I dove from a land based operation on Zanzibar two years ago after finishing a safari trip in Tanzania. It was near the end of February. Before I left L.A. I had contacted the dive operation (One Ocean, The Zanzibar Dive Center) and made arrangements for 3 days of two tank dives.
The first day there was myself and a couple from Germany and three snorkelers. It was windy with 4 ft waves getting over the reef (in a small skiff) and then an hour or so to Pemba Island. With the windy conditions the visibility wasn't all that great. Maybe 25ft but I did find a few critters to photograph.
The next day the owner of the dive operation told me that the diving that day had been canceled "due to weather conditions" and said the same thing on the third day. I think he just didn't have enough divers to make it worth his while.
Then the guy had the gall to try to charge me for all 6 dives! I told him no bleepin' way! Then he said he would only charge me half. I again told him no. I would only pay 1/3 of the charge. I got 2 of the 6 dives and that's all I would pay for. He said he was going to charge my credit card for half of the amount. Since I hadn't signed anything yet I told him fine, I'd just dispute the entire charge! He immediately got religion!! And to be a good sport about it I bought a couple of overpriced T-shirts from him!
Still, I was really put out having to drag my dive gear and underwater camera with strobes all over East Africa to only get two dives!!
I've met several divers who've dove off the coast of Mozambique that say the diving is very good!
Let me know how it works out for you. firstname.lastname@example.org