Guanajuato lies 6,558 feet above sea level in Mexico’s central highlands. Therefore, the city has a mostly warm and mild climate, May being the hottest month of the year and December and January the coldest months.
During June, July, August, and September it is Guanajuato’s rainy season, and the summer temperatures are cooled by the rain. Note that the rain can be very heavy, so you should definitely bring some kind of protection, though nothing too bulky, as it is also summer.
Due to these climate conditions, most houses don’t have heating or air conditioning systems installed.