Willoughby et al. (2006), Equation 1(a)
will1a(vmax_gl, r, Rmax, n)
Numeric vector of the tangential wind component of the maximum gradient wind speed, in meters per second
Numeric vector of radius from the storm center to the point you are measuring, in kilometers
Numeric vector of the radius at which the maximum wind occurs, in kilometers
A numeric vector of one of the parameters of the Willoughby model.