First Time In Japan and I am Concerned About the Weather and Rain

I am planning to visit Osaka (3 days) Kyoto (3 days) and Tokyo (8 days) and the forecast shows that almost half of the days I am visiting are rainy with 30%. For people who visited Japan in summer, is the rain so harsh that I won’t be able to walk outside and sightsee or is it not that big of a problem?