Exploring Water Level Sensitivity for Metropolitan New York during Sandy (2012) Using Ensemble Storm Surge Simulations

Abstract

This paper describes storm surge simulations made for Sandy (2012) for the Metropolitan New York (NYC) area using the Advanced Circulation (ADCIRC) model forced by the Weather Research and Forecasting (WRF) model. The atmospheric forecast uncertainty was quantified using 11-members from an atmospheric Ensemble Kalman Filter (EnKF) system. A control WRF member re-initialized every 24 h demonstrated the capability of the WRF-ADCIRC models to realistically simulate the 2.83 m surge and 4.40 m storm tide (surge + astronomical tide) above mean lower low water (MLLW) for NYC. Starting about four days before landfall, an ensemble of model runs based on the 11 "best" meteorological predictions illustrate how modest changes in the track (20-100 km) and winds (3-5 m s flooding was not the worst case for this particular event. Had Sandy made landfall at differing times, locations and stages of the tide, peak water levels could have been up to 0.5 m higher than experienced.

A validated tropical-extratropical flood hazard assessment for New York Harbor

“…We use a wave‐slope sensitive parameterization [ Taylor and Yelland , ], and find that the best fit ceiling value is 0.0035, for fitting historical TC storm tides (measured with RMS error) with our simplified wind fields. Prior studies in the area have used the Garratt [] parameterization with ceilings of 0.0025 [ Lin et al ., ], 0.0030 [ Wang et al ., ], 0.0035 [ FEMA , ], and with no ceiling [ Colle et al ., ]. Misalignment of wind and swell can be a source of higher drag [e.g., Holthuijsen et al ., ], but these processes are not well understood, and other factors such as storm translation speed are important [e.g., Reichl et al ., ] and not represented by existing wind speed‐based drag parameterizations.…”

“…Rare severe storm tide events are outside the normal range of variability, and thus forecast-oriented ocean models may be tuned toward normal conditions or annually recurring storm conditions. In addition, atmospheric forcing data are typically a strong determinant of storm tide modeling accuracy [e.g., Colle et al, 2015;Orton et al, 2012]. Historical meteorological reanalyses are available for the ETCs [FEMA, 2014a], but simplified wind and pressure fields are used for the TCs, raising the possibility that oversimplification would lead to biases in the storm tide simulations.…”

Impact of Tropical Cyclone Landfall Angle on Storm Surge Along the Mid‐Atlantic Bight

“…ADCIRC has been implemented for various coastal studies in the region of interest along the NJ-NY coastal area (Cialone et al, 2017;Colle et al, 2015;Lin et al, 2010;Ramos-Valle et al, 2018;Yin et al, 2016). The ADCIRC model uses a finite-element unstructured triangular grid allowing for higher resolution near the coast and coarser resolution in the deep ocean.…”

New York City Panel on Climate Change 2019 Report Chapter 4: Coastal Flooding

“…Wind is the primary factor governing storm surge, through its speed and the distance over which it blows, the wind fetch. The height and timing of high tide relative to the peak storm surge is also an doi: 10.1111/nyas.14011 important factor for New York City coastal flooding (e.g., Colle et al, 2015;Colle et al, 2008;Georgas et al, 2014;Kemp and Horton, 2013). Storm tide can be defined as the combination of tide level and storm surge, measured as a value above a given year's MSL.…”

“…Sandy in 2012 was a “hybrid” storm type, in that it was transitioning from a tropical to an extratropical cyclone while approaching landfall. It generated the highest recorded water level at New York Harbor in at least 300 years, due to sustained strong easterly winds and a storm surge maximum coinciding with high tide (Colle et al ., ; Orton et al ., ).…”