The development and decay of the large eddy in the northern Somali Basin and its smaller associated eddies each southwest moonsoon in the northwestern Indian Ocean has been monitored for four consecutive years by a time series of temperature sections obtained along the tanker sea lane across the Somali Basin. The evidence suggests that the large eddy first forms between 4 ¿N to 12 ¿N during late May and tends to remain approximately in this location throughout the entire southwest monsoon.