You mention monsoon season in Southeast Asia in August. In fact, it's not actually monsoon season all over the region. August falls during the southwest monsoon season, which, in general terms affects the Philippines and Thailand's west coast, but not Malaysia nor Indonesia, which are more affected by the northeast monsoon the opposite time of year.
The best time of year to dive in Malaysia is from March to October, and in most areas of Indonesia the date range is similar (perhaps May to December in some areas).
Having said that, it is sometimes possible to dive even during monsoon season, if you are not going long distances on boats (such as on a liveaboard). This is certainly the case here Phuket, on Thailand's west coast.