The May to November winter season is when to go to Mozambique for cooler temperatures and the least chance of rain; December to April is the wet summer season although it generally rains in brief but vigorous downpours after which the sun comes out again. Note that January and February is cyclone season in southern Mozambique and there's every chance of a great deal of torrential rain - we'd advise avoiding the Bazaruto Archipelago at this time.