  In this paper, we calculate the region of emergence of rogue waves in the
Sasa-Satsuma equation by performing Penrose stability analysis. We consider
Wigner-transformed Sasa-Satsuma equation and separate out unstable solutions,
namely Penrose instability modes. We superpose these modes in a small region.
With the help of marginal property of the Wigner transform we identify the
region in which rogue wave solution can emerge in the Sasa-Satsuma equation and
calculate the amount of spatial localization. We also formulate a condition for
the emergence of rogue wave solution in the Sasa-Satsuma equation.
