Coordination for dynamic task allocation based on available resources is a very challenging research issue in disaster environments with time, space and communication constraints. In addition, the space and communication constraints and the dynamic features of disaster environments make an extra difficulty to achieve efficient coordination through centralised coordination approaches, which require the coordinators to have global knowledge of the environments. To this end, a coordination approach for dynamic weighted task allocation is proposed in this paper. The proposed approach considers time, space and communication constraints in disaster environments and urgent degrees of workloads of tasks without requiring the global knowledge of the environment. In particular, a dynamic group formation mechanism is developed to help agents to form groups and share information for task allocation under space and communication constraints in a decentralised manner, which can reflect real-life situations in disaster environments. The efficient coordination for task allocation is achieved through the utility calculation within each group. The experimental results show that the proposed approach outperforms most of other coordination approaches, such as the group formation approach proposed by Glinton et al. and the heuristics task allocation approach proposed by Ramchurn et al. in terms of group formation and weighted task allocation in disaster environments with time, space and communication constraints.