Map from Google - Congo

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.
Average temperatures - Ouesso
OuessoJanFebMarAprMayJunJulAugSepOctNovDec
OuessoJFMAMJJASOND
Min (°C)202021212121212121212120
Max (°C)313232323130292930303030
Min (°F)686870707070707070707068
Max (°F)889090908886848486868686

However, in the north there are two more rainy periods, due to the passages of the sun at its zenith, and two periods which are relatively dry, December to February and June to August; in addition, the more we go to the north, the more evident is the first (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 rainfall in the north is better distributed, so it is covered by the forest, while the central and southern areas are covered by savanna.
Here is the average precipitation in Ouesso.
Average precipitation - Ouesso
OuessoJanFebMarAprMayJunJulAugSepOctNovDecYear
OuessoJFMAMJJASONDY
Prec. (mm)558015013015011580155220220150851590
Prec.(in)2.23.15.95.15.94.53.16.18.78.75.93.362.6
Days45981196101314116106

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 rainfall amount 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). 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 is the average precipitation in Pointe Noire.
Average precipitation - Pointe Noire
Pointe NoireJanFebMarAprMayJunJulAugSepOctNovDecYear
Pointe NoireJFMAMJJASONDY
Prec. (mm)1502102251809010213701651451251
Prec.(in)5.98.38.97.13.5000.10.52.86.55.749.3
Days10101211500141012984

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), while at night they remain quite high, around 18/20 °C (64/68 °F), due to the mitigating effect of the sea, as we can see from the averages of Pointe Noire.
Average temperatures - Pointe Noire
Pointe NoireJanFebMarAprMayJunJulAugSepOctNovDec
Pointe NoireJFMAMJJASOND
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.
Average temperatures - Brazzaville
BrazzavilleJanFebMarAprMayJunJulAugSepOctNovDec
BrazzavilleJFMAMJJASOND
Min (°C)212122222118171820212121
Max (°C)303131323028272830303029
Min (°F)707072727064636468707070
Max (°F)868888908682818286868684

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.
Average precipitation - Brazzaville
BrazzavilleJanFebMarAprMayJunJulAugSepOctNovDecYear
BrazzavilleJFMAMJJASONDY
Prec. (mm)12012518521013521231402251951343
Prec.(in)4.74.97.38.35.30.100.10.15.58.97.752.9
Days981013800039131285

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.
The amount of sunshine is never excellent throughout Congo, and it does not get better in the dry 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

For swimming, the sea is warm from October to May, while it gets a little cool, but still acceptable, in July and August, when it drops to 22 °C (72 °F).
Sea temperature - Pointe Noire
Pointe NoireJanFebMarAprMayJunJulAugSepOctNovDec
Pointe NoireJFMAMJJASOND
Sea (°C)272829282624222224262727
Sea (°F)818284827975727275798181

When to go

The best time to visit the Republic of Congo runs from June to August, being 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 it 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, umbrella or 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.