Upwelling along the northern coast of the Gulf of Guinea occurs only between June and October even though the local winds are favorable for upwelling throughout the year and have no seasonal variability. Away from the coast, near the equator for example, the winds do vary seasonally and cause large scale oceanographic conditions in the Gulf of Guinea to change seasonally....
Philander, S. G.. 1979. "Upwelling in the Gulf of Guinea." Journal of Marine Research 37, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1457