An investigation of recent decadal-scale storm events in the eastern Irish Sea

The Proudman Oceanographic Laboratory Coastal Modelling System coupled to the WAve Model (POLCOMS-WAM) modeling system has been used to model combined tides, surges, waves, and wave-current interaction in the Irish Sea on a 1.85 km grid. A method for data analysis is presented to determine what factors and interactions contribute to extreme conditions in a region of interest. An 11 year hindcast (1996-2006) has been performed to investigate the meteorological conditions that cause extreme surge and/or wave conditions in Liverpool Bay. A one-way nested model approach was used. For waves, a 1° North Atlantic WAM model forces the boundary of the Irish Sea model, driven by ERA-40 wind (∼1° resolution every 6 h). To capture the external surge generated outside of the Irish Sea, the (1/9° × 1/6°) Proudman Operational surge model extending to the continental shelf edge was run for tide and surge and was forced by Met Office mesoscale winds (∼12 km resolution every hour). The data implied that the largest surges at Liverpool are generally driven by winds from the south to the west while the largest waves are forced by winds from the west to the northwest. The worst storm conditions in Liverpool Bay result under southwesterly wind conditions that veer to the west. The large tidal range in the region acts to enhance the impact of the surge through tide-surge interaction. Moreover, the highest water levels in Liverpool Bay are in response to southwesterly winds combined with high-water spring tide. Even though no significant surge occurs at this time, the flood threat is at its greatest.