You can go to Goa. The rainy season in Goa lasts through August, but by the end of the month, the monsoon is waning. Therefore, August is the best month to visit Goa.
Lonavala is a gorgeous place to visit in the monsoon. A significant advantage of Lonavala and Khandala is the pleasant weather throughout the year.
Mount Abu is also a pleasant place to visit in August. Mount Abu's lush greenery is at its best this time of year.