The tropical wave started off Africa’s west coast in early October. It took its time, perhaps two weeks, to make the 4,500-mile trek to the warm waters of the Caribbean. The turbulence it stirred didn’t catch the attention of weather watchers like Jeff Masters until Oct. 15.
The National Hurricane Center soon designated it an Invest, a low-pressure system innocuous yet worthy of investigation. Even after meteorologists elevated it to TD 18, shorthand for a tropical depression, they assumed it would fizzle.
“We expected it to lose strength after Jamaica, and it didn’t,” said Masters, founder of Ann Arbor, Mich.-based Weather Underground, a commercial weather service. “We expected Cuba to tear it apart, and it didn’t. As it headed north we expected it to decay some, as most storms do, but it didn’t.”
On Oct. 22, Sandy was officially born, troublesome beyond belief — “a freak storm, unprecedented in so many respects,” Masters said. The destroyer that came out of nowhere produced winds reaching farther than any known Atlantic hurricane. It took dozens of lives, cost billions of dollars, plunged millions into darkness and created nightmare scenarios that not even the disaster planners anticipated.
Whatever the final cost, it already has renewed debate over both the possible influence of climate change on the storm’s movement and the preparedness of states and cities to handle increasingly violent weather events.
“We see 10 to 12 named tropical storms per season on average,” said Annes Haseemkunju, an atmospheric scientist at Eqecat, a risk-management company in Oakland, Calif. “This season we already have 19 named storms, and there’s one more month to go.”
Greater frequency will force authorities to bolster the defenses of their communities, New York Gov. Andrew Cuomo said at a news conference Tuesday in Manhattan, where the city’s subway system is flooded and may take weeks to recover.
“We have a new reality when it comes to these weather patterns and we have an old infrastructure, and that is not a good combination,” Cuomo said. “We have 100-year floods every two years now.”
What made this storm so unusual was that it merged with a low-pressure system moving eastward across the continental United States that fueled its intensity while a high-pressure system over northeastern Canada blocked the storm’s path, forcing it to turn westward and strike the East Coast, said Sharan Majumdar, associate professor of meteorology and physical oceanography at the University of Miami in Florida.
“Many times when hurricanes develop, they move out to sea,” Majumdar said. “This is a once-in-a-lifetime storm in terms of all of these factors acting in concert together. It’s very, very rare.”
The storm was fueled by an unusually warm Atlantic Ocean, giving warm water supply to the storm, said Matt Rogers, a meteorologist and president of the Commodity Weather Group, a Bethesda, Md.-based energy and agriculture commodities consulting company.
“It wasn’t just a pure hurricane,” Rogers said. “It actually converted into an extra-tropical system. It’s a hybrid — part tropical and part nor’easter.”
Sandy’s path, aided by the warm water and low air pressure, defied expectations. In doing so, it prompted public discussion about the potential causes, including climate change.
Linking a single storm to climate is very difficult, though climate change itself is well understood on a global level. Earth’s average temperature has warmed about 1.3 degrees Fahrenheit since 1900, most of which is very likely due to human greenhouse gas emissions, according to the Intergovernmental Panel on Climate Change’s 2007 report.
Identifying causes of a storm as complex as Sandy, and determining whether climate change was among them, is challenging, said Randall Dole, deputy director for research at a division of the National Oceanic and Atmospheric Administration. Scientists hunt for a climate-change fingerprint by experimenting with computerized models.
“You have to reconstruct a world that might have been,” Dole said. “And to do that you need to estimate the human influence on sea-surface temperatures” and any other trends showing human influence.