Rapid wave modeling of severe historical extratropical cyclones off the Northeastern United States

Storms play a significant role in coastal zone hydrodynamics, morphodynamics and flooding. The US Northeast is influenced by both extratropical (e.g. nor'easters) and tropical cyclones, which produce extreme winds, storm surges and waves, and as a result erosion and coastal damage. In this study, simulations of 100 of the most severe historical extratropical cyclones in this region were used to evaluate a new, rapid numerical wave model that is a candidate model for ensemble forecasting and hazard assessment. The main tool used was a coupled hydrodynamic-wave model, forced by wind and pressure from preexisting meteorological reanalysis datasets. The coupled models were the Stevens institute Estuarine and Coastal Ocean hydrodynamic Model (sECOM) and the Mellor et al. (2008) (hereafter MDO) wave model, and includes several important physical interactions (e.g. wave setup). Wave model results were compared to offshore buoy observational data from 1980 to 2012, and a sensitivity analysis was used to evaluate important model parameters. Results show that the wave model is very accurate for wave height (Hs), with an average RMSE of 0.92 m and skill ranging from 0.7 to 0.9. Results were less accurate for average wave period (Tavg), with an average RMSE of 1.97 s and skill ranging from 0.5 to 0.7. However, a comparison with a more widely used existing rapid wave model shows a substantial improvement over those Tavg results. Large waves approach the coast in Massachusetts Bay during extratropical cyclones, leading to important wave impacts including setup, and modeled storm surge is shown to have good accuracy and no bias at Boston. These results demonstrate the strengths and weaknesses of the model for rapid simulations of waves under history's most extreme extratropical cyclones, and the evaluation results and sensitivity analysis are used to suggest its appropriate uses and possible avenues of improvement.