Predicting when a three-dimensional turbulent flow reaches its dissipation peak is essential for both theory and adaptive algorithms in simulations and experiments. Using direct numerical simulations (DNSs) of the Taylor-Green vortex (TGV) at resolutions of ${256}^3-{1024}^3$, we introduce and test a small-scale weighted diagnostic: the spectrum of ${|\nabla \times \mathit{\omega }|}^2$ (with $\mathit{\omega }=\nabla \times \mathbf{u}$), which, for incompressible flow, is equivalent to a $k^4$-weighted energy spectrum. We show that the peak wavenumber of this spectrum, $k_{\mathrm{peak}}{\left[\right|\nabla \times \mathit{\omega }|}^2]$, advances rapidly to intermediate-small scales and then levels off before the dissipation rate $\varepsilon \left(t\right)={\sum }_{k}2\nu k^{2}E\left(k\right)$ reaches its maximum. Across all resolutions, we observe robust temporal ordering $t_k<t_{\varepsilon }<t_{\mathrm{\Pi }}$, where $t_k$ marks the onset of the rapid rise of $k_{\mathrm{peak}}{\left[\right|\nabla \times \mathit{\omega }|}^2], t_{\varepsilon }$ is the time of the maximal $\varepsilon \left(t\right)$, and $t_{\mathrm{\Pi }}$ is when the cumulative flux $\left|\mathrm{\Pi }\right(K\left)\right|$ attains its largest peak scale. This early-warning signal correlates with the morphological transition to filament-dominated structures visible in $Q$-criterion isosurfaces and is consistent with integral-scale trends ($L_{\mathrm{int}},\lambda ,\eta$). The diagnostic is simple to compute from standard DNS data and highlights the incipient formation of high-curvature structures, where viscosity acts most strongly.

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• Energy cascade
• Three-dimensional turbulence
• Vortex dynamics