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At the end of May, the National Oceanic and Atmospheric Administration (NOAA) released its 2018 hurricane forecast, predicting a likely active or above active season in the Atlantic Ocean -- though certainly not on par with 2017's exceptionally stormy season.

But almost a month later, conditions in the Atlantic are showing signs that the 2018 season might be quieter than forecasters initially thought.

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Specifically, surface water temperatures in the tropical Atlantic are unusually cold. When these waters are cooler, it tends to damper the formation of powerful storms, Phil Klotzbach, a research scientist in the Department of Atmospheric Science at Colorado State University, said in an interview.

"This is very unusual," said Klotzbach.

Back in March, the cooler water temperatures were pretty similar to those a year earlier, in March 2017. But since then, tropical waters have simply failed to warm.

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"The water went from normal to the coldest since 1982," said Klotzbach. "It's the coldest water temperature at this time over the last 35 years."

This is all the more strange, he said, because globally oceans have warmed. Most of the world's accumulating heat, due to climate change, collects in Earth's absorbent waters.

"To me, it's just fascinating given how much warmer the globe is," said Klotzbach.

Of course, this is not to say a powerful, potentially destructive storm won't arise and pummel the Caribbean or the coastal U.S.

"It’s not an inactive season when the wind blows 100 mph in your backyard," Hugh Willoughby, a hurricane researcher at Florida International University, said in an interview. "It doesn’t mean you can’t have bad luck."

Hurricane forecasts are never set in stone

In late May, just before the official start of the Atlantic hurricane season on June 1, NOAA predicted just a 25 percent chance of a "below normal" season.

A calmer season may look more likely now, but forecasting the weather months in advance is always challenging, and comes with inherent uncertainties.

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"The ocean is as unpredictable as the atmosphere but on a longer timescale," said Willoughby.

NOAA's 2018 Atlantic hurricane forecast as of May 24, 2018.Credit: noaa

And NOAA took this into account, months ago.

The agency noted that although the tropical Atlantic and Caribbean waters, known as the "main hurricane development" region, had "anomalously cool" waters at the time, there was still considerable uncertainty about what would happen during August and September, the peak of the hurricane season, Jerry Bell, the lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center, explained over email.

When temperatures in the tropical waters remain cooler and don't warm, a few things can suppress hurricane activity, said Klotzbach.

For one, hurricanes "live off warm ocean water," he said, so these storms have less fuel when ocean temperatures are colder. Second, colder sea surfaces generally mean more dense air over large swathes of the ocean -- and with denser air comes more overall stability. Lastly, colder tropical waters often mean stronger trade winds blowing from the east that can "tears apart hurricanes," said Klotzbach.

Hurricanes Katia, Irma, and Jose in September 2017.Credit: Noaa

If these tropical waters don't warm up soon, conditions will be mostly locked in for a milder storm season.

"There's still some time for it to change," said Klotzbach. "But usually when you get to July things are set."

"If it's going to change, it's got to change soon," he added.

Hurricane forecasts are still quite important, despite any inherent uncertainty.

"A forecast -- if you have a realistic idea of its credibility -- is better than no forecast," said Willoughby.

These forecasts can help slow-moving ocean tugs decide if they should take other oceanic routes, for instance. But most of all, "It's good for getting people started thinking about hurricanes," said Willoughby.

NOAA measures sea surface temperatures in a variety of ways, including ocean gliders.Credit: noaa

Last season brought three major storms to the United States, causing $265 billion in damages.

In addition to cooler tropical waters, NOAA has raised the possibility of a 2018 El Niño event in the Pacific, which often brings stronger opposing winds to the Atlantic.

"That's very well understood," said Willoughby. "It kills hurricanes."

Both hurricane scientists and the public alike will see how things ultimately take shape this season -- though many won't find a quieter season too disappointing.

"I have to admit that an inactive season wouldn’t break my heart," said Willoughby.

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