We investigate the hydrodynamic behavior of zeroes of trigonometric polynomials under repeated differentiation. We show that if the zeroes of a real-rooted, degree d trigonometric polynomial are distributed according to some probability measure ν in the large d limit, then the zeroes of its [2td]-th derivative, where t > 0 is fixed, are distributed according to the free multiplicative convolution of ν and the free unitary Poisson distribution with parameter t. In the simplest special case, our result states that the zeroes of the [2td]-th derivative of the trigonometric polynomial (sin θ2 ) 2d (which can be thought of as the trigonometric analogue of the Laguerre polynomials) are distributed according to the free unitary Poisson distribution with parameter t, in the large d limit. The latter distribution is defined in terms of the function ζ = ζt(θ) which solves the implicit equation ζ − t tan ζ = θ and satisfies ζt(θ) = θ + t tan(θ + t tan(θ + t tan(θ + . . .))), Im θ > 0, t > 0.