A new version of the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (PSU-NCAR-MM5) is introduced. The model employs a mercator projection domain centered at the equator and the north-south boundaries can be moved according to user's need. The east-west boundary merge at a longitude with a small overlap, thereby eliminating the need for a lateral boundary condition in zonal direction. Thus, the model requires only initial conditions and lateral boundary conditions in north-south direction to run. The model tests show no distortion of the model outputs at the overlapping longitude. This new version of MM5 is different from other global models, and can be utilized to cover scales from planetary waves to few kilometers topographic features and clouds in the tropics. Thus, such a model will not only allow to investigate problems in medium-range predictability, but also the general circulation dynamics and the interactions between different components of the tropical atmosphere, which would not be possible using a regional model. The dynamics and physics packages are same as those of regular regional MM5 with nesting capabilities. The initial model runs show its ability to capture the large-scale variability of the tropical atmosphere compared to the observed data sets.