We are witnessing tonight the rapid intensification of a compact sub-synoptic low level vortex. Pretty impressive. Keep in mind the vorticity equation / basic dynamics of rotation ... convergence shrinking the area of rotation, conserving angular momentum, increasing angular velocity. Notice the sharp angle at which the wind is crossing the isobars, and how that angle increases toward the center of circulation. Consider a Rankine vortex, the critical radius of the edge of the inner solid body