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Rainfall time distribution hyetograph of the design storm is highly needed to run hydrological models. This paper derives a dimensionless rainfall time distribution from observed storms based on the SCS TP149 procedure of re-arranging the storm pattern so that the greatest depth values occurs at the middle of the total duration. One hundred twenty-seven rainfall storms for Sinai area were categorized into four groups according to the total duration. Finally, the cumulative design distribution curves are calculated and renamed WRRI distribution. The developed synthetic rainfall distribution curves were compared to the most common distributions such as the standard 4 Soil Conservation Service (SCS) profiles. The performance of the developed rainfall pattern is evaluated using real cases. There was a significant difference in computing runoff between the proposed WRRI and SCS distributions. The research recommends using the developed curves to create storm hyetograph of any design storm for Sinai. Keywords: Rainfall hyetograph, Dimensionless time distribution, Runoff estimation, Sinai