In the Republic of Congo, an African country crossed by the Equator, the climate is equatorial (hot and humid all year round, with no dry season) in the north, and tropical (hot and humid, with a dry and a rainy season) in the center and south.
In the north (see Ouésso, Impfondo), temperatures are stable during the year, however, they slightly decrease in July and August. Here are the average temperatures of Ouésso, located in the north, at 350 metres (1,150 ft) of altitude.
Ouesso - Average temperatures
Min (°C)202021212121212121212120
Max (°C)313232323130292930303030
Min (°F)686870707070707070707068
Max (°F)889090908886848486868686

However, in the north there are two rainier periods due to the zenith passages of the sun (that is, when it shines directly overhead in the sky at mid-day), and two relatively dry periods, December to February and June to August. In addition, the more we go to the north, the more evident is the first dry period (the one that goes from December to February) because we are moving away from the equator and entering the area where the rainfall regime is typical of the Northern Hemisphere (ie with a dry winter). The result is that the rainfall in the north is better distributed, so the area is covered by the forest, while the central and southern areas are covered by savanna.
Here is the average precipitation in Ouesso.
Ouesso - Average precipitation

In the north the sun does not shine very often; however, it can be seen a little more often in the hotter period, from January to May, and less often in the cooler period, in July and August.
Ouesso - Sunshine

In the centre and south, in the tropical region, the dry season, which corresponds to the winter of the southern hemisphere, runs from June to August in the centre, from June to September in the south, and from mid-May to mid-October on the coast. The amount of rainfall ranges from 1,500 to 2,000 millimetres (60 to 79 inches) per year in the north, while in the south it decreases towards the coast (see Pointe Noire), where it descends to 1,200 mm (47 in).
Here is the average precipitation in Pointe Noire.
Pointe Noire - Average precipitation

In fact, in the winter months the sea is cooled by the cold Benguela Current, which almost completely inhibits raincloud formation for a longer period than elsewhere in the country; on the other hand, this current generates fogs and low clouds, which reduce sunshine. Here are the sunshine hours at Pointe Noire.
Pointe Noire - Sunshine

In inland areas, temperatures are high throughout the year, and the air is hot and muggy: the daily average ranges from 25 °C (77 °F) in January, to 26 °C (79 °F) in February and March, to 24 °C (75 °F) in July and August, while nights can be a bit cool from June to August in the hills of the Plateaux Department, around 16/17 °C (61/63 °F).
On the coast, the temperature becomes a little cool during the day from June to September, when highs hover around 25 °C (77 °F), however, because of the mitigating effect of the sea, at night it remains quite high, around 18/20 °C (64/68 °F), as we can see from the averages of Pointe Noire.
Pointe Noire - Average temperatures
Min (°C)242424242320181921232324
Max (°C)303031302927252526282929
Min (°F)757575757368646670737375
Max (°F)868688868481777779828484

In the capital, Brazzaville, which is situated at 320 metres (1,050 feet) above sea level, in the south-east, along the Congo River, which gives its name to the country, daytime temperatures are about 30 °C (86 °F) from September to January, they go up to 31/32 °C (88/90 °F) from February to April, and then they drop to around 27/28 °C (81/82 °F) from June to August. Here are the average temperatures.
Brazzaville - Average temperatures
Min (°C)212122222118171820212121
Max (°C)303131323028272830303029
Min (°F)707072727064636468707070
Max (°F)868888908682818286868684

In Brazzaville too, the sun does not shine very often, and there is not even a big difference between the different periods of the year; however, the sunniest months are March and April, while the least sunny are July and August.
Brazzaville - Sunshine

In Brazzaville, rainfall amounts to 1,350 mm (53 in) per year, with two maxima in Aprile and November, while it hardly ever rains from June to September. Here is the average precipitation.
Brazzaville - Average precipitation

North of Brazzaville, on the Koukouya Plateau, it rains more than in the capital, around 1,800/2,000 mm (70/80 in) per year, with two maxima in March-April and October-November.
As previously mentioned, the amount of sunshine is not excellent throughout Congo, and it does not get better in the cooler and drier season, on the contrary it slightly worsens, when even in the interior the sky is often cloudy, while in the period from October to April, between the rain showers the sun comes out.

Congo, elephants

The sea is warm enough for swimming from October to May, while it gets a little cool, but remains all in all acceptable, in July and August, when it drops to 22 °C (72 °F).
Pointe Noire - Sea temperature
Temp (°C)272829282624222224262727
Temp (°F)818284827975727275798181

When to go

The best time to visit the Republic of Congo runs from June to August, in fact it is the coolest and the driest, except in the north where it rains even during this period. However, even though it's not too hot, moisture is high and the sky is cloudy even in the centre and south, where it's the dry season. Remember that nights can be cool on the plateau, and even on the coast the weather can get a little cool, at least for swimming, also considering the lack of sunshine.
In August, at the end of the dry season, the animals of the savanna gather in the few remaining waterholes or along rivers, therefore they are easier to spot.

What to pack

All year round, light clothes, of natural fibres, a light sweatshirt for the evening, an umbrella or a light raincoat for showers during the rainy season. From June to September, you can add a sweatshirt or sweater and a light jacket, especially in the south and along the coast.