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.