Hasetiho: Tobi Island's wake current system

What happens when an island sits in the middle of a current?
Tobi Currents
Tobian currents
drawing by Peter Black

Tobian currents described by Patricio Mohortihotimoh

Tobi Island's wake current system described by R.E. Johannes in Words of the Lagoon: Fishing and Marine Lore in the Palau District of Micronesia (Berkeley: University of California Press, 1981)

On the upstream end of an island the current divides and is directed past the island on either side.  Shoreward of the point where the current divides is an area of still, calm water with almost no current which Tobians call the suriyout.  Two narrow streams of turbulent water called arm extend downstream from the sides of the island, paralleling the prevailing current.  Five to forty meters wide, each arm is sufficiently rough so that crossing it in a canoe can be hazardous....These twin currents usually increase in width and decrease in turbulence with distance from the island.  They extend downstream for a variable distance, sometimes to a point from which the island can no longer be seen, gradually curving toward each other.  Ultimately they converge, creating an area of exceptionally rough water, called hapitsetse....Tobians said their hapitsetse disappears when the currents are weak....Leading back from the hapitsetse toward the island is a kind of backwash, or reverse current, running between the two arm....[p. 103]

Words of the Lagoon: Chapter 8 has a more detailed description of Tobi Island’s currents and their impact on fish behavior and fishing activity.

More on the Tobi wake—
Flow Past a Circular Cylinder on a β -Plane by D.L. Boyer and P.A. Davies
Effects of Island Mass
by W.M.Hamner and I.R. Hauri