A computational scheme of the primitive equation model in the pressure coordinate system is presented. The scheme has the conserving properties for the mass and the energy. The pressure changes at the lower boundary are computed by the tendency equation, in which the orographic effects are included.
The formulation of lateral boundary conditions for the telescoping mesh is also presented. The normal flow components at the boundary are determined first by the continuity relation using the solutions inside the smaller area and also the divergence given by the large area solution, and secondly are modified in order to reduce the differences of them from the large area solution. Other variables specified at the boundary are discussed. These treatments do not need artificial smoothing at the boundary.