Abstract:The typhoon heavy rainfall can easily induce an extreme weather event, and it is difficult to predict. In this study, we investigate the statistical relationship between the precipitation extreme forecast index (EFI) from ECMWF ensemble forecast system and the observed typhoon heavy rainfall with 13 typhoons that affected East China during 2013-2017. The results show that the EFI is a good indicator to predict the typhoon rainfall. Different EFI thresholds should be used as the reference for precipitation of rainstorm area. Overall, the possibility of heavy rainfall occurrence increases with the increase of EFI. The threshold of EFI gradually decreases when the forecast lead time increases. With the criteria of TS maximization, the EFI thresholds for different lead times and different storm levels are estimated in East China. Higher TS scores and reasonable BS scores are obtained when the thresholds are 0.7/0.8, 0.7, 0.6, 0.5 for rainstorm precipitation with lead time of 24, 48, 72, 96 h, respectively. Therefore, they can be used as EFI thresholds for different lead times. Significant positive correlation is found between the EFI and the climatic percentile of precipitation. The larger precipitation percentile appears when the EFI increases. When the EFI is prominently large, the typhoon rainfall can be estimated with the corresponding climatic percentile of observed rainfall. The EFI is a good indicator for extreme rainfall, and can predict the situation 3-5 days in advance.