This graph displays return periods, either the annual exceedence inverse probability or as the inverse probability per wind speed bin, according to the parameter histf as set in the params.m file. The synthetic tracks are compared to historical tracks. The velocity used depends on the value of htype in the params file and the type of event set. The default value of 2 gives the maximum winds of each event within the specified distance of the point of interest, for a circular filter, or at the point that events cross over line segments for poly filters. (The "maximum winds" in this case are the maximum winds anywhere in the storm at the point it crosses one of the line segments in poly.) The value 1 gives the lifetime maximum wind for all events in the set, and the value of 3 gives the maximum wind at the point of interest when a circular filter is used. (For poly filters, choice 3 is the same as choice 2). Under the entry Histograms and return period plots in the params file, other aspects of the graph and data can be set including the range of best-track years to use, the range of wind speeds to consider, and the width of the wind speed bins.

If the parameter ebar is set to 'y' in the params file, this plot will also display, in shading, an estimate of the best-track sampling error. This estimate has been created by, for each wind speed bin, estimating the expected number of best-track events in that bin by multiplying the synthetic track frequency by the number of years in the best track data. Once this central estimate is obtained, the integer value of the 5th and 95th percentiles are obtained from a Poisson distribution with that central frequency estimate. The shading is between these bounds. In principle, 90% of the best track frequencies should lie within the shading if they represent the same distribution as the synthetic tracks.