Impact of track forecast error on tropical cyclone quantitative precipitation forecasts over the coastal region of China

Qualitative and quantitative assessments of the impact of track forecast error on tropical cyclone (TC) quantitative precipitation forecasts (QPFs) are presented in this study. The original and track-error-corrected QPFs extracted from the Global Forecast System (GFS) of 52 TCs over the coastal region of China during 2015-2017 were compared with the Global Precipitation Measurement (GPM) observations. The track forecast error was corrected by shifting the QPF according to the difference between the forecasted and observed TC centers. Qualitative evaluations revealed that large track forecast error tends to cause severe under-forecast of total rainfall volume over a region. Quantitative assessments showed that the impact of track forecast error generally increases with track forecast error up to 500 km. The rapid decline of QPF skill with lead time is mainly attributed to the fast-growing track forecast error. Track forecast error has large impact on moderate to heavy rainfall and little impact on extremely heavy rainfall. Based on the assessments, a new operational post-processing method was developed to reduce the impact of track forecast error on QPFs from numerical models. The new technique was able to improve the TC QPFs in general and especially at longer lead times.