This paper presents an a posteriori approach to unstructured mesh generation via a localized truncation error analysis and applies it to the western North Atlantic tidal (WNAT) model domain. The WNAT model domain encompasses the Gulf of Mexico, the Caribbean Sea and the North Atlantic Ocean east to the 60°W meridian. In this paper, we focus on the area surrounding the Bahamas. A bathymetric data set with fine resolution is employed in separate linear, harmonic simulations of shallow water tidal flow for seven different tidal-forcing constituents. Each set of simulation results is used to perform a truncation error analysis of a linear, harmonic form of the depth-averaged momentum equations for each of the different tidal-forcing frequencies. The process has been built upon successful research aiming to produce unstructured grids for large-scale domains that can be used in the accurate and efficient modelling of shallow water flow. The methodology described herein can also be transferred to other modelling applications.