Abstract:Based on the cloud track winds and the upper sounding winds,the first three terms ofright hand side of the fractionless barotropic vorticity equation, e. g. the relative vorticity advection, the planetary vorticity advection and the divergent term were calculated. The sum ofthese three terms gave an estimate of the local vorticity variation rate. Computations werecarried out to some tropical cyclone cases for the year 1998 over the region of the South China Sea and the Western Pacific. Results show that the local vorticity variation rate?ξ/?t hasspecial significance in indicating tropical cyclone movement,and it can indicate obviously botha steady track of tropical cyclone motion and a sudden turning on tropical cyclone movement.Tropical cyclones move generally toward the direction of maximum local vorticity variationrate. If ?ξ/?t has several maxima in the vicinity of tropical cyclone center, vector compositionmethod may give a mostly probable direction of tropical cyclone motion. In addition, just asthe steering current, there is an effective radius of interaction in ?ξ/?t field,within the effectiveradius the changes in ?ξ/?t field may have a direct influence to tropical cyclone motion.