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Atlantic hurricane season is over. Here are 5 things that stood out.

Chris Corbett from Norwell walks along a breakwater in Scituate Harbor as huge wave churns behind him. The remnants of Hurricane Lee put on quite a show at high tide.John Tlumacki/Globe Staff

Atlantic hurricane season ends Thursday — and, like so many in recent years, was unusually active.

A total of 20 tropical or subtropical storms spun up, including seven hurricanes and three major hurricanes. Total activity, measured by a figured called ACE or Accumulated Cyclone Energy, was 20 percent above average.

Seven of the last eight hurricane seasons have featured above-average activity; the 2022 season was the only exception and it had near-average activity.

Perhaps one of the more surprising elements of the season was that it wound up being above average despite a burgeoning moderate to strong El Niño. El Niño begins as a warming of waters in the eastern tropical Pacific, and tends to result in sinking air over the Atlantic that inhibits storm formation. It also tends to increase wind shear, or changing winds with height, in the tropical Atlantic, which disrupts storm development.

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But record-warm waters — increased by human-caused climate change — prevailed over most of the Atlantic for large parts of the season helping to fuel storms and offset the hostile influences from El Niño.

Here, we look back at five interesting aspects of the season.


1. The first storm formed in January

The year's first storm formed months before the season even started in June and is one you probably never heard about. Why? It never got a name. The National Hurricane Center didn't declare there was a January storm until May 11.

The storm began as a nontropical low, akin to a nor'easter, over the northwest Atlantic. But a flare-up of thunderstorms occurred in a pinched-off bubble of warm air near the storm system's center. Those thunderstorms grew in intensity as they extracted energy from the warm waters of the Gulf Stream. The system shed its fronts and contained winds of 40 to 50 mph, above the threshold for classification as a subtropical storm.

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While some meteorologists argued for it to be named Arlene in January, it wasn't until after the fact that the Hurricane Center formally recognized its strength.


2. The eighth Category 5 in eight years formed

Remember Lee? The storm that seemed to never go away? It formed on Sept. 5, then underwent explosive intensification Sept. 7 and 8. Lee's peak winds leaped 80 mph in 24 hours to become a Category 5 hurricane. It is one of only six hurricanes on record to intensify that fast.

It stayed out at sea, however, before eventually reaching the Canadian Maritimes on Sept. 16 as an intense nontropical storm.

The Atlantic has seen eight Category 5 hurricanes in the past eight years.


3. Hurricane Idalia contained damaging ‘miniswirls’

Ever heard of a miniswirls? Their existence was hypothesized in 1992 following renowned physicist Ted Fujita's survey of the damage left by Category 5 Hurricane Andrew in Florida.

Miniswirls are small whirlwinds a few feet wide. They begin at the surface, much like little leave whirls in the autumn. But they get vertically stretched because strong hurricane winds just above the ground. That strengthens them. A miniswirl might have winds of 30 to 40 mph, but, when whipping around the center of a hurricane, can intensify resulting in narrow strips of severe damage.

Hurricane Idalia, which made landfall as a Category 3 in Florida's Big Bend in August, brought numerous miniswirls ashore. Until Idalia, there weren't many definitive videos of miniswirls. However, dozens swung through Perry, Fla., on Aug. 30, where scores of storm chasers had congregated.

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4. Most Atlantic land areas were lucky

Even though there were more named storms than normal this year, Idalia was one of only two hurricanes to strike land. Idalia was the strongest hurricane to strike Florida's Big Bend in 125 years, producing $2.5 billion in damages, but it struck a sparsely populated area preventing a much larger toll.

The other hurricane to make landfall - Tammy - was just a Category 1 with 85 mph winds when it struck Barbuda on Oct. 22.


5. California and Texas both got ‘H’ storms the same week

Tropical Storm Hilary, a Pacific storm, drenched the California deserts on Aug. 20. Death Valley got a year's worth of rainfall in one day - 2.22 inches. Palm Springs logged 3.18, more than two-thirds of the city's typical yearly rainfall.

Then in the Atlantic, Tropical Storm Harold made landfall two days later. It hit South Padre Island, Tex., on Aug. 22 with 50 mph winds. Corpus Christi received 5.25 inches of rain.


Next year could be extra active

The National Oceanic and Atmospheric Administration predicts that the El Niño will linger into spring. However, by the peak of next hurricane season in August and especially September, the pendulum may swing back toward La Niña. That's left many forecasters expecting an even more active season next year.

During a La Niña, reduced wind shear increases how many storms can form in the MDR, or Main Development Region. The MDR is the zone of the tropical North Atlantic between Africa and South America where some of the most dangerous, long-lived hurricanes form. Usually, during El Niño seasons, the more significant storms form closer to North and Central America in pockets of reduced high-altitude winds, rather than in the MDR. If La Niña develops, favorable environments for storms will probably cover more area.

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Moreover, La Niñas foster ascent, or rising motion, in the air over the Atlantic. That makes it easier for storms to form.

Yet another factor that could boost storm activity? Ocean temperatures. They reached record-warm levels in 2023, and it's expected that the Atlantic and Gulf of Mexico will remain unusually hot in 2024.

Putting it all together, the deck is stacked toward yet another active season. If it seems it’s been a while since coastal residents could truly catch their breath, that’s because it has. Unfortunately, 2024 doesn’t look like an opportunity to lower one’s guard.