Hurricane Matthew tearing up Florida’s coast in October 2016. Image: NASA/NOAA GOES Project

If you live on the East Coast, chances are you’ve spent some time preparing for one or two major hurricane events that, mercifully, wound up being pretty tame. Was the monster storm a case of too much media hype? Perhaps, but it’s also possible that you were being protected by an invisible coastal buffer zone.

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To any Star Trek fans in the room, “buffer zone” probably calls to mind that dicey region of space between the Federation and Klingon empires. But apparently, there’s a buffer zone much closer to home that protects us from hostile forces, too. That, at least, is the conclusion of a new Nature paper by James Kossin of NOAA’s National Center for Environmental Information, who found that the area of ocean surrounding the United States’ East and Gulf coasts forms a protective barrier that weakens hurricanes during periods when hurricane activity is high throughout the Atlantic basin.

If the finding holds up, it could help solve a meteorological mystery: why the US has seen relatively few landfalling hurricanes in recent years, while the Atlantic basin as a whole is in an active phase.

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So, how do non-interstellar buffer zones work? As Kossin explains, two of the most important factors governing the formation and intensification of hurricanes are sea surface temperatures and vertical wind shear, a change in wind speed or direction with altitude. Warmer waters tend to promote the growth of hurricanes, while higher wind shear puts the brakes on big cyclones, causing them to weaken or intensify more slowly.

Importantly, sea surface temperatures and vertical wind shear tend to be inversely related: when the ocean is warmer, the winds are calmer, favoring the development of lots of hurricanes. When the seas are cooler, stiffer crosswinds help to break hurricanes down.

Image: NOAA/NCEI

Since the late 1940s, Atlantic hurricane activity has risen and fallen, during warmer and cooler phases of the so-called “Atlantic multidecadal oscillation” (AMO). But when Kossin looked more closely at conditions in different parts of the Atlantic basin, he noticed something odd: In warm phases of the AMO, when more hurricanes are being stirred up in the tropics, cooler waters and stronger crosswinds prevailed off US coastlines, forming a protective barrier.

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“When conditions in the tropical Atlantic are good for hurricane intensification, they are bad for it near the coast,” Kossin told USA Today. “This is remarkably fortuitous for residents along the U.S. coast.”

As Kossin notes in his paper, the finding could help explain the recent dearth of strong landfalling hurricanes along the Eastern seaboard. Florida was in the midst of a nearly 11 year hurricane drought until Hermine made landfall as a Category 1 this past August. This is a bit odd, seeing as the Atlantic had been in a warm phase of the AMO since the early ‘90s, with the last 10 years featuring some of the most intense hurricane seasons on record.

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Conversely, during cool phases of the AMO, fewer hurricanes form in the Atlantic, but a weakened buffer zone may make it easier for cyclones to gain strength along our coastlines. During the most recent quiet period, from the 1960s through the early ‘90s, Kossin’s data shows that hurricanes were several times more likely to undergo rapid intensification near the Eastern seaboard.

Phil Klotzbach, a tropical storm expert at Colorado State University who was not involved with the study, said Kossin’s findings “make sense,” and “fit in well with the canonical AMO.”

“All in all, I think this is an interesting study,” he told Gizmodo. “Of course, I’d love to see more realizations of the AMO further back in time to confirm if these results hold.”

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What might happen to the East Coast’s buffer zone as sea surface temperatures continue to rise due to global warming is not yet clear. For now, at least, it seems we can thank the buffer zone for throwing a bit of meteorological good fortune our direction.

Of course, we shouldn’t let invisible protective barriers go to our heads. You should still take hurricane warnings very, very seriously.

[Nature]