The climate of the Quirimbas (or Fortunate) Islands, an archipelago in the north of Mozambique, is tropical, hot all year round, with a hotter, more humid and rainy season from December to April, in which the maximum temperature hovers around 31/32 °C (88/90 °F), and a dry season from May to November, which includes a cooler period from June to August. In this relatively cool period, the southeast trade winds prevail, blowing steadily from the sea, while the warmest period is dominated by hot and moist air masses coming from the interior of Africa.
Here are the average temperatures (recorded in the nearby town of Pemba, on the coast of Mozambique).
Average temperatures - Quirimbas

Quirimbas	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Quirimbas	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	24	24	23	23	21	19	19	20	20	22	23	24
Max (°C)	31	32	31	31	30	29	28	29	30	31	31	32
Min (°F)	75	75	73	73	70	66	66	68	68	72	73	75
Max (°F)	88	90	88	88	86	84	82	84	86	88	88	90

In the Quirimbas, where unspoiled nature rules, we can find many land and marine species of great interest, such as dugongs, dolphins, sea turtles, whales, sharks, in addition to the reef. The main islands are Metundo, Vamizi, Matemo, Sencar, Mefunvo, Quisiva, Ibo, Medjumbe, Quirimba, Rolas, and Quilaluia.

Rainfall is not particularly abundant, given that it amounts to about 850 millimetres (34 inches) per year; however, it exceeds 100 mm (4 in) per month from December to April, with a peak in March of even 200 mm (8 in), while it becomes scarce from May to November, when there are rare showers, most likely in May and November, that is, the beginning and the end of the dry season.
Here is the average precipitation.
Average precipitation - Quirimbas

Quirimbas	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Quirimbas	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	145	155	200	120	30	15	10	8	2	10	40	125	860
Prec. (in)	5.7	6.1	7.9	4.7	1.2	0.6	0.4	0.3	0.1	0.4	1.6	4.9	33.9
Days	11	10	13	9	3	2	2	1	1	1	4	8	65

From November to mid-May, the archipelago can be affected by the tropical cyclones of the South-West Indian Ocean, although they are more likely from January to March.



The amount of sunshine in the Quirimbas is good from May to November, and especially at the end of the dry season, from September to November, but all in all it's acceptable also in the wettest months, which reflects the fact that the rains come in the form of downpour or thunderstorm, which do not last long and soon give way to the sun.
Sunshine - Quirimbas

Quirimbas	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Quirimbas	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	6	6	6	7	8	8	7	8	9	9	9	8

For swimming, the sea is warm all year round: the water temperature ranges from 25 °C (77 °F) in August, to 29 °C (84 °F) in the period from January to April.
Here are the average sea temperatures.
Sea temperature - Quirimbas

Quirimbas	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Quirimbas	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	29	29	29	29	28	27	26	25	26	27	28	28
Sea (°F)	84	84	84	84	82	81	79	77	79	81	82	82

The best time to go to the Quirimbas runs from mid-May to October. Usually the weather is good also in the first half of May and in November, but there is a risk, albeit not high, of the passage of a tropical cyclone. From mid-May to August, you can bring a sweatshirt for cooler evenings.