There are myriad lessons that have emerged from the storm, but here are four key issues deserving of special attention.

Floodwaters pour into the Hoboken PATH Station in Hoboken, N.J., near the time of high tide on Oct. 29, 2012, as Hurricane Sandy made landfall.
Credit: The Port Authority of New York and New Jersey.

First and foremost, Sandy drove home the need to rethink coastal development practices that encourage growth in vulnerable areas. Second, the storm, which was forecasted well in advance, proved the value of a robust weather and climate forecasting infrastructure at a time of budget austerity. Third, Sandy revealed a disconnect between the weather community, emergency management officials, and the public when it comes to warnings about an unusually complicated severe weather hazard.

Finally, while direct links between the storm and climate change are difficult to discern, it should be seen as ushering in a new era of consequences for coastal areas due to the combination of long-term, global warming-related sea level rise and storm surges from hurricanes, Nor’easters, and other storms.

Lesson 1: Rethink Coastal Development

Hurricane Sandy delivered a clear message that the relentless pursuit of coastal development needs to be rethought. According to the National Oceanic and Atmospheric Administration (NOAA), 39 percent of the U.S. population lives in counties directly on the shoreline, and if current population trends continue, that coastal population will grow to nearly 134 million from 122 million by 2020.

In Sandy’s wake, federal flood insurance policies that subsidize growth in vulnerable areas are being re-evaluated, as are state and local regulations that have inadvertently put people in harms’ way. One federally funded program in New York is allowing the government to buy out homeowners who have damaged property in the most prone locations, rather than encouraging them to rebuild.

But as the New York Times reported on April 26, that program is being met with mixed success, as many storm victims are choosing to rebuild rather than move.

New York Gov. Andrew Cuomo (D) has repeatedly emphasized the need to redevelop the state’s coastline in a smarter, more storm-resistant way. “We can never make up for the hardship that people went through,” he said at an April news conference, “but we can use this as a learning and an improving opportunity.”

Coastal flooding in Mantoloking, N.J., as taken from a New Jersey Air National Guard Helicopter. Credit: NJNG/Scott Anema.

Cuomo’s message, though, has not done much to change the status quo. Policy makers have not come anywhere close to settling on a broader plan to protect New York City from another damaging storm-surge event. Projects, such as building a surge barrier at the entrance to the harbor, for example, largely remain at the drawing-board stage.

“There has been much more talk than action in rethinking coastal development. Many landowners have chosen to rebuild in place, meaning they’re willing to take the risk of another Sandy,” said Michael Gerrard, a law professor who directs Columbia University’s Center for Climate Change Law.

“Few, if any, firm rules have been issued by any agency,” Gerrard said. “No announcements have been made of major changes in the siting of infrastructure. We seem to be witnessing, for the most part, a continuation of business as usual, with a twinge of anxiety and a lot of meetings.”

For the insurance industry, Hurricane Sandy was another example of the rising costs of natural disasters, and a warning of the coming consequences due to sea level rise and extreme weather events. According to the reinsurance company Swiss Re, Hurricane Sandy cost at least $70 billion in total damage, with $35 billion in insured losses.

“Hurricane Sandy was a wake-up call that our coastlines are increasingly vulnerable to storm surges from rising sea levels. Low-lying coastal areas with dense concentrations of property may no longer be suitable for building and rebuilding. Difficult decisions will need to be made,” said Cynthia McHale, who directs the insurance program at Ceres, which is a national coalition of investors and environmental organizations focused on sustainability. She said insurers are raising rates in coastal locations, while pushing for governmental action to reduce the risk of more damaging events.

“We have a choice: to either gamble on bigger long-term risks or preemptively invest to make vulnerable coastal cities more climate resilient, thereby making today’s at-risk areas more insurable,” McHale said.

Lesson 2: Invest in Weather and Climate Infrastructure

For weather forecasters, Hurricane Sandy was largely a success story, as advances in remote sensing and computer-modeling techniques enabled meteorologists to accurately predict the storm’s path nearly one week in advance. Crucially, computer models — particularly a model developed by the European Center for Medium Range Weather Forecasts — foresaw the westward turn that Sandy took after moving parallel to the East Coast. That left hook brought the storm into the Mid-Atlantic states at a perpendicular angle, which put areas along and to the north of the storm’s center — all of New Jersey north of Atlantic City as well as southeastern New England — in the area of the strongest winds and highest seas, thereby maximizing the storm surge there.

