Turbulent convection from a localized circular top surface into a rotating, homogeneous layer has been investigated in a cylindrical laboratory tank. The initial conditions for the experiments were selected so that the aspect ratio R/H≫1 and a three-dimensional turbulent layer penetrated with speed u≈(0.6¿0.1)(B0h)1/3 and then spread radially in the form of a gravity front upon reaching the bottom of the tank (here B0 is the buoyancy flux, h is the local depth, H is the total depth, and R is the radius of the source). This front later underwent a baroclinic instability generating mesoscale vortices with maximum density g'≈(10¿1)(B0R)2/3/H. Measurements and theoretical arguments have enabled us to scale the number of vortices N≈(1.5¿0.3)(R0,R)-2/3(R/H)-3/5, their mean diameter D/R≈8((R0,R)2/3, swirl velocity &ngr;≈(B0R)1/3, and relative vorticity f'/f≈0.5 (here (R0,R)=(B0/f3R2)1/2 is a Rossby number based on R, and f is the Coriolis parameter). An application of the present study to deep convective events observed in the Golfe du Lions compares favorably with the field observations.¿ 1997 American Geophysical Union