Changes in Tropical-Cyclone Translation Speed over the Western North Pacific

The trend of tropical-cyclone (TC) translation speed is a hot topic recently. Changes in TC translation speed during 1949-2017 over the western North Pacific are analyzed using two best-track datasets here. The TC translation speed decreased during 1949-2017, but there was no significant trend after 1981. The TC translation speed also changes with latitude and intensity. In the tropical ocean, TC translation speed decreased by 5.9% during 69-year recording period. North of 23.5 degrees N, the changes in translation speed is highly consistent with the latitude of TC occurrence. The translation speed of tropical depressions showed no significant trend during the period 1949-2017, but the translation speed of typhoons decreased over the 69-year recording period. The period 1949-1981 contributed most of the slowdown trend. There also was an increase in the frequency of typhoons with translation speed slower than 6 m/s. The decrease of translation speed of typhoons before 1981 was likely caused by the weakening of the summertime tropical circulation.