From AMS Glossary
(Also known as the East African Coastal Current.) A western boundary current in the Indian Ocean that flows permanently northward from 10°S along the east African coast.
During the northeast monsoon the Zanzibar Current flows against the wind, meeting the southward flowing Somali Current at 1°N in December, 4°S in February (when the Zanzibar Current is weakest), and at the equator in April. Throughout this period it continues across the equator as an undercurrent that feeds into the Equatorial Countercurrent. During the southwest monsoon season the current strengthens considerably, attaining speeds of 2 m s-1 and a transport of 15 Sv (15 × 106 m3 s-1) and feeding into the Somali Current, which flows northward during that season.