We investigate the problem of beamformer design for communications systems coexisting with legacy radar systems with mechanically rotating antennas. Based on measurement campaign findings that support the assumption of fast decoherence for the radar-to-base station interference within a radar rotation, as well as the assumption of very strong correlation of interference channel realizations corresponding to the same radar rotation phase, we introduce beamforming solutions exploring these channel characteristics, without imposing the need for current channel state information. Different beamformer designs are proposed, characterized by different levels of computational complexity, that are applicable both in the case of synchronous systems, where the communication system is aware of the radar rotation phase, as well as in the case of asynchronous systems.