Impact of tropical cyclones on interannual rainfall variability over the western North Pacific

The impacts of tropical cyclone (TC) on the seasonal and interannual variability of the total rainfall over the western North Pacific (WNP) are investigated. The TC rainfall at a station is estimated by using station rainfall data and an empirical influential function of the distance between TC center and the station. Along 10° N, where the WNP monsoon trough is located, the TC rain ratio is relatively low: a maximum of 35 % at Guam during October and November. In contrast, along 125° E and north 15° N, where the non TC rainfall is small under the influence of the WNP subtropical high, more than 50 % of TC rain ratios are commonly found from July to November. In the summer of El Niño developing year, the increase of the total seasonal rainfall along 10° N is dominantly caused by the increase of the TC rainfall. In the ensuing autumn, the TC rainfall shifts eastward and the decrease of the TC rainfall has a dominant impact to the total rainfall to the east of 140° E, although large-scale environment is unfavorable for developing local convections, the westward passage of TCs enhances TC rainfall which offsets the decrease of non-TC rainfall.