To a certain degree, wearing sunglasses in a heavy rain can help you increase your visibility. I know you will think it is strange and at first I think so, however, now I believe it, because I have experienced the fact. As you know, when we are in the rain, the sunglasses will ease the distraction of raindrops hitting your eyes then glare is not much an issue during a rainy day, so we can see clearly in the rain (including the heavy rain). I am a girl with glasses; nevertheless, I would like to wear my sunglasses in rainy day, which can help me enjoy the light and clearness of the world. Of course, there is some trouble if you do so, for example, you will have to clear up your lens from time to time as rain will build up on the lens, and visibility will be reduced.