Map from Google - Togo

In Togo the climate is tropical, with a winter dry season, and a rainy season, due to the African monsoon, which runs from April to October in the centre and from May to October in the north, while along the coast there is a marked decrease in rainfall from July to September.
Rainfall ranges from 900 millimetres per year on the coast, to 1,000 mm in the far north, to 1,300/1,400 mm in the central and northern inland areas, up to about 2,000 mm in the western part of the Plateaux Region.

In the centre and north, winter is hot and dry, with maximum temperatures above 30 °C. The prevailing wind, the Harmattan blows from the desert, bringing sand and dust. Sometimes the temperature can rise close to 40 °C, on the other hand it can get cool at night, so that the minimum can touch 10 °C or even a little below.
Here are the average temperatures of Sokodé, located in the north-central, at 340 metres above sea level.
Average temperatures - Sokodé
SokodéJanFebMarAprMayJunJulAugSepOctNovDec
SokodéJFMAMJJASOND
Min (°C)182022222120202020201917
Max (°C)343535343230272829293233

Starting from February, the temperature increases, reaching easily 35/36 °C; in March and April early showers begin to break out, coming from the south, and prevent the temperature from rising further, however sometimes it exceeds 40 °C, especially in the north where the rains arrive later. Rainfall exceeds 100 mm per month starting from April in the centre and from May in the north. The rains continue to increase in intensity and frequency, peaking between July and September, when they typically exceed 200 mm per month.
Here is the average precipitation in Sokodé.
Average precipitation - Sokodé
SokodéJanFebMarAprMayJunJulAugSepOctNovDecYear
SokodéJFMAMJJASONDY
Prec. (mm)15154510515519022024526012530151420
Days1146912131516103292

Consequently, the amount of sunshine touches its minimum from July to September, and while the humidity is increased, the temperature is decreased, so that the maximum drops below 30 °C in July and August. Therefore, summer is the least hot season (in Togo and in French-speaking African countries, the rainy season is called "hivernage", which means "wintering"), even though it's the wettest, therefore a little muggy, especially in the north-central, i.e. far from the coast, while on the coast the heat is tempered by sea breezes.
The rains withdraw during the month of October, starting from the north. The humid wind from the south is replaced by the drier, but hotter Harmattan, which blows from the north-east.

Along the coast the climate is slightly different. The temperature is more stable, so that in the capital Lomé, the highs in winter are around 32 °C; the warming spring is less intense than in the north, then the temperatures drop to 28/29 °C from June to September. Winter is moist because the breeze, but sometimes the Harmattan can arrive here as well.
Average temperatures - Lomé
LoméJanFebMarAprMayJunJulAugSepOctNovDec
LoméJFMAMJJASOND
Min (°C)232425242423232223232323
Max (°C)323233323130282829303232

The rains from March to June increase rapidly, so that June is the rainiest month with about 200 mm. But then the rain decline, reaching a minimum in August, and rising again from mid-September to late October, when in any case it does not exceed 100/120 mm per month. However, the sky remains often cloudy and the humidity high even in August. In Lomé, 900 mm of rain fall in a year, so the amount of rain that falls on the coast is the lowest of all Togo, because of the summer break. In the eastern part of the coast the rains are a bit more abundant: in Grand Popo the rainfall amounts to 1,150 mm per year. Here is the average precipitation in Lomé.
Average precipitation - Lomé
LoméJanFebMarAprMayJunJulAugSepOctNovDecYear
LoméJFMAMJJASONDY
Prec. (mm)153580105155200551550155205895
Days125681053693159

Togo

For swimming, the sea in Togo is warm all year round. Near shoals, currents can be dangerous.
Sea temperature - Lomé
LoméJanFebMarAprMayJunJulAugSepOctNovDec
LoméJFMAMJJASOND
Sea (°C)282829292928262526272928

When to go

The best time to visit Togo is from November to February, because it is the driest and sunniest. During the day it can get very hot, especially in February, and the annoying Harmattan can blow, bringing dust from the desert, while at night it can get cool.
The worst period, being the rainiest, is May to June on the coast, and July to September in the interior.

What to pack

In winter: in Lomé and the coast, light clothes for the day, a light sweatshirt for the evening, light scarf for the wind full of dust. In the north, light clothing, a sweatshirt and a light jacket for the evening, light scarf or turban for the desert wind.

In summer: light clothing made of natural fibres, a light sweatshirt and a light raincoat for the rain showers; for women it's better to avoid shorts and miniskirts.