Thirty-four years of Hawaii wave hindcast from downscaling of climate forecast system reanalysis

Abstract

10The complex wave climate of Hawaii includes a mix of seasonal swells and wind waves from all 11 directions across the Pacific. Numerical hindcasting from surface winds provides essential space-12 time information to complement buoy and satellite observations for studies of the marine 13 environment. We utilize WAVEWATCH III and SWAN (Simulating WAves Nearshore) in a 14 nested grid system to model basin-wide processes as well as high-resolution wave conditions 15 around the Hawaiian Islands from 1979 to 2013. The wind forcing includes the Climate Forecast 16 System Reanalysis (CFSR) for the globe and downscaled regional winds from the Weather 17 Research and Forecasting (WRF) model. Long-term in-situ buoy measurements and remotely-18 sensed wind speeds and wave heights allow thorough assessment of the modeling approach and 19 the data products for practical application. The high-resolution WRF winds, which include 20 orographic and land-surface effects, are validated with QuickSCAT observations from 2000 to 21 2009. The wave hindcast reproduces the spatial patterns of swell and wind wave events detected 22 by altimeters on multiple platforms between 1991 and 2009 as well as the seasonal variations 23 * Corresponding Aurthor: 2 recorded at 16 offshore and nearshore buoys around the Hawaiian Islands from 1979 to 2013. 24 The hindcast captures heightened seas in interisland channels and around prominent headlands, 25 but tends to overestimate the heights of approaching northwest swells and give lower estimations 26 in sheltered areas. The validated high-resolution hindcast sets a baseline for future improvement 27 of spectral wave models. 28 Research and Forecasting model 30 1. Introduction 31 Hawaii has unique wave climate associated with its North Central Pacific location and 32 massive archipelago. Figure 1 provides a location map to illustrate the prominent wave regimes 33 and geographical features. Extratropical storms near the Kuril and Aleutian Islands generate 34 swells toward Hawaii from the northwest to north during the boreal winter. The south facing 35 shores experience moderate swells from the year-round Southern Hemisphere Westerlies that are 36 augmented by mid-latitude cyclones in the boreal summer. The persistent trade winds generate 37 waves from the northeast to east throughout the year, while subtropical storms during the winter 38 and passing cold fronts can generate waves from all directions. The steep volcanic mountains 39 speed up the wind flows in the channels and create prominent wakes leeward of the Hawaiian 40Islands (Yang et al., 2005; Nguyen et al., 2010; Hitzl et al, 2014). These localized wind flows 41 together with island sheltering create regional wave patterns with large spatial and temporal 42 variations (Aucan, 2006; Caldwell et al., 2009; Stopa et al., 2011). 43There are increasing demands for long-term wave data in support of ocean renewable energy 44 planning, marine ecosystem assessment, shoreline management, and infrastructure development 45 in Hawaii. Altimeters aboa...

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