Statistical Characteristics and Mechanistic Analysis of Suddenly Reversed Tropical Cyclones over the Western North Pacific Ocean

Based on best track data of tropical cyclones (TCs) from the Japan Meteorological Agency, the characteristics of suddenly reversed TCs (SRTCs), which have turning angles usually approaching 180 degrees, are statistically analyzed from 1949 to 2011 over the western North Pacific Ocean. The typical large-scale circulation patterns of SRTCs are investigated using reanalysis data and dynamical composite analysis. Results show that turnings mainly occur in low latitudes between 10 degrees N and 20 degrees N, and mainly west of 135 degrees E. The majority of SRTCs reach their peak intensity at, or slightly before, the turning time and subsequently decrease at some variable rate. Specifically, SRTCs are divided into four types, each containing two groups (i.e. eight groups in total) in terms of the moving-direction changes. The moving speed of all SRTC types except the south-north type decreases to its lowest during the 24 h, corresponding to a significant reduction in the primary steering components. According to the analysis of the 13 typical flow patterns found in this study, we suggest that sudden track changes are caused by the reversal steering flow. The original balance of the background flow patterns are broken up by new systems, e.g. binary TCs or dispersion-induced anticyclones. Additionally, sudden track changes are often due to double ridge variations of the subtropical high or weakened/strengthened high pressure in the east and west, respectively.