The East coast of Zanzibar has a fringing coral reef that runs parallel to the East coast from the Southern most tip right up the coast to the Northern most tip of the island.
During the Months of May through to October, Zanzibar gets the large southern swells that push up from South Africa.
The reef just off Nungwi has the best breaks with two super waves, one being a peak and the other being a fast right hander. The best times of the day to Surf are two hours either side of the low tides.
The swell can varry from 3ft to 8ft on big days. The wind blows off shore in the morning and then side shore in the afternoons.
Your best bet is to be around during the low spring tides in the morning that generally last for 7 days.