A Statistical Analysis of Cyclones that Drive Storm Surge Extremes along the US East Coast

Abstract:

Storm surge, from both tropical cyclones (TCs) and extratropical cyclones (ETCs), is a major hazard that affects coastal areas. Storm surge properties can generally be explained by a combination of forcing from the atmosphere and details about the coastline and bathymetry. However, knowing how certain aspects of the atmosphere, in terms of cyclone characteristics, drive variability in storm surge can provide improved forecast guidance and help in projecting future changes in storm surge extremes. As such, this presentation explains the extent to which variability in storm surge is driven by the characteristics of the cyclones that cause storm surge. This study focuses on the Mid-Atlantic and Northeast regions along the US east coast, using historical observations of sea level and Lagrangian cyclone tracks.

The relative roles of surge-producing TCs and ETCs are first examined. For coastal cities north of North Carolina, ETCs pass within 250 km of a city 30 to 80 times more frequently than TCs. However, when TCs pass that close to a city, the likelihood that it generates extreme surge is over 80%, while less than 10% of ETCs within the same proximity generate extreme surge. We then test for relationships between storm surge amplitude and cyclone path, intensity, and propagation speed. For TCs, proximity is the strongest factor in determining if the TC will produce extreme surge. The track path of TCs is the second most important factor as TCs that track along the shoreline tend to produce significantly higher surge than TCs that recurve out to sea. For TCs whose track path meets certain criteria, we find that TC intensity, in terms of wind speed or central pressure, becomes a good predictor for surge amplitude. On the other hand, track paths of ETCs do not have as strong an impact on storm surge as TCs. However, for ETCs within 250 km of New York City, surge is found to be well-correlated with area-averaged 925 hPa wind speeds. ETCs that undergo rapid intensification, often referred to as bomb cyclones, are found to not be correlated with the strongest surge events. Propagation speed of ETCs does not appear to be a good predictor of surge on its own as extreme surge events are associated with varying propagation speeds. These cyclone characteristics will be examined to understand fully how variations in these characteristics influence storm surge.