Variations and prediction of the annual number of tropical cyclones affecting Korea and Japan

This paper investigates the factors affecting the annual number of tropical cyclones (TCs) passing within 100 km of the coast of Korea and Japan (KJ). Using a training set consisting of the coefficients of empirical orthogonal functions of these factors between 1965 and 2005, equations are derived to predict the annual number of these TCs over the whole season in April, and to update this prediction for the July-November (JN) season in June. Results show that the El Niño-Southern Oscillation (ENSO) plays a key role in determining the behaviour of TCs affecting KJ, with more TCs affecting the region during El Niño and less during La Niña. This difference can be attributed to ENSO modifying the flow patterns, which in turn affects TC behaviour. The prediction equations suggest that the 500-hPa geopotential height is more important in determining the number of TCs affecting KJ in the whole season, while both the 850-hPa geopotential height and 850-hPa vorticity play a role in the JN season. Both prediction schemes are able to produce acceptable results, with forecast skills of 42.3 and 33.3% over climatology for the whole, and JN seasons, respectively. The predicted TC number for 2006, 2007, and 2008 are also mostly accurate to within one standard deviation of the observed number. © 2010 Royal Meteorological Society.