Abstract:On 22 June 2017, an extreme warm-sector rainfall event hit the western coastal area of South China, during which Jinjiang Station observed a maximum cumulative rainfall of 562.5 mm in 24 hours which broke many local historical records. This paper analyzes the synoptic background, synoptic-scale triggering and maintenance mechanisms as well as evolution of the precipitation characteristics in this extreme rainfall event by using the NCEP/NCAR reanalysis data and multi-source observations. The results show that this extreme rainfall occurred under the condition of the low-level warm and humid southerly airflow. The updraft movement caused by the double low-level jets was the main synoptic-scale triggering mechanism. The upper-level jet also provided favorable unstable energy and water vapor. The outflow boundary generated by weak cold pool maintained for a long time at the same place and continuously lifted the warm and humid unstable air, resulting in extreme cumulative rainfall. During the whole rainfall process, the convective structure showed a low centroid. In the mature stage of convection, the average particle sizes of near-surface in the Jinjiang and Gangmei areas were relatively alike. The rainfall efficiency of Jinjiang was higher than that of Gangmei, which was mainly reflected in the larger number concentration of raindrops.