Seoul has a humid continental climate influenced by the monsoons (Köppen: ''Dwa''). Being in the extreme East Asia, the climate can be described as humid subtropical with great variation in temperature and precipitation throughout the year. (''Cwa'', by -3 °C isotherm). The suburbs of Seoul are generally cooler than the center of Seoul because of the urban heat island effect. Summers are hot and humid, with the East Asian monsoon taking place from June until September. August, the hottest month, has average high and low temperatures of  with higher temperatures possible. Heat index values can surpass  at the height of summer. 