Postscript to “Exact and general FT1 penultimate distributions of extreme wind speeds drawn from tail-equivalent Weibull parents”

We present a further contribution to the current debate on methodologies for assessing extreme wind speeds, adding further insights to a recent paper which derived exact and penultimate models for the FT1 distribution that account for asymptotic convergence and avoid the associated errors. This contribution addresses the issues of the upper tail shape of the parent distribution which controls the rate of convergence of the extreme to the asymptote and controls the power index of the variate of the penultimate model. We clear up two outstanding issues in the example data of the previous paper that resulted from contributions from more than one mechanism. We show that the Jenkinson-Lamb index may be used to separate the UK wind record into Cyclonic and Anti-cyclonic contributions, each of which is an excellent fit to one of a pair of Weibull distributions having similar shape parameters but differing scale parameters, that together form a disjoint parent distribution. It is the dominant Cyclonic component that controls the parameters of the penultimate distribution of extreme wind speeds in the UK, irrespective of direction.