Assessing the Great Whirl, despite all the pirates
Each year, the powerful southwest monsoon ramps up in midsummer, bringing life-giving rains to the Indian subcontinent. The monsoon winds also drive dramatic changes in the regional ocean currents, including a reversal in the circulation of the Arabian Sea, an energetic eddy field, and strong coastal upwelling. Off the east coast of Somalia, a large (300 to 550 kilometer wide, or 186 to 342 mile wide) anticyclone appears—known since 1876 as the Great Whirl—with surface currents as strong as 2.5 meters per second (8.2 feet per second). The Great Whirl, while associated with the seasonal arrival of the southwest monsoon, is not caused entirely by it; the circulation of the Great Whirl starts a month before, and persists for a month after, the monsoon.