Fujita cycloidal estimate
Cycloidal wind estimator
Enter the measured loop width, the radius from the tornado center to the suction-vortex path, and the parent tornado forward speed. The tool solves Fujita's cycloidal-mark equation for n, then estimates rotational and maximum ground-relative wind.
W / (2R) = [sqrt(n^2 - 1) - pi/2 + asin(1/n)] / n
Use the same distance unit for W and R. This is an experimental estimate from ground marks, not an official rating method.
Pixel measuring helper
Measure from a photo
W: -- px
R: -- px
W/(2R): --
Upload a screenshot, click two endpoints for the loop width W, then switch to R and click two endpoints for the radius. Pixel units are fine because the equation only needs W divided by 2R.
n ratio
--
vortex rotational speed / forward speed
Rotational
--
Vrot = nT
Max estimate
--
Vmax = T(1 + n)
Enter values and calculate to see the cycloidal estimate.
WWidth of the cycloidal loop or scallop mark.
RRadius from the main tornado center to the suction-vortex path.
TParent tornado forward speed.
nSpeed ratio solved from Fujita's cycloidal equation.