Understanding the Unusual Track of Typhoon Lionrock (2016)

Abstract

The unusual movement of Typhoon Lionrock (2016) that posed great challenges for operational numerical predictions was investigated. Analysis of the steering flow at different levels shows that Lionrock’s southwestward motion before 25 August was mainly controlled by the upper-level steering, and the dominant steering shifted to lower levels as the storm turned northeastward abruptly afterward. To examine the influence of the environmental flow on this major turning of Lionrock, three numerical simulations are conducted using the Weather Research and Forecasting (WRF) Model with different starting times. The study indicates that the initial southwestward movement of Lionrock is attributed to the westward extension of the mid- to upper-level subtropical high, and the later turning to northeast is caused by the low-level southwesterly flow associated with the monsoon gyre northeast of Lionrock. In an experiment in which the monsoon gyre is removed from the initial and boundary fields, Lionrock continues its southwestward movement without turning northeastward. This result suggests that the transition of the steering from high to low levels plays a crucial role in the major turning of Lionrock. More sensitivity experiments with modifications of the initial and/or the boundary conditions indicate a low predictability of Lionrock’s major turning.