Superstorm steering winds look less likely in future

Dan Vergano | USA TODAY

The winds that steered Superstorm Sandy straight into the East Coast look less likely to return in the future, suggests a climate forecast out Monday.

The largest Atlantic hurricane ever recorded, Sandy smashed ashore near Atlantic City, N.J., on Oct. 29. As Jersey Shore boardwalks collapsed and New York City subway tunnels flooded, 117 people died, most often from drowning, in the $65 billion U.S. disaster.

Sandy had reached major hurricane strength near Cuba in October, before it headed north. Along with its 1,100 mile-wide width, one thing that made Sandy so unusual was the storm's track, marked by a sharp, sudden westward swerve into the East Coast. Most hurricanes instead skirt the coast on a northeasterly heading, often spinning out to sea once they reach Mid-Atlantic latitudes. The role that global warming played in the disaster became part of the debate in the aftermath of the storm, with Bloomberg BusinessWeek magazine blaring, "It's the Global Warming, Stupid," on its cover immediately afterward.

"A lot of speculation after Sandy was that its steering winds were some sort of 'new normal' caused by a warming climate," says climate scientist Elizabeth Barnes of Colorado State University in Fort Collins, Colo., lead author of the new study in Proceedings of the National Academy of Sciences. The research seeks to answer part of that question by looking into whether Sandy-like steering winds look more or less likely by 2100. "We wanted to test that idea, and what we have found is that the steering winds actually look less frequent in the next century," Barnes says.

Previous estimates suggest that Sandy's westerly lurch into the New Jersey coast was a 1-in-700 year occurrence. It was driven by east-moving jet stream winds that were bottled up by two "blocking" weather patterns over the Atlantic Ocean. With the jet stream pushing Sandy out to sea blocked, westward-headed winds at lower altitudes essentially shoved Sandy ashore.

In the new study, Barnes and colleagues looked closely at the future of the Mid-Atlantic, examining the likelihood of Sandy's steering weather reoccurring by 2100. Overall, the models showed the eastward-moving jet stream strengthening in the Mid-Atlantic, and the weather-blocking patterns becoming less frequent in at least 17 out of 22 forecasts of the future. All of that means more hurricanes headed out to sea, not into the coast. Concludes the study: "Future atmospheric conditions are less likely than at present to propel storms westward into the coast."

"My interpretation is that Sandy was a rare event, and this looks like a reasonable approach to say some of the mixture of conditions that led to it look less likely in the century ahead," says climate model expert Tom Knutson of the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., who was not part of the study. Still, that doesn't mean a Sandy-like storm won't happen again, he cautions, noting the study is talking about the weather over a century's time. "Just because something has 1-in-700 odds doesn't mean you are safe for the next 700 years."

And regardless of the steering winds, Barnes adds, the study says nothing about whether hurricanes will become more or less frequent due to global warming. "That's another piece of the puzzle," she says. While most climate projections see fewer big Atlantic hurricanes resulting from global warming, recent studies by researchers such as MIT's Kerry Emanuel have suggested it might trigger more. The two things could then balance out; more hurricanes might see fewer strong westward-aimed winds on the East Coast in decades ahead, leaving the odds of another Sandy-like storm even. "All we can say now is that the atmospheric conditions that steered Sandy ashore look less likely to be frequent in the future," Barnes concludes.