The vorticity equation $$\frac{D\vec{\omega}}{Dt}=\vec{\omega}\cdot\nabla\vec{u}-\vec{\omega}(\nabla\cdot\vec{u})+\frac{1}{\rho^2}\nabla\rho\times\nabla P$$

describes that convergence (decreasing area, $\nabla\cdot\vec u<0$) leads to increasing vorticity. Does this mean that the strongest tornadoes don't have the greatest vorticity, or am I missing something?