Rains are abundant and intense in tropical monsoon areas. But there is a distinct dry season, though very short. However, the amount of precipitation during the rainy season is so heavy that it more than gives back the absence of rainfall for a few months. Soils retain moisture to support the plant cover. In the tropical monsoon climate summer is generally the rainy season. During the high-sun period the on-shore winds bring a lot of moisture from over the tropical warm oceans to the land. Wherever these moisture-laden winds are forced to rise, abundant precipitation results. However, the coastal regions, if backed by highlands, receive the maximum amount of precipitation. It is important that the leeward sides of the coastal ranges suffer from the rain shadow effects. During the winter monsoon period, January and February are the driest months in South-east Asia. The distribution of rainfall in the subcontinent is more uneven than elsewhere. The rainfall decreases from east to west and from north to south in so much so that the western and north-western regions have almost semi-arid climate.
The monsoon circulation in South-east Asia is characteristically governed by the migration of ITC. Because of differential heating of the continent and the adjoining oceans, there is a complete reversal of pressure gradient over the huge landmass of South-east Asia. During winter there are centers of high pressure over the continent so that there is a flow of air towards the oceanic low pressure centers. These winds are termed 'the winter monsoon' in the eastern and southern Asia. In summer, the huge landmass of Asia develops low pressure centers. These centers are reinforced by the ITC which moves suddenly to the north into the Indian subcontinent. Under these conditions the sea-to-land pressure gradients are established resulting in on-shore winds in eastern and southern Asia. These winds pick up huge quantities of moisture from the warm tropical oceans. Thus, the summer monsoons blowing from southwest Asia and eastern Asia are capable of giving heavy rains wherever conditions are favourable. As the winter approaches, the low-pressure centers are gradually replaced by the high pressure systems.
The change in precipitation is what gives this climate type its name. Precipitation only falls during the summer months, usually from May-August with June and July having the heaviest rain. The whole dry season usually has less than 4 inches of rain. During the wet season, at least 25 inches will fall. Some areas of Tropical Wet and Dry in the path of monsoon winds can receive incredible amounts of rain due to seasonal winds called monsoon. Seasonality of its precipitation is the hallmark and most well-known characteristic of the monsoon climate. Though the annual amount of precipitation is quite similar to that of the rain forest, monsoon precipitation is concentrated into the high-sun season. Maritime equatorial and maritime tropical air masses travel from the ocean on to land during the summer, where they are uplifted by either convection or convergence of air to induce condensation.
The low-sun season is characterized by a short...