The formation of a cyclone depends on the speed and direction of the wind, temperature and humidity. Humidity is the amount of water vapour in the atmosphere. As the humidity in a region increases, the difference in temperature also increases. A cyclone arises due to the difference in the temperatures between two regions. A low pressure is created as the air in the high temperature region becomes warm and rises. The gap in the low pressure area is filled by cold air rushing in from the surrounding areas. When the warm air rises, it cools, condenses and forms clouds. When the water vapour in the clouds turns into rain drops, the heat possessed by the water vapour is released into the atmosphere. The process repeats and the release of heat from the water vapour continues. Falling water droplets and rising air move vigourously to produce thunderstorm, which develops into a cyclone under certain weather conditions. The calm and clear area at the centre of a cyclone is called the eye of the cyclone.