By Phil Klotzbach, lead author of the Colorado State University (CSU) hurricane forecasting team, and I.I.I. non-resident scholar.
Five years ago this month (October 29), Superstorm (hurricane until a few hours before landfall) Sandy made landfall along the coast of New Jersey just northeast of Atlantic City. Sandy was one of the most devastating hurricanes to hit the northeast United States, causing more than 70 fatalities and $50 billion dollars in damage. It was the deadliest Northeast United States hurricane since Agnes (1972) and the 2nd most expensive United States hurricane on record behind Katrina (2005). While heavy rainfall and strong winds were part of Sandy’s legacy, the primary cause of the massive destruction and damage that occurred was due to high storm surge levels.
Sandy developed in the SW Caribbean on October 22 (Figure 1). This region is a typical hotbed for October Atlantic hurricanes. The system slowly intensified, eventually reaching hurricane strength before hitting Jamaica as a Category 1 hurricane. It briefly reached major hurricane strength (Category 3+ on the Saffir-Simpson Wind Scale) before making landfall in Cuba.
Figure 1: Track of Hurricane Sandy from its formation in the SW Caribbean until its dissipation in the northeast United States. Figure courtesy of National Hurricane Center.
Landfall in Cuba weakened Sandy somewhat, and the system began to undergo structural changes as it interacted with a large upper-level low pressure area. This upper-level low caused the inner core to lose intensity, but it also caused the storm to grow considerably in size. Sandy weakened to a tropical storm, but then vertical wind shear (the change in wind direction with height in the atmosphere), began to abate and Sandy was able to re-intensify to hurricane strength. The storm, however, retained its large, sprawling circulation. (Figure 2). Tropical storm-force winds extended more than 900 miles away from the center of the circulation as it approached the United States coast, making it the largest Atlantic hurricane on record (since 1988).
Figure 2: Infrared satellite imagery of Hurricane Sandy on October 29 showing the large, sprawling nature of its circulation. Figure courtesy of NOAA.
A large blocking high to the north of Sandy caused the storm to track to the northwest (Figure 3). Once Sandy had finished transiting the warm waters of the Gulf Stream and moved over cooler shelf waters near the New Jersey coast, it completed its transition into a post-tropical cyclone several hours before landfall.
Figure 3: Mid-level weather pattern causing the anomalous track that Hurricane Sandy took. Strong high pressure to the north of Sandy prevented recurvature and caused Sandy to track towards the northwest. Figure courtesy of National Hurricane Center.
While the maximum intensity at the time of its New Jersey landfall was 80 mph – equivalent to a Category 1 hurricane – the storm’s large size triggered huge amounts of storm surge. In addition, tides were running higher than normal, due to the lunar cycle; storm tide values shattered records in parts of New York City. At the Battery, Manhattan’s southernmost tip, the storm tide exceeded 14 feet, which was more than four feet higher than the previous record set during a winter storm in December 1992. Many other areas along the coast of New Jersey and in New York City reported storm surge levels of 5-8 feet from Sandy which combined with astronomical factors to cause massive inundation.
Sandy’s transition from hurricane to post-tropical cyclone immediately prior to landfall as well as the massive size of the system has helped us to refocus efforts in the five years since the storm to clearly delineate between the Saffir-Simpson Wind Scale category and potential impacts that the storm may generate. Just because a system transitions from a hurricane into a post-tropical system does not mean that its impacts have been ameliorated. While it has now been five years since Sandy’s landfall, it will forever be remembered in the northeast United States as an incredibly damaging storm.