Kayes has one of the highest average temperatures of any city on earth. The hot season runs from March to June and can be almost unsurvivable without air conditioning — midday temperatures of 45–50°C are recorded regularly, and the harmattan wind from the Sahara adds dust to the heat. The city effectively shuts down in the hottest hours.
November through February is the only comfortable window. Temperatures are in the 25–35°C range during the day, cooler at night, with dry air and generally clear skies. This is also when the Sahel is at its most visually appealing — the landscape has browned but the light is extraordinary.
July through October is the rainy season: temperatures drop somewhat (to 35–40°C), and the Félou Falls are at their most dramatic — the full flow is an impressive spectacle. But roads can flood, transport becomes unreliable, and the humidity makes the heat feel worse. The river itself is dangerous for swimming during high water.
Current security conditions in Mali should be checked carefully before any travel. Large parts of the country outside the capital have been affected by conflict; Kayes in the far west has generally been more stable, but the situation changes.