The year in the archipelago
The figures are those of Zanzibar City. Temperature barely moves — the annual mean is 26.9 degrees — so here the calendar is written by the rain.
There is a photograph of Zanzibar that circulates a lot and that nobody explains: an endless beach of rippled sand, the water so far away you cannot see it, and a row of boats sitting on the bottom. It is not an odd day or a bad beach. It is low tide, and it happens twice a day, every day of the year.
Almost every guide devotes its when-to-go section exclusively to rain. That information is correct and necessary, but incomplete: it tells you which month to book and nothing about what time of day you will be able to get into the water.
01 Two rainy seasons, not one
Here temperature is barely a variable. The annual mean is 26.9 degrees and the coolest month, August, has a daily mean of 25.2. Between the hottest month and the mildest there is little more than three degrees. What does change, enormously, is how much water falls.
The year has two separate wet seasons. The long one runs from March to May and peaks in April, with 408.5 millimetres over 17.5 days with rain: more than a quarter of the annual total, 1,649.5 millimetres, falls in that single month.
The short one arrives in November and December, with 201.3 and 167.7 millimetres. It is less brutal, falls more concentrated and does not usually ruin a whole trip, but it coincides with the most expensive stretch of the calendar.
And between the two lies a spectacular dry block. From June to September rain stays between 30.8 and 51.9 millimetres a month, with July the absolute minimum. They are also the coolest months: August has average lows of 21.1 degrees, which makes the nights very manageable.
How the year divides up
Between 30.8 and 51.9 millimetres a month and the year's lowest temperatures: highs of 29 degrees and lows dropping to 21.1 in August. It is the most reliable window and also the windiest, which helps with the heat and complicates calm water.
February is the driest month of the year's first half, with 50.8 millimetres over just 3.6 days with rain, and the hottest, with average highs of 33.2 degrees. Flatter sea and less wind, but the heat is real and the coast is busy.
408.5 millimetres in April and 297.8 in May, over 17.5 and 13.8 days with rain. It is the only stretch of the year that can genuinely spoil a beach holiday. In exchange, it is when the island is greenest and cheapest.
October still holds up with 115.7 millimetres concentrated in 6.9 days, but November climbs to 201.3 over 13.7 days. December usually improves in its second half, exactly when prices peak.
02 The table that actually matters
And now the part that almost never appears. The tide rises twice every twenty-four hours, and along much of the coast the difference between high and low water transforms the landscape. At high tide you have a turquoise lagoon; at low tide you have a sand flat.
It is not a minor detail. In villages on the northeast coast, checking tide timetables before going to the beach is explicitly recommended. And it is not only a matter for swimmers: on the northern island, the tides decide what time a dhow can enter the harbour.
The practical conclusion is that here you plan the day the way you plan it in a port, not the way you would at a Mediterranean resort. The water hours shift daily, so swimming, boat trips and diving are fitted around the table, not the other way round.
03 The coast you choose changes the problem
Not all coasts behave the same, and this is decided when you book accommodation, not when you arrive. On the east and southeast coasts there is a shallow, sandy-bottomed lagoon sheltered by an offshore reef, and it is exactly that lagoon which empties.
The flip side is that this same lagoon, shallow and waveless, is an excellent place to learn sailing and kite sports, because the reef stops the swell and the wind comes in consistently for much of the year.
If what you want is to swim at any hour without checking any table, the answer lies in the north of the larger island and on coasts where the bottom drops away sooner. It is worth asking explicitly before booking: it is the one question that genuinely changes the trip.
04 The wind and what it brings
There is a third variable, and it is the oldest of all. In this stretch of the Indian Ocean the wind changes direction with the seasons, and that reversal was for centuries the timetable of maritime trade: traders arriving by sea stayed on the coast for up to six months waiting for the wind to turn.
For today's trip that translates into a simple rule: the dry block from June to September is also the windiest, and that cuts both ways. It cools the nights and is a gift for anyone sailing or kiting, but it stirs up the water and complicates calm diving.
05 The months nobody recommends and that sometimes work
October is the calendar's underrated month. Its 115.7 millimetres look like a lot compared with July, but they fall over just 6.9 days: concentrated rain, not persistent. In exchange the sea is flatter than in the middle of the dry block and December prices have not arrived.
And an honest warning about April and May. With 408.5 and 297.8 millimetres there is no way to sell those months as good for the beach. But it is when the island is green, when prices fall and when you see the archipelago without the tourist layer on top. It is a different trip, not a worse one.
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