Monsoon stages, illustration. This sequence starts at upper left, with the Sun heating a coastal mountain range. Hot air rises from above the mountains, drawing in cooler air from the sea (arrows at upper right). The moisture-laden air forms precipitation (rain) over the mountains as it cools (centre left). This is the summer monsoon cycle. In the winter, this process reverses, with the land cooling faster than the oceans (centre right). Warm air over the land flows downwards and outwards (arrows at lower left), which can result in further heavy rainfall if this mass of moving air reaches land (lower right). Summer monsoons tend to be westerly, while winter monsoons tend to be easterly.