资源环境科技发展态势分析平台

The track of tropical cyclones (TCs) formed in the South China Sea (SCS) can be divided into eastward and westward directions. Significant decadal variation during 1980-2020 only exists in the number of eastward-moving TCs, especially during July-September, with 47% TCs moving eastward during 1994-2004 (Period II), 22% during 1980-1993 (Period I) and only 15% during 2005-2020 (Period III).

This decadal change is related to the zonal shift of Western Pacific Subtropical High (WPSH). An eastward-retreated WPSH during 1994-2004 leads to upward motion and westerly flow anomaly over the northern SCS, and therefore favors TC genesis and eastward motion. The eastward-retreated WPSH is associated with a warm SST anomaly over the tropical western-central Pacific which induces a cyclonic flow and weakens the WPSH. With the weaker modulation of WPSH, stronger intraseasonal oscillation (ISO) in the SCS during Period II favors eastward-moving TCs due to the westerly flow associated with the ISO.