We present our recently undergoing work to design and develop a GPU based unified modeling system for seamless weather and climate predictions of Monsoons. The system design is capable of handling different time and spatial scales of atmospheric phenomena that are crucial for accurate forecasting of weather and regional climates, and of monsoons in particular. Our focus is on high-resolution model utilizing accurate approximations on the icosahedral-hexagonal grid. We also develop parameterizations of fine and multi-scale moist convective processes, cloud microphysics and precipitation, radiative transfer, hydrology and land surface processes, atmospheric and oceanic turbulence. Starting with the core of LMDZ model, we are developing from scratch a parallel version appropriate for efficient computation on GPUs and CPUs. Another goal of our system design is to rid the programmer with low level programming details using a programming model that automatically distributes computation among all available CPUs and GPUs appropriately. We are developing a programming API to unify parallel code development on CPUs and GPUs.