Recent studies have proven the need for realistic urban representation in weather models. However, cities modeled using distributed urban parameters with updated urban parameterization are still few and limited to highly developed countries. Furthermore, real building datasets used to estimate the urban parameters are unavailable or lacking in other cities. This study was conducted to address both issues by expanding the advance weather model methodology to another megacity and utilizing global datasets to readily estimate a distribution of urban and other surface parameters. Sensitivity of the models to either real or global-estimated urban parameters was conducted; and the urban effect to a synoptic circulation over Istanbul was investigated. The simulation results for a typical summer day over Istanbul suggest that global datasets can be used as alternative to real building data for estimating distributed urban parameters.