Why can the coast from Ghana’s Cape Three Points to Benin receive less rainfall than other equatorial areas?

The coast from Ghana’s Cape Three Points to Benin experiences lower rainfall than other equatorial regions due to the specific behavior of the West African monsoon and the influence of dry air masses.12

While this area is located in the tropics, it experiences a "short drought" during the high-sun months of July and August. During this period, the southwesterly monsoon winds—which typically bring moisture—are at their strongest, but the air arriving at the coast originates from anticyclones located in the Southern Hemisphere. This air is dry, despite its direction of flow, leading to a period of reduced precipitation.2

Additionally, the region's climate is governed by the interplay between the humid maritime tropical air mass and the hot, dry continental air mass (the harmattan). The convergence zone between these air masses oscillates seasonally; when the dry continental air dominates, drought conditions prevail. In specific areas like the Accra Plains, these factors contribute to anomalously low annual precipitation, creating conditions more similar to the northern savanna than the surrounding forest zones.1