Rainfall associated with tropical cyclones in the northeast Australian region

Spatial and temporal distributions of rainfall in tropical cyclones which are wholly located over the Coral Sea are studied from forty years of records at Willis Island (16.3°s, 150.0°E), a small coral island of low relief. By relating the distance and bearing of Willis Island from the cyclone centre to the direction of cyclone movement and plotting twenty-four hour rainfall data on polar diagrams, an envelope of the heaviest rain area is obtained, both for eastward and westward moving cyclones. Rainfall patterns over the mainland are examined in detail for twenty well-documented cyclones which have had a minimum path of 200 miles over the Australian continent, chiefly in Queensland and New South Wales. The a real distribution of the rain is discussed with reference to the various types of cyclone tracks and quantitative estimate of mean rainfall depths are derived from area-depth curves based on isohyetal maps. The variation in such depths from cyclone to cyclone is studied in relation to the speed, size and intensity of the cyclone, as well as the moisture content of the inflowing air and the mean elevation of the topography in the rain area. To determine the effect on the rainfall of the filling process in each cyclone as it moves inland, mean rainfall depths are related to changes in central pressure during the corresponding twenty-four hour periods.