Tropical cyclone scales barometric pressure is low compared with its surroundings. Other classifications historically used include: cyclonic storm where the winds did not exceed force 10 on the Beaufort scale and a Cyclone where the winds are either force 11 and 12 on the Beaufort scale. Between 1924 and 1988, tropical cyclones were classified into four categories: depression, deep depression, cyclonic storms and severe cyclonic storms. However, a change was made during 1988 to introduce the category "severe cyclonic storm with core of hurricane winds" for tropical cyclones, with wind speeds of more than . During 1999 the categories Very Severe Cyclonic Storm
Wind wave this point. This relation shows the wind flow transferring its kinetic energy to the water surface at their interface. Assumptions: Generally these wave formation mechanisms occur together on the water surface and eventually produce fully developed waves. For example, if we assume a flat sea surface (Beaufort state 0), and a sudden wind flow blows steadily across the sea surface, the physical wave generation process follows the sequence: Three different types of wind waves develop over time: Ripples appear on smooth water when the wind blows, but will die quickly if the wind stops. The restoring force that allows them