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Meteorological Aspects of an Extraordinary Flash Flood Event Near Dapto, New South Wales

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.

Additional Information

Field Value
Title Meteorological Aspects of an Extraordinary Flash Flood Event Near Dapto, New South Wales
Publication Date 1 May 1985
Themes Land and Resource Management
Spatial Extent
Map data © OpenStreetMap contributors
Council/LGA Wollongong City Council
Author/ Prepared by Shepherd D.J. and Colquhoun R. Regional Office Bureau of Meteorology Sydney
Publish date 4 June 2020
Update date 4 June 2020
Approval State Approved
Submitted for approval 4 June 2020
Submitted by Julia Muniz de Miranda Sa
Approved 4 June 2020
Approved by dstazic
Identifier cc3c9210-c9d4-498c-be11-6cd969052af5