mumbai and goa in august - please help

I decided last minute to go on holiday to India. I stupidly didn't think of the monsoon season. I fly into Mumbai 29 July and had thought of travelling down to Goa. Has anyone been to these places at this time of year? How bad does the rain get - all day every day? Or a few hours a day? I'm also now quite nervous about how dangerous it could be with landslides and floods etc.. I had so much been looking forward to this trip. Any advice would be much appreciated. Thank you