In the 24-hour period beginning 2300 UTC on August 4, 1986, an intense east coast cyclone produced 328 mm of rain in Sydney, Australia, causing widespread flooding. The operational quantitative precipitation forecast, based on 150-km resolution, was poor, predicting only 16 mm of rain. In this study, numerical simulations of this event are carried out after modifying the large-scale and cumulus convection precipitation mechanisms. These changes make the mechanisms mutually exclusive at a given time and grid point, and more sensitive to orographic forcing and surface energy fluxes. Marked improvement in the amounts of predicted rainfall occurs as the horizontal resolution of the model increases. These results indicate that mesoscale processes play an important role in determining rainfall amounts associated with east coast cyclones and demonstrate the potential to accurately simulate very heavy rainfall events. ¿ American Geophysical Union 1990