In Guinea Bissau, the climate is tropical, hot all year round, with a dry season from November to May, and a rainy season from June to October, due to the African monsoon. The hottest period runs from February to May, before the rains, while the rainy season, though less hot, it's muggy. The heat is intense especially in the interior, while along the coast, where the capital Bissau is located, it's a bit cooler because of the breeze.
Here are the average temperatures in Bissau.
Average temperatures - Bissau

Bissau	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Bissau	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	19	20	22	23	24	24	23	23	23	23	23	21
Max (°C)	31	32	33	33	32	31	29	28	29	31	31	31
Min (°F)	66	68	72	73	75	75	73	73	73	73	73	70
Max (°F)	88	90	91	91	90	88	84	82	84	88	88	88

The monsoon rains are very heavy, especially from July to September, when they can cause widespread flooding. In addition, in this period the sky is often cloudy. August is the rainiest month, and if possible it should be avoided. The rainfall is more abundant in the south, where it exceeds 2,000 millimetres (79 inches) per year, and less abundant in the north, where it amounts to around 1,500 mm (60 in) per year.
In Bissau, precipitation amounts to 2,000 millimetres (79 inches) per year. Here is the average precipitation.
Average precipitation - Bissau

Bissau	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Bissau	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	1	1	0	1	17	175	470	680	435	195	40	2	2017
Prec.(in)	0	0	0	0	0.7	6.9	18.5	26.8	17.1	7.7	1.6	0.1	79.4
Days	0	0	0	0	2	11	22	24	21	13	2	0	95

In Bissau the sun often shines from November to May, while in the rainy season the sky is often cloudy, especially in the wettest period, from July to September.
Sunshine - Bissau

Bissau	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Bissau	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	8	8	9	9	9	6	4	3	5	7	8	8

During winter, the weather is sunny, and the air is dry because of the prevailing wind, the Harmattan, which blows from the desert, and can bring dust, making the sky whitish. Normally the daytime temperature is about 30 °C (86 °F), but sometimes it can touch 40 °C (104 °F). However, this is the best time of the year. Starting from February, both temperature and humidity gradually increase, reaching a peak between March and May, when it can easily surpass 40 °C (104 °F). Starting from June, the rains lower the temperature to about 28/30 °C (82/86 °F), but moisture makes the heat muggy. However, at least on the coast the heat is tempered by the breeze.
Here are the average temperatures of Gabù, located in the north-east, where the heat is intense in the months preceding the monsoon.
Average temperatures - Gabù

Gabù	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Gabù	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	16	19	21	23	24	23	22	22	22	22	20	16
Max (°C)	32	35	37	38	37	33	30	29	30	32	33	31
Min (°F)	61	66	70	73	75	73	72	72	72	72	68	61
Max (°F)	90	95	99	100	99	91	86	84	86	90	91	88

In Gabù, 1,400 mm (56 in) of rain per year fall.
Average precipitation - Gabù

Gabù	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Gabù	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	0	0	0	3	40	155	275	400	345	185	25	2	1426
Prec.(in)	0	0	0	0.1	1.6	6.1	10.8	15.7	13.6	7.3	1	0.1	56.1
Days	0	0	0	1	4	10	17	20	17	9	2	0	80

In addition to being less rainy than the coast, the north-east is also more sunny.
Sunshine - Gabù

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

The sea is always warm enough for swimming, although it is warmer from June to November, when the water temperature is about 28 °C (82 °F), while in March and April it becomes almost cool, since it goes down to 23 °C (73 °F).
Sea temperature - Bissau

Bissau	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Bissau	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	25	24	23	23	26	28	28	28	28	28	28	27
Sea (°F)	77	75	73	73	79	82	82	82	82	82	82	81

The best time to visit Guinea Bissau is winter, in particular the months of December and January, which are the least hot, among those in which it does not rain. It may be useful to bring a scarf, for the dust brought by the wind. For a beach holiday, the dry season, from November to May, is preferable.


In winter: in Bissau and the coast, light clothes for the day, a sweatshirt for the evening, a scarf for the wind-borne sand and dust. In inland areas, you can add a light jacket for the evening.
In summer: light clothing of natural fibres, a light sweatshirt and a light raincoat for the rain.