Hurricane Juan generated huge, complex waves in the Northwest Atlantic and in coastal waters off Nova Scotia in late September 2003. This study focuses on the accurate, high-precision simulation of waves generated by Hurricane Juan in coastal waters through the application of the WAVEWATCH III (WW3) and SWAN wave models. Cyclone-generated waves in coastal waters are very complex compared with those in offshore and ocean regions. Two issues are addressed that influence the accurate, high-precision simulation of cyclone-generated waves in coastal waters:

  1. the SWAN model's numerical sensitivity during nonstationary simulations in coastal waters; and

  2. the incoming two-dimensional wave spectral pattern at the model boundaries.

Introduction

A detailed discussion of Hurricane Juan's development is given by Fogarty et al. (2006). Juan reached hurricane strength by 1200 Coordinated Universal Time (UTC) on September 26, 2003 near Bermuda and moved northward and then northwestward as a subtropical ridge, which was to the northeast of its location, extended to the west. It reached a maximum wind intensity of 46 m/s at 2100 UTC on September 27 and then turned northward towards Nova Scotia with increasing propagation speed. By 1800 UTC on September 28, Juan was north of the Gulf Stream, and its intensity began to weaken due to the cooler continental shelf waters south of Nova Scotia. However, because of its accelerating translation speed, Juan spent little time over these cooler waters and therefore did not weaken significantly. Juan made landfall near Halifax (0300 UTC on September 29) with sustained winds of 44 m/s. Table 1 gives the detailed storm characteristics of Juan and the best track for Juan from 0300 UTC on September 27 to 0900 UTC on September 29 (Avila, 2012). Figure 1 depicts the variation in the translation speed for Juan, showing a dramatic increase in speed from 2.28 m/s to 20 m/s. This acceleration in translation speed, typical of extratropical hurricanes, allowed the generation of huge, complex waves in deep ocean and coastal areas.

It is well known that the operational forecasts of waves generated by Hurricane Juan tended to have poor quality. For a discussion of the weather forecasts, see McTaggart-Cowan et al. (2006). Errors in forecasted winds led to large errors in forecasted waves (Padilla et al., 2007). Therefore, Xu et al. (2007) carried out a study of these waves. They improved the simulation of Juan's winds by developing a methodology to blend and interpolate simulated winds into wind observations. Moreover, in this approach, they considered the translation speed effect, implementing a high wind speed modulation of the drag coefficient. In this manner, they were able to notably improve the accuracy of the simulated waves. However, problems still remain, especially for waves generated by Juan in coastal shallow water areas, even if the spatial and spectral resolutions are notably increased compared to those of the grids used in operational forecasting. This study focuses on the high-precision simulation of waves generated by Hurricane Juan in shallow waters. Our approach is to explore the nonstationary computation method and to improve the boundary conditions at the edge of the integration grid through the use of observed two-dimensional spectra. Related studies by Perrie et al. (2010a, 2010b, 2013) considered the impact of different parameterizations of nonlinear wave-wave interactions on simulations of waves generated by Juan over the deepwater portion of its life cycle.

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