Rainy seasons in the nansei-shotou (southwest islands) of japan

The seasonal changes of precipitation in the Nansei-Shotou (Southwest Islands) of Japan are investigated using 20-year (1979-98) averaged pentad rainfall data. Four major climatological rainy seasons are recognized over this region. 1) The spring rainy season from mid-March to early May, more obvious in the northern part, caused by extratropical cyclone and frontal systems. 2) The early summer rainy season from mid-May to mid-June corresponding to Bai-u, of which onset, peak and end migrate northward. 3) The late summer rainy season from late July to late August, more obvious in the southern part, caused mainly by typhoons passing over this region westward or northward. 4) The autumnal rainy season from mid-September to late September, influenced by typhoons but those migrating northeastward recurving around this region. The influence of Japanese Akisame (Autumnal rain) frontal zone is recognized only in the northern part