Influence of Tropical Cyclones that Develop from Different Type Environments on the Characteristics of Landfall, Intensity, and Rainfall over the Asian Coast

In this study, a non-hierarchical cluster analysis, k-means clustering, is used to classify the tropical cyclones (TCs) that develop from monsoon and easterly environments in the western North Pacific. During Jul-Oct 1981-2009, 82 and 131 TCs that develop from easterly and monsoon environments are identified, respectively. Landfall characteristics for TCs from each developmental environment are analyzed for the Asian Coast, defined as the coastline from the Philippines, Indochina, China Mainland, Taiwan, North and South Korea to Japan. Only the first time a TC makes landfall is considered. The average percentage of TCs that make landfall is 54 % for TCs developing from easterly environments and 66 % for TCs developing from monsoon environments. The intensity of TC landfall is positively correlated with the distance from the location of TC formation to the coast, which is statistically significant for TCs developing from monsoon and easterly environments. Because the average formation location of TCs developing from easterly environments is to the east of that from monsoon environments, TCs developing from easterly environments tend to have a lower landfall percentage, stronger maximum intensity in their lifetime, and stronger intensity at TC landfall. On a regional scale, TCs developing from monsoon environments have a higher probability of landfall over Taiwan, south of China, and Indochina than TCs developing from easterly environments, while TCs developing from easterly environments have a higher probability of landfall over the Philippines, central China (i.e., ZheJiang area), and Japan.

Regarding the rainfall pattern of TC landfall, although the rainfall area associated with TC landfall is larger for TCs developing from monsoon environments than that from easterly environments, the rainfall value near the TC center is not significantly different. However, because the pattern of monsoon and easterly environments is affected by the El Niño-Southern Oscillation (ENSO), the number, percentage, location, and intensity of TC landfall are also influenced by ENSO modulations. For TCs developing from monsoon environments, the percentage of TC landfall is higher during La Niña years, but the landfall intensity is not different between El Niño, La Niña, and normal years. For TCs developing from easterly environments, the annual number of TC landfall is higher and landfall intensity is stronger during normal years, and the landfall intensity is weaker during La Niña years.