Weekly sonde observations in Suriname, supported by ECMWF analyses and a linear stability analysis, are used to analyze the recurrence of inertial instability as the ITCZ migrates over land during the South American Monsoon. A layer of cool moist air from the Atlantic Ocean is then advected southward over Suriname in the shape of a cold front, displacing the warmer air over the continent. The return flow northward, by the upper branch of the Hadley cell, is a region where inertial instability pervades due to cross-equatorial advection of anticyclonic vorticity and the proximity of the subtropical jet as it migrates closer to the Equator. This unstable region evidently leads to the episodical formation of a meridional sub-cell below the tropopause, where the damping is calculated to be strong enough to stabilize flow at smaller vertical scales, and yet weak enough to allow the observed cell recurrence - at approximately the inertial frequency of the underlying latitudes. This instability should also contribute to the Hadley cell formation through northward acceleration in the upper branch. The moist saturated conditions in the lower troposphere do allow inertial instability here, but the high damping values within the boundary layer suggests that the observed southward acceleration in the lower branch of the Hadley cell has a cause other than inertial instability.