Historical tracks of tropical storms and hurricanes in the Mid-Atlantic and Northeast, with Hurricane Sandy's track indicated.
Credit: NOAA via Bob Henson, UCAR.

As researchers have since shown, Sandy’s track was likely unprecedented compared to the historical records of tropical storms and hurricanes in the region.

The storm clearly demonstrated the value of weather monitoring and forecasting technology, and the need to continue to invest in both, which has been an uphill fight on Capitol Hill, given the recent emphasis on budget cuts.

“I think Sandy helped with identifying for the public how crucial a national federal infrastructure is for these scale events,” said Marshall Shepherd, a meteorology professor at the University of Georgia and the current president of the American Meteorological Society. “Sandy was not owned by one jurisdiction and required a coordinated federal response.”

NOAA officials have repeatedly cited Sandy in their lobbying push for continued funding for the next-generation of polar-orbiting satellites, telling Congress and the public that forecasts would be far less accurate if just one satellite were to go dark.

Lesson 3: Learn from Communications Failures

While forecasters succeeded in accurately predicting the path and impacts of the storm, there were flaws in how the threat was communicated to the public. For starters, there were no hurricane watches or warnings issued north of the North Carolina coastline, since the National Hurricane Center in Miami, Fla., feared that confusion might result if they were to issue such warnings only to drop them once the storm transitioned from a purely tropical one to a “post-tropical” storm system, which it did on Oct. 29, 2012, shortly before landfall. In such a scenario, the public might wrongly think the danger had passed, NOAA officials said.

A computer model projection made on Oct. 28, for sea level pressure and winds a few thousand feet above the surface on Oct. 30, as Hurricane Sandy crosses the New Jersey coastline. Credit: Weatherbell.com.

During Sandy, the National Weather Service was operating under a set of rules — since changed — that restricted their ability to leave hurricane warnings in effect after a hurricane transitions into a post-tropical storm. According to the new guidelines, drawn up in Sandy’s wake, forecasters will have the option of continuing tropical storm and hurricane warnings after a storm makes the post-tropical transition.
 It is not clear yet to what extent the lack of hurricane warnings played in evacuation decisions, but some have speculated that it may have contributed to New York Mayor Michael Bloomberg’s decision to hold off on evacuation orders until just 24 hours in advance, which likely limited the number of evacuees.

Another communications challenge concerned the strength of the storm. Since Hurricane Sandy was a Category 1 storm on the Saffir-Simpson scale as it approached the Mid-Atlantic states, some may have dismissed it as a minor threat along the lines of Tropical Storm Irene, which hit in 2011 and caused comparatively minor damage in New Jersey and New York.

The Saffir-Simpson scale does not take into account a storm’s size or its potential storm surge, making it an incomplete indicator of a storm’s damage potential. A large Category 1 or 2 storm like Sandy can cause just as much coastal devastation as a small Category 3 storm, for example. Furthermore, sea level rise means that any storm, be it a weak or major hurricane, may be more damaging than a similar storm occurring several decades ago. Discussions are underway to try to communicate a more complete spectrum of storm threats, rather than having forecasters continue to stress the category designation alone.

One alternative to the Saffir-Simpson scale would provide some of the information that the public currently lacks — a measure of how a storm’s size may contribute to its damage potential. This metric, known as “Integrated Kinetic Energy” or IKE, takes a storm’s size as well as the strength of its winds into account. Hurricane Sandy was the largest hurricane on record, as measured by the diameter of its wind field. Because of its large size, it set a huge expanse of Atlantic Ocean water into motion, ultimately building seas to unprecedented heights at the entrance to New York Harbor .

The Integrated Kinetic Energy calculation was more than 300 terajoules for Hurricane Sandy, which was the largest IKE measurement for any hurricane between 1990 and 2006, which makes it larger than the IKE figure for Hurricane Katrina, which struck the Gulf Coast in 2005.

“If the public was aware that this number was so high, which is an indication of the large potential for damage from storm surge and waves, some of them might have been able to make better life- and property-saving decisions,” said  Vasu Misra, an associate professor of meteorology at Florida State University, in a press release.

