Kumasi sits in Ghana's forest belt, so it is consistently humid and warm — daytime temperatures cluster between 25 and 32°C all year. The two rainy seasons run roughly from April to July (the heavier one) and September to November. Rains are usually brief, dramatic afternoon downpours rather than all-day grey.
The best stretch for travel is November to February, when the harmattan brings cooler nights, less rain, and clearer skies — though the harmattan haze can mute photographs. If you can time a visit to coincide with an Akwasidae festival at the Manhyia Palace, do so: the schedule of these forty-two-day cycles is published well in advance.