Heo, K.-Y., Shim, J.-S., Kwon, J.-I., Jeong, J.-Y., Park, K.-S. and Choi, J.-W., 2013. Abnormal storm waves around the Korean Peninsula: A case study of an extratropical explosive cyclone over East Sea.On April 3, 2012, an extratropical explosive cyclone developed over East Sea, producing heavy rainfall and strong winds. This cyclone produced maximum wind speeds of up to around 21 m s−1 over the ocean around Korea. As the explosive cyclone developed rapidly from 00 UTC April 3, 2012, it began to affect the coastal areas, and abnormal storm waves were generated by the strong wind. The observed maximum wave heights and periods around Korea were 11.1 m and 9.1 s at Chilbaldo, 12.0 m and 9.1 s at Marado, and 13.7 m, and 5.8 s at Ulleungdo in the period 04–10 UTC April 3, 2012. The objectives of this study are to investigate the mechanisms and conditions favorable for the development of the explosive cyclone, and to investigate the influence of the cyclone on the abnormal storm waves. To achieve the above objectives, numerical studies are conducted using the Weather Research and Forecasting (WRF) model as an atmospheric model and the open ocean wave model WAM. The explosive cyclone is amplified by latent heat release as well as the formation of an upper-level cut-off low, which resulted in the rapid intensification of the cyclone; while surface heat fluxes had a lesser contribution to the explosion of the cyclone. In situ meteorological observation data and wave data from buoy measurements for this event are available for comparison and validation. The comparisons show that the WRF and WAM models can accurately predict the wind speed and wave height.