The sensitivity of tropical cyclone forecast to changes in the initial state is examined using powerful singular vector diagnostics from a global weather forecast model. These techniques reveal the complex impact of both the local and remote environment on the typhoons. We demonstrate how the analyzed position and forecast of one typhoon can have a significant impact on the forecast of a second typhoon, even at distances up to 1861 km. These results highlight the difficulty of tropical cyclone prediction, especially when remote forcing plays a significant role in tropical cyclone motion.