LAUSR

Typhoon Sanba (2012), the strongest tropical cyclone (TC) of the year worldwide, moved northward almost along 130° longitude during its lifetime and passed through different background flows from low to high latitudes. The steering flows with different time scales for Sanba are retrieved using the NCEP reanalysis data with the total wind field separated into: a mean state, an interannual component, an intraseasonal component, and a synoptic component. Our analysis indicates that the intraseasonal time-scale wave train (WT) with east–west oriented circulations made the largest contribution to the movement of Sanba. The effects of the environmental steering with different time scales on Sanba’s movement are investigated with numerical simulations using the Weather Research and Forecasting (WRF) model. In the control simulation, total fields from the NCEP reanalysis are used as initial and boundary conditions, and the northward motion of Sanba is well captured. In sensitivity experiments, each of the intraseasonal and interannual components is removed one at a time. The steering vectors associated with these time scales can explain their influences on the movement of Sanba in the experiments. Vorticity budget analyses indicate that the horizontal vorticity advection made the largest contribution to the movement of the storm.