An examination of damage to the under-side of the North Rankin 'A' gas platform following tropical cyclone Orson in April 1989 indicated that waves of more than 20 metres had battered the base of the rig. Short period wind gusts are often 40 per cent or more higher than the average wind speed. The circular eye of a tropical cyclone is an area characterised by light winds and often by clear skies. The eye is surrounded by a dense ring of cloud known as the eye wall which is the area of heaviest winds and seas. Following the passage of the eye the winds shift to the opposite direction with equal force.
Tropical cyclones vary in both size and intensity.
Both large and small cyclones can have equally devastating wind speeds near the centre. Radar and satellite images often show that the eye wall clouds are the innermost coil of a series of spiral rain-band clouds. These bands may extend up to 300 nm from the eye wall and are often associated with thunderstorms and very strong wind squalls. For example 25.4 South is the latitude of twenty five decimal four degrees south, not twenty five degrees four minutes south. These are issued whenever a tropical cyclone or developing weather situation is likely to cause strong winds, gales, storm or hurricane-force winds.