A METHOD FOR PREDICTING SHORT-AND MID-RANGE TURNING AND ACCELERATION MOTION TREND OF TROPICAL CYCLONES OVER THE SOUTH CHINA SEA

An approach is proposed for predicting turning and acceleration motion trend of the tropical cyclones over the South China Sea for 72 h in the extrapolated track coordinates.Cross-track(CT) and along-track(AT) components are defined according to the persistently extrapolated track coodinates based on observed positions at the initial and past 24 h times.A kind of straight-forward measure may be provided with CT and AT components for typhoon turning motion and acceleration motion.Canonical correlation analysis(CCA) is performed to reveal the correlaotions between tropical cyclone tracks and environmental 500 hPa geopotential height fields.A stepwise discriminate analysis technique is adopted to derive the classification functions of the respective three categories for AT and CT components.Especially,categorical combinations of CT and AT components are divided into possible 9 regions corresponding with tropical cyclone behaviors.Not only can 9 motion trends of a tropical cyclone be predicted,but also the location and its maximum error at least in certain direction are available.The perfect prediction(PP) verifications indicate that the percent corrects for the CT and AT categories are 67% and 69% in the independent samples,73% and 53% in the dependent samples,respectively,higher than that of 33.3% for random chance;moreover,the rate for successfully forecasting that in which one of the nine regions the tropical cyclones will fall at 72 h is about 40%,also higher than the stochastic probability of 11%.The method has been proved to be skillful and promising.