Significant anomalous tracks were observed when the severe tropical storm Goni (0907) and typhoon Morakot (0908) in September 2009 were evaluated in short distances. The relationship between the two is regarded as a case of binary interaction. Based on an MM5 model (fifth-generation mesoscale model of Pennsylvania State University-National Center for Atmospheric Research), in this study a series of sensitivity experiments were designed to determine the binary interaction between them. The sensitivity of the storm characteristics to the binary interaction was demonstrated through modeling experiments with different TC intensities and sizes based on the bogus vortices initialization. Furthermore, the contributions of large-scale environmental flow and the effects of interaction between the motions of the cyclones were distinguished by numerical experiments using only one of the TC vortices. Results from these experiments show that Morakot (0908) had a greater impact on the motion of Goni (0907), whereas Goni (0907) had a relatively limited impact on Morakot (0908). At the upper level, the northeasterly jet flow in the third quadrant of Morakot (0908) enhanced the upper-level divergence of Goni (0907) and had an important role in maintaining and increasing Goni's (0907) intensity. And at the lower level, Morakot (0908), with strong convergence and ascending airflow, made a stable transport channel of southwesterly warm and wet flow, thus supporting the lower-level water vapor convergence of Goni (0907). Goni (0907), which was located upriver of the southwesterly flow, intercepted part of the water vapor transportation in the southwesterly flow, causing the water vapor convergence to strengthen while the water vapor convergence of Morakot (0908) weakened.