Cyclones are large revolving tropical storms caused by winds blowing around a central area of low atmospheric pressure. In the Southern Hemisphere, these tropical storms are called cyclones and rotate in a clockwise direction, while in the Northern Hemisphere cyclones are called hurricanes or typhoons and rotate in a counter-clockwise direction.

Cyclones develop over warm waters in the tropical regions of the oceans, where areas of very low pressure are created by air being heated by the sun. This causes the air to rise very rapidly and become saturated with moisture that condenses into large thunderclouds.

Cool air rushes in to fill the void and is bent inward and spirals upward with a great force caused by the coriolis effect of the earth spinning on its axis. Because of this, the winds begin to rotate faster and form a large rotating weather system, in some cases up to several thousand kilometers in diameter. In the center of this system there usually is a cloudless, calm area called the eye, with no rain and very light winds.

The cyclone is sustained by a steady flow of warm, moist air being sucked in from the warm waters over which t is moving. A wall of towering clouds forms around the eye of the cyclone, and it is here where the heaviest rains and strongest winds are recorded.

Source: Australian Institute of Marine Science