Previous studies have shown that terminal velocity raindrops striking a smooth water surface create oscillating bubbles that radiate significant underwater sound energy. Those studies identified two diameter ranges that produce bubbles: small drops (.8-1.1 mm diameter) which produce bubbles by one mechanism and large drops (2.2-4.6 mm diameter) which create bubbles by a different mechanism. Effects of oblique incidence have been studied only for small drops. Average energy spectra were calculated for a range of raindrop sizes striking a smooth water surface. This work deals with the real life situation of large raindrops of a size often present in heavy rainfall (4.6 mm diameter) striking a sloped water surface. Terminal velocity is used to simulate natural rainfall, and the sloped surface is used to simulate the surface gravity waves of a natural sea. The effects of a sloped water surface on frequency spectra and energy for 4.6 mm raindrops are estimated. By comparing energy spectra generated by single drops in an anechoic laboratory tank to underwater sound spectra measured at sea, it will be possible to estimate heavy rainfall rate by means of remote underwater listening devices.... Spectral energy density, Primary bubbles, Type I and Type II mechanisms, Aerosols, Time gap.