Extraordinary short-duration heavy rainfall on 18 February 1984 was found to be caused by several meso and synoptic-scale focusing mechanisms. Of particular importance was the formation of a mesoscale low pressure centre which strengthened surface winds to storm force over a very localised area and enhanced convergence mainly in its southeast quadrant. Methods of providing estimates of probable maximum precipitation had to be revised, because maximised rainfalls during the event exceeded available estimates for short durations and small areas by up to twenty nine per cent, Because of the scale of the event, successful forecasts of similar occurrences, by synoptic or numerical methods, are unlikely in the near future. Utilisation of digital radar data, telemetered rain-gauge networks, and nowcasting techniques would appear to be the most promising means.by which a warning service could be provided.

In this paper the spatial and temporal distribution of the rainfall is described. There is an excellent network of pluviographs in the area operated by the New South Wales Public Works Department and the Metropolitan Water Sewerage and Drainage Board which enables temporal patterns to be precisely defined. Wollongong University Geography Department collected all available rainfall data from private gauges and these have been included in the isohyetal analysis. Observations from a 10 cm wavelength and 3 degree beamwidth radar are discussed and three-hourly satellite data are used to determine what process was responsible for the heavy rainfall. The broadscale meteorological situation is described as is the mesoscale wind flow in the storm area. The mesoscale analysis was made possible by a network of anemographs established by Macquarie University in the Wollongong area. The discussion section looks at the focusing mechanisms responsible for the heavy rainfall, the efficiency of the storm, the implications of the storm for short-duration probable maximum precipitation studies, and the forecasting of heavy rainfall events.