How big are tropical cyclones?
The size of a cyclone is usually described in terms of the radius of gale-force (sustained winds of at least 63 km/h). Although the distribution of surface winds is never completely symmetrical estimates of the gale-radius provide a reasonable guide on the size of a system. Cyclones off the northwest have an average radius of gales of about 150 to 200 kilometres. It is common for gales to occur well beyond the average radius of gales in one quadrant, for example the northwesterly monsoon winds to the north of the centre. The size varies considerably. The radius of gales of Rosita (Broome, 2000) was just 70 km compared to the 350-400 km of Orson (1989). The adjacent picture shows the 100 km diameter of gales of Tracy (Darwin, 1974) could fit into the eye of Kerry (Qld, 1979) which had an eye diameter of 180 km. The areal extent of gales is also very important for wave generation and rainfall. The radius of storm-force (sustained winds of at least 90 km/h) and hurricane-force (sustained
