By Kim Smiley
Hurricane Sandy pummeled the Mid-Atlantic region of the United States on October 29th and 30th, 2012, leaving more than eight million people without electricity, causing massive flooding and killing over 110 people. The damage done by this storm was massive and economic impacts have been predicted to be as high as 50 billion dollars.
Why was Sandy so devastating? This question can be answered by building a Cause Map, an intuitive format for performing a root cause analysis. A Cause Map is a useful tool for breaking down this complicated issue and can help explain why this storm was unique.
In this example, there are a number of things that combined to made Sandy a unique and especially dangerous storm. First off, Sandy wasn’t just a normal hurricane. As hurricane Sandy moved to the north it converged with other weather systems turning into a hybrid storm. This hybrid storm brought with it a combination of extreme summer weather (strong winds with heavy rains) and winter weather (cold temperatures and snow). Unusual timing of the different weather systems helped this superstorm form. Hurricane Sandy hit very late in hurricane system and cold air sweeping down from Canada was colder than typical for this time of year, a combination that proved deadly. The nature of these converging weather patterns also made Sandy a very slow moving storm so that areas experienced higher rain fall and more damage than they might have with a faster moving system.
Normal hurricanes are powered by the warm, moist tropical air and weaken as they travel north. They also typically turn to the right and head out to sea. When Sandy converged with the other systems it became an extra-tropical cyclone and actually strengthened as it hit shore. The effects of these other weather systems also turned the storm left onto land and it took an unusual path over some of the most heavily populated areas of the US, including NYC, intensifying the impact of the storm.
The timing of Sandy also impacted the peak flood levels. Sandy hit during a full moon when tides are at the highest point of the month. During a full moon, the effects of the moon’s gravity are felt the strongest so tides are higher. The high winds created by Sandy combined with the full moon resulted in a massive storm surge.
Sandy truly was a Superstorm. Weather systems that normally don’t exist at the same time converged to create a massive storm that moved in a usual path over one of the most heavily populated regions in the US. And the storm hit at the worst time of the month for flooding.