Map from Google - Ghana

In Ghana the climate is tropical, with a dry season in winter, and a rainy season in summer, related to the African monsoon. The rainy season lasts from May to September in the north, from April to October in the centre, and from April to November in the south. On the contrary, along the east coast the rainy season is shorter and goes from April to June, with a break in July and August and a slight recovery in September and October.

Climates in Ghana

The rainiest area is the south, where precipitation is above 1,500 millimetres per year, and even more so the small portion of the west coast, where it reaches 2,000 mm per year. The driest areas are the north, where the rainfall amount is around 1,000 mm per year, and the eastern seaboard, including the capital Accra, where it drops below 800 mm. Anyway, as we have said, in the north there's only one rainy season, reaching its height in the summer months, while in the coast the rainy season is divided into two.

Northern Ghana

In the centre and north, winter is hot: daytime temperatures are usually about 35 °C in December and January, even though the air is dry and the nights are cool. Sometimes at night, however, the weather can get a little cold in the centre-north, with lows around 10 °C.
From the desert, a hot, dust laden wind blows, called Harmattan. From February to April, the temperature increases further, easily surpassing 40 °C.
Here are the average temperatures of Bolgatanga, in the far north.
Average temperatures - Bolgatanga
BolgatangaJanFebMarAprMayJunJulAugSepOctNovDec
BolgatangaJFMAMJJASOND
Min (°C)192225262523222222222019
Max (°C)353739383633313031343635

Then comes the monsoon. In March in the centre and in April in the north, early showers and thunderstorms may occur, usually in the afternoon or evening, which become more substantial, exceeding 100 mm per month in the following month (ie April in the centre and May in the north). Under the blows of thunderstorms and clouds brought by the ocean currents, the temperatures gradually decrease, and from July to September, during the period of the maximum rainfall, it drops to around 30/31 °C, but the humidity increases and the cloudiness is by now common.
The rains cease in October in the north, and in November the centre; the return of the dry winds from the north produces a new increase of temperature: so both the sun and the heat come back. At the end of the year, rainfall amounts to 1,000 mm in the north and 1,200/1,300 mm in the centre, where as we have seen the rainy season is longer.
Here is the average precipitation in Tamalé, in the north-central.
Average precipitation - Tamalé
TamaléJanFebMarAprMayJunJulAugSepOctNovDecYear
TamaléJFMAMJJASONDY
Prec. (mm)2950901201301301902151001351054
Days013681010121691177

In the south, the winter is a bit less hot, so that the daytime temperatures are about 31/32 °C in December and January, and arrive to 34 °C in February; here there is almost no warming in spring, because the rains begin as early as March.
Here are the average temperatures of Kumasi, located in the south.
Average temperatures - Kumasi
KumasiJanFebMarAprMayJunJulAugSepOctNovDec
KumasiJFMAMJJASOND
Min (°C)202222222222212121222221
Max (°C)323433323130282829303131

The rainiest month is June, with 225 mm of rain; from mid-July to mid-September the rains decrease a bit, and then they resume to fall from mid-September to early November. In the south, 1,400/1,500 mm of rain fall in a year, even though east of Lake Volta and south-west of Kumasi the rainfall amount is even higher.
Here is the average precipitation in Kumasi.
Average precipitation - Kumasi
KumasiJanFebMarAprMayJunJulAugSepOctNovDecYear
KumasiJFMAMJJASONDY
Prec. (mm)25651351401902251157517020095301465
Days251010121511101417113120

Lake Volta

Along the east coast, where the capital Accra is located, the climate is a bit different: winter is similar to that of the rest of the south, that is, less hot but more humid than the north, so that daytime temperatures are about 32 °C, and it remains around 23/24 °C at night. Sometimes, however, the dry Harmattan can arrive even here. Here are the average temperatures of Accra.
Average temperatures - Accra
AccraJanFebMarAprMayJunJulAugSepOctNovDec
AccraJFMAMJJASOND
Min (°C)232424242423232222242423
Max (°C)323333323129292829313232

In spring, rains arrive earlier, with early showers already in March, and a peak in June, when precipitation reaches 200 mm per month. But after the rains fall sharply, so much so that in August just 10 mm of rain fall, because the so-called "Intertropical Convergence Zone", moves to the north. Nevertheless, from June to September, the sky usually remains cloudy. Even in the coast, as in the rest of the country, the summer months are the least hot of the year, and even here the humidity is high, indeed it is even higher than in inland areas, due to the proximity of the sea, but on the other hand there is the beneficial blow of the breeze, which reduces the feeling of stuffiness. In September and October, the rains resume a bit, but they do not reach 100 mm per month. In Accra, just 790 mm of rain per year fall, and basically the only very rainy months are May and June, and sometimes the first half of July.
Here is the average precipitation in Accra.
Average precipitation - Accra
AccraJanFebMarAprMayJunJulAugSepOctNovDecYear
AccraJFMAMJJASONDY
Prec. (mm)15357580145195501540804020790
Days125591153573258

Along the west coast, the rains are much more plentiful, and from May to mid-July they become really heavy, reaching even 500 mm per month; the summer break is evident here as well, and runs from mid-July to mid-September, but then the rains return substantial, although they do not reach the peaks of the first part of the rainy season; the rains linger on until December, so that here the only relatively dry months are January and February, as well as August. In this area, the rainfall reaches 2,000 mm per year.
Here is the average precipitation in Axim.
Average precipitation - Axim
AximJanFebMarAprMayJunJulAugSepOctNovDecYear
AximJFMAMJJASONDY
Prec. (mm)356512516532548017580100165130651910
Days571113171915151918117157

The sea in Ghana is warm enough for swimming all year round, although it gets a bit cooler from July to September.
Sea temperature - Accra
AccraJanFebMarAprMayJunJulAugSepOctNovDec
AccraJFMAMJJASOND
Sea (°C)272828292927252425272828

When to go

Generally, the best time to visit Ghana is winter, from December to February, because it is the driest and sunniest: the weather is generally good, although it's hot during the day in the centre-north. In the north, the best time is from November to January, because February get even hotter. In November, in the south the last rains occur, and even in December on the west coast. So the best month to visit Ghana as a whole is January.

What to pack

In winter: in Accra and the coast, light clothes for the day, a light sweatshirt for the evening, scarf for the wind-borne sand and dust. In the north, light clothing, a sweatshirt and a light jacket for the evening, scarf for the desert wind.

In summer: tropics-friendly, light clothing of natural fibres, umbrella, a light sweatshirt and a light raincoat for the rain showers.