Tropical cyclones have their birth in the warm parts of the Atlantic, Pacific, and Indian oceans. They move on a curving course. If these disturbances have a very low atmospheric pressure at their centres, they are given such names as hurricane or typhoon.
Tropical cyclones are characterised by the following properties: (1) The isobars are circular and symmetrical. At the centre, the air pressure is extremely low so that the pressure gradient is very steep and the winds are very strong. (2) Rainfall is torrential in nature but is distributed evenly around the centre. (3) The area covered is relatively small, the diameter being only 150 to 500 km. The central part, termed the eye of the storm, has a diameter of only 10 to 50 km.