Lesson 4: Get Used to the Age of Consequences

For some, Hurricane Sandy became the new poster event of global warming. While attributing certain characteristics of the storm — such as its record size — to global warming is difficult, if not impossible at this time, it is clear that global warming exacerbated the damage by helping to boost sea levels in the affected areas.

Factors that contributed to the top 10 high-water events measured at New York’s Battery Park from 1900 to present. The water height for each event is shown against the benchmark of mean lower low water averaged between 1983 and 2001. Sea level rise (about a foot since 1900) is depicted as a component of storm surge. Although Sandy’s surge peaked close to high tide, other events had even higher tide levels.
Credit: Carlye Calvin and Bob Henson, UCAR; data courtesy Chris Zervas, NOAA National Ocean Service.

In New York City, for example, sea level has risen by about a foot during the past century, due to both sea level rise and local land subsidence. This meant that the record surge rode atop a higher baseline water level than it would have had the storm struck a century ago. And with scientists predicting up to 3 feet of sea level rise by 2100, coastal cities around the world will face even greater threats.

The coastal flooding from Sandy’s storm surge played out nearly exactly as scientists had previously warned in a series of reports commissioned by state and city governments. All of the subway tunnels connecting Brooklyn and Queens with Manhattan were flooded, as was the tunnel linking Hoboken, N.J., and Manhattan. Air travel was paralyzed, too, as all three major New York area airports experienced coastal flooding and were closed for days, along with Teterboro Airport in northern New Jersey, which is the busiest general aviation airport in the country.

Hurricane Sandy fit into the extreme weather theme of 2012. The storm spun its way ashore in the midst of the hottest year on record in the U.S., when sea surface temperatures off the East Coast were also running well above average, and at the same time that one of the worst droughts since the Dust Bowl era of the 1930s was turning the normally productive soil of the Midwest into dust.

One of the more intriguing areas of research that could yield insights into the way climate change contributes to extreme events concerns the jet stream — the high-altitude ribbon of fast-moving air that steers weather systems around the world — and the rapidly warming Arctic, where sea ice plummeted to a record low in September 2012.

The shape of the jet stream that gave rise to Sandy was viewed with awe by some meteorologists, and suspicion by others.

As the storm began moving north-northeast away from the Bahamas, a massive area of High pressure aloft set up shop over northeastern Canada and Greenland. This high, fittingly known as a “blocking high,” prevented Sandy from moving out to sea. At the same time, a deep dip in the jet stream began to dig southward into the Midwest, and the airflow around these two features scooped up Sandy and turned it northwestward, toward land.

Some studies have tied an increase in the “blocking highs” near Greenland, as well as a sharply undulating jet stream in general, to the melting Arctic sea ice, which is one of the most visible signs of a warming planet.

“Our research shows that northward swings, or ridges, in the jet stream have become more frequent in recent decades, exactly in the location where the large blocking high was parked when Sandy came along,” said Jennifer Francis, a meteorology professor at Rutgers University and one of the leading proponents of the Arctic connection hypothesis, in an email conversation. “These ridges favor the development of blocks, and they are just the type of pattern we expect to increase as the Arctic continues to warm much faster than the rest of the northern hemisphere.”

Marshall Shepherd, the president of the American Meteorological Society, said his graduate students have also investigated the Greenland block that was entrenched at the time that Sandy moved out of the tropics, concluding that it was “off the charts” in terms of its strength.

Andrew Kemp, a researcher at the University of Pennsylvania, said forthcoming research shows that sea level rise contributed to the coastal flooding from Sandy, but it was not the largest factor when compared to the timing of the high tide, the storm track, and other variables.

 Still, every inch counts, particularly when critical infrastructure is concerned.

"The risk, of course, is when flood heights exceed the physical thresholds of coastal defenses, and infrastructure is flooded. With all things being equal, sea level rise will make that happen more often," Kemp said in an email.

Regardless of whether global warming helped steer Sandy toward land, the coastal flooding it caused should have been an urgent call to action. The failure of coastal cities to implement any large-scale plans to boost climate and extreme-weather resilience in the wake of Sandy is troubling. It suggest New York, or any other coastal city, may get caught flat-footed once again.