Depends where you plan on diving, August is pretty good for Raggie sightings off Aliwal shoal (Durban) and the sea conditions are fine. Its unlikely you will find a number of shark species in one area, so for Ragged tooth sharks, and probably Sand sharks August is good off Aliwal Shoal, Protea banks may have a tiger sighting, but you are more likely to see Zambezi's, Black Tips or perhaps a Hammerhead or two.
Further North like Sodwana Bay the conditions should be good, but shark sightings off the usually dived reefs (Two Mile) are not really common, Ragged Tooth sharks are seen in certain areas at specific times but you would need to go further out like to 5 mile or even 9 mile reef when you stand a better chance of seeing bigger predators, mostly black tip sharks or Hammerheads.
Great Whites are almost never seen in these waters, I have been diving here for over 35 years and never seen a Great White further North than Gansbaai in the Western Cape. Cape Town has a myriad of Great white diving adventures, most dont even use Scuba, so anyone can do it.