Humping formation presents a key challenge in high-speed laser welding. This phenomenon significantly degrades seam quality and its mechanical-technological properties. Therefore, numerous studies have focused on clarifying the underlying fundamentals, particularly concerning the dynamic behaviour of the melt pool. However, the dynamics of the melt pool are primarily driven by the keyhole dynamics, relating to the material evaporation. Following, this study focuses on the characterization of the influence of melt-vapor-interaction on humping formation in laser welding of high-alloy steel AISI 304 (1.4301). Using core-to-ring laser intensities, the impact of spatial and temporal evaporation on resulting keyhole dynamics was revealed using a multiphysics Mass-of-Fluid simulation model. By correlating high-speed synchrotron X-ray imaging, the temporal evaluation of keyhole geometry and surrounding melt pool could be observed. The correlation of the results enabled a much deeper understanding of the relevant effects impacting hump formation due to melt-vapour interaction.