Urban Heat Island Effect (UHI) is one of the most evident anthropogenic interventions on climate. During the last 20 years, a lot of research on monitoring and simulation of UHI was done by different institution across the world. However, there are some aspects not very clarified, for example, the decoupling and quantification of the different factors influencing UHI, depending on the location. In this paper, the Urban Weather Generator tool (UWG) is used to test the influence of some factors (density, vertical growth, loss of green, electricity and cars) on the resulting summer time UHI intensity in cities of the Pacific Latin-American coast.