Multi-scale characteristics of an extreme rain event in Shandong Province, produced by Typhoon Lekima (2019)

Abstract

Super Typhoon Lekima (2019) is the fifth strongest typhoon to make landfall in mainland China since 1949. After its landfall, Typhoon Lekima moved northward along the coastline, resulting in an extreme rain event in Shandong Province that caused the highest precipitation in available meteorological records. A Weather Research and Forecasting (WRF) model simulation that properly produces the track and intensity of Typhoon Lekima and the spatio-temporal evolution of rainfall is used to analyze the multi-scale characteristics of the extreme rain event. The results show that different from the typhoon precipitation which occurred at low latitudes, the extreme rain event that occurred in mid-latitudes was influenced by the interactions of mid-latitude synoptic systems and typhoon circulation, especially with five mesoscale rainbands. The mid-latitude synoptic systems, mainly including the upper-tropospheric jet, the western North Pacific subtropical high, the mid-latitude trough, the low-level jets, and Typhoon Krosa (2019), allowed Typhoon Lekima to maintain its intensity after landfall and provided favorable kinematic, thermodynamic, and moisture conditions for the heavy rainfall in Shandong. Based on the evolution of the mesoscale rainbands, the extreme rain event can be divided into three stages. The first stage can be classified as distant rainfall, which was affected by two convective rainbands associated with boundary-layer processes. The second stage had the highest precipitation, featuring the formation of a frontal zone in Shandong, interacting with Typhoon Lekima. The third stage had weakened rainfall and was directly influenced by the spiral rainband of Typhoon Lekima.