructive storms.

“It was a hot topic,” said the paper’s lead author, Ryan Truchelut, a meteorologist who founded WeatherTiger consulting firm. “There hadn’t been a peer-reviewed article on the start of hurricane season for about eight years now.”

Since 2012, Truchelut said there have been at least seven instances where the National Hurricane Center has issued tropical storm watches and warnings ahead of the official season start date. Atlantic hurricane season has historically peaked around mid-September on average, and activity typically slows by the end of November. An average season contains about 14 named storms, with seven hurricanes and three major hurricanes.

Especially since the 2010s, Truchelut said that “the preponderance of unusual and pre-season activity that the Atlantic has seen… jumps out at me.”

  • Since 1979, the first named Atlantic storm has occurred about five days earlier on average per decade.
  • The average first landfall in the United States of a named storm has tended to be earlier by about two days per decade since 1900. That equates to about three weeks since the turn of the 20th century.

What scientists looked at

The study focused on observational data, not simulations or model outputs. Using statistical methods, the group sifted through the noise in the data to draw conclusions about when storms were forming and hitting land.

It is important to note that the era of satellites — when a complete view of every nook and cranny of the Atlantic is available – did not appear until 1970. Before that, knowledge of the position and intensity of tropical cyclones came largely from reports from ships and buoy observations. Especially in the early years, this often led to possible limitations, gaps or inconsistencies in the historical record.

It is unlikely, however, that any US storms making landfall were missed, given the population density of the US and Gulf coasts. This makes the “two days per decade” figure for the first landing date more reliable.

The authors point out that warming sea surface temperatures, which may be closely linked to human activity, play a role in the lengthening of the season. In particular, they found that ocean temperatures during the spring months contribute to restart a season, excluding other factors that affect storm formation.

“The developing environment is more favorable for [storm] genesis mainly because of the sea surface temperature,” said Truchelut. “We don’t see big changes in shear, relative humidity, or upper-level temperatures.”

Truchelut said ocean warming could be linked to both human-caused warming and natural variability.

“We are not trying to attribute how much of the 0.75 degree Celsius warming observed in May since the late 1970s could be climate change relative to what is driven by natural cycles or longer-term oscillations. term,” he noted. “But there’s definitely some in the mix, both with climate change and natural cycles.”

Atlantic hurricanes are becoming more frequent and destructive, study finds

This trend is likely to continue, he said, which is reflected in modeling by the Intergovernmental Panel on Climate Change.

While the first named storm of 2022 in the Atlantic (Alex) did not form until June 5, past the official start date of the season, the previous seven years have featured early season storms:

  • Anne (2021) – a subtropical storm that formed on May 22 and briefly swirled northeast of Bermuda.
  • Arthur (2020) – a 60mph tropical storm that formed north of the northwest Bahamas on May 16 and looped in the western Atlantic while avoiding land.
  • Bertha (2020) – a 50 mph tropical storm that formed northeast of Florida on May 27 before drifting into South Carolina and bringing flash flooding and a tornado.
  • Andrea (2019) – a subtropical storm that formed several hundred miles east of Florida on May 20. A broad diffuse band of low pressure froze into an upper-level low, below which thunderstorms evolved into a subtropical storm.
  • Alberto (2018) – Alberto was a 65 mph tropical storm that formed east of the Yucatán Peninsula on May 25. It moved north dropping 14.41 inches of rain in Heriberto Duquezne, Cuba, before making landfall near Laguna Beach, Florida on the evening of May 28. A gust of 59 mph was recorded at St. George’s Island Bridge.
  • Arlene (2017) – A non-tropical storm swirled across the open ocean east of Bermuda on April 16. On the 19th, its fronts dissipated as it broke away from the surrounding environment, with enough thunderstorms forming around its center to classify it as a subtropical storm. It gave winds estimated at 50 mph but never tracked close to land.
  • Bonny (2016) – Bonnie developed north of Great Abaco, Bahamas on May 28 but gradually weakened into a tropical depression before making landfall near Isle of Palms, South Carolina6 to 10 inches of rainfall occurred and rip currents led to the drowning of a 20-year-old man on beaches in Brevard County, Florida.
  • Anne (2015) – the first storm named after the United States on record, Ana formed May 8 east of Florida before making landfall in South Carolina two days later. Roads were washed out near Myrtle Beach and Kinson, North Carolina saw 6.7 inches of rain.

The study concluded that future ocean warming could continue to advance the onset date of Atlantic storms by about half a day to a day per year.

James Kossin, a hurricane researcher with the Climate Service, who was not involved in the study, wrote in an email that this study builds on previous work linking the length of the tropical storm season of the atlantic to ocean temperatures. But he also wrote that there is no strong evidence to support further lengthening in the future.

“[T]there is no clear reason to expect the trend to continue,” he wrote. In a blog post about RealClimate last yearhe and his co-authors argued that even if the oceans warm, the atmosphere may respond in ways that counter the formation of early-season storms in decades to come.

Jason Samenow contributed to this report.