Thailand is divided into three seasons. The first is the rainy or southwest monsoon season (mid–May to mid–October), which is caused by southwestern wind from Indian Ocean. Rainfall is also contributed by Intertropical Convergence Zone (ITCZ) and tropical cyclones. August and September being the wettest period of the year. The country receives a mean annual rainfall of . Winter or the northeast monsoon occurs from mid–October until mid–February. Most of Thailand experiences dry weather with mild temperatures. Summer or the pre–monsoon season runs from mid–February until mid–May. Due to its inland nature and latitude, the north, northeast, central and eastern parts of Thailand experience a long period of warm weather, where temperatures can reach up to  during March to May, in contrast to close to or below  in some areas in winter. Southern Thailand is characterised by mild weather year-round with less diurnal and seasonal variations in temperatures due to maritime influences. It receives abundant rainfall, particularly during October to November.