Winter (June - September): Like mainland Tanzania, the best time to go to Zanzibar, Mafia or Pemba is during the dry season from June to September. Due to its close proximity to the equator, the temperatures vary very little through the year, with maximum daytime temperatures hovering between 25°C / 75°F and 28°C / 82°F throughout the year. The dry season is famous for its clear blue skies and sunny days. This is also the best time to go scuba diving as the water will be crystal clear and visibility will be at its peak. Going in June or beginning of July will have the added bonus of the vegetation being green and lush after the rains. September is usually spice harvest season, and it is quite fascinating to watch the farmers harvest cloves by hand. Winter has the added bonus of combining beautifully with a safari to Ngorongoro Crater, Serengeti and Mount Kilimanjaro.
Summer (January - March): January to March is summer and our second favourite time to visit Zanzibar, Mafia or Pemba. The summer months bring with them beautiful dry, sunny and warm days with bright blue skies very similar to winter, with temperatures averaging around 28°C or 82°F.
Spring (November - December): Spring will bring short rains in the form of late afternoon showers. The rains are intermittent and not too much of a bother, but we do feel that when choosing to go to a beach destination, dry season would be better, making the period of November to December not our top pick.
Autumn (April - May): Autumn is the least desirable tome to visit any of the islands, be it Zanzibar, Mafia or Pemba. April and May are monsoon season with spectacular storms and long rainy days. The waters are rough and murky, and the beaches wet and windswept. Many hotels close altogether during these months to refurbish and upgrade their lodgings for the next season. Luckily these long rains coincide with mainland Tanzania as well, which rules out only these two months, and leaving 10 months for a magical Bush + Beach combination.