Photograph by CIRA, NOAA
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A satellite for the National Oceanic and Atmospheric Administration captured this image of Hurricane Maria on September 18, 2017.

Photograph by CIRA, NOAA

Why a Quiet Hurricane Season Isn't Necessarily a Good Thing

A warming Arctic may cause storms to track farther west, increasing odds of landfall.

Forecasters at Colorado State University say the approaching peak of the 2018 hurricane season will be relatively quiet in the Atlantic Basin. But a report released Wednesday by the National Oceanic and Atmospheric Administration pointed out a troubling trend that could have implications for future hurricane forecasting: Warming in the Arctic could drive future Atlantic hurricane tracks farther west and thus make a U.S. landfall more likely.

The CSU forecasters, headed by meteorologist Phil Klotzbach, think cooler waters and drier air in the Atlantic Basin—which includes the Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea—along with the presence of upper-level winds known as wind shear will make it more difficult for storms to form.

Hurricanes draw their power from warm ocean waters, and warm, moist air helps sustain them. The storms that spawn hurricanes are less likely to intensify when they are deprived of fuel and face hostile atmospheric conditions, thus suggesting the 2018 season is expected to be relatively quiet.

Four named storms have formed since the hurricane season began June 1. The season ends November 30.

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CSU’s forecasters predict that nine more named tropical storms with winds exceeding 39 miles per hour will form in the Atlantic Basin. Three of those storms are likely to intensify into hurricanes with winds of at least 74 miles per hour. And one of those storms probably will become a major hurricane with winds exceeding 110 miles per hour.

The forecast is welcome news for U.S. coastal residents, who endured three devastating hurricanes during the peak of last summer’s hurricane season. Hurricane Harvey inundated Houston and the Gulf Coast on August 25, 2017. Hurricane Irma blasted across the Caribbean, dealt a devastating blow to the Florida Keys, and made a final landfall near Naples, Florida on September 10. Ten days later, Hurricane Maria pummeled Puerto Rico, causing one of the worst natural disasters in the island’s history.

The notation about the jet stream’s possible influence on hurricanes was included in NOAA’s 28 annual report on the state of the climate. The report noted that warming in the Arctic is likely affecting the jet stream—a narrow, meandering current of air several miles above the Earth’s surface that flows from West to East and often influences weather patterns around the globe.

The jet stream’s path can fluctuate, from a straight line to a wavy line, depending on warming in the Arctic. The formation of the stream can be a major factor in whether a hurricane intensifies or diminishes. It also can play a significant role in steering a storm toward or away from land.

When the jet stream becomes wavy, unusual weather events become more likely. Many scientists think Hurricane Sandy’s odd, due-west track to the coast of New Jersey in October 2012 was caused by a wavy jet stream that was in place at that time.

The wavy configuration can sometimes push Atlantic hurricanes’ tracks farther to the West, says NOAA oceanographer James Overland, and that could increase the chances that the storms might make landfall instead of curving harmlessly out to sea.

“It makes [landfall] more likely,” he said. But the theory of a meandering jet stream affecting hurricane tracks is a controversial one among scientists. The shift to a prolonged wavy configuration could come about when there is less ice than usual in Alaska.

The NOAA climate report, compiled by hundreds of scientists around the globe, is “an annual physical for our Earth,” according to Jeff Rosenfeld, editor-in-chief of the Bulletin of the American Meteorological Society. Rosenfeld said the annual report establishes baselines—such as temperatures, atmospheric conditions, rainfall, and other measurements—that allow scientists to detect changes in climate patterns.

The report notes that the Arctic continues a trend of warming at a much faster rate than the rest of the planet. And that the warming has manifested itself in some troubling trends, including a more dramatic loss of sea ice than any seen in 1,450 years, the a strangely late autumn freeze of ice in the Pacific Arctic, and one of the smallest areas of winter sea ice. Overland said it’s too early to tell whether Arctic conditions will have any influence on this year’s hurricane season.

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