Analyses in Errors and Their Causes of Chinese Typhoon Track Operational Forecasts

Forecast errors for different typhoon types,typhoon landfall position and time,typhoon locating in different position from coastline,typhoon landfall in East China and South China are issued based on typhoon track operational forecast data and best-track data in the western North Pacific(the South China Sea is included)provided by China Meteorological Administration(CMA)from 2005 to 2009.The results show that typhoon track forecast during 2005-2009 is more skillful than from 1999 to 2003.Average typhoon forecast bias in the South China Sea(SCS)is larger than in western North Pacific(WNP).Unusual typhoon track mainly occurred in the SCS and their forecast errors are smaller than usual typhoon tracks for 24 h,48 h and 72 h forecast periods.The forecast error is the largest during typhoon approaching coastline period among typhoon far away from coastline,approaching coastline and landfall later periods and it is larger for typhoon landfall in South China than in East China during same period.The average forecast errors are 71.1 km,122.6 km and 210.6 km of typhoon landfall position for 24 h,48 h and 72 h forecast periods,respectively.Timing errors of 70%landfall typhoons demonstrate an early bias of 8 h and 12 h against forecast landfall for 48 h and 72 h forecast periods.Compared with large-scale steering flow to typhoon movement and 24 h forecast errors,the results also show that there are different bias between large-scale steering flow and typhoon movement among three typical landfall typhoon tracks and relationships between these biases and 24 h typhoon forecast track errors.Parabolic typhoon movements in the SCS have the largest bias between the steering flow and typhoon movement,but have the smallest forecast errors;the largest forecast error for west to northwestward moving typhoon is not corresponding to its smaller bias between steering flow and typhoon movement,which may be related to low skillful forecast of large-scale circulation.The forecast error of typhoon landfall in East China is smaller than in South China, which is consistent with the bias of the former between steering flow and typhoon movement being smaller than the latter.