Central to tropical cyclogenesis is the changing behavior of moist convection as the cyclone evolves. Based on a cumulus ensemble model run in weak temperature gradient mode, we suggest that the mid-level vortex created by early-stage convection stabilizes the environment in way that favors further development. In particular, modeled convection occurring in the more stable environment produces heavy rainfall and concentrated inflow at low levels. Such inflow is needed for the development of the low-level vortex characteristic of warm-core tropical cyclones. The increase in humidity which is typical of developing cyclones also increases convective rainfall, but it does not act to concentrate the inflow at low levels.