Abstract : To improve tropical cyclone structure and intensity prediction through a research program combining high-resolution modeling and detailed observational studies to investigate physical processes by which the structure and intensity of a tropical cyclone are modified. The objective is to investigate the physical processes that occur as a tropical cyclone interacts with the environment such that intensity and structure changes occur. Specific interactions being studied are with baroclinic environments in the midlatitudes during extratropical transition. During extratropical transition, radical changes to the storm structure occur as vertical wind shear and intruding cold, dry air from the midlatitudes erode the warm core. Re-intensification to a strong midlatitude system is possible. In cases in which forecast models poorly predicted the motion and re-intensification of the storm during these transitional periods, better understanding of these processes should improve motion and intensity forecasts.