This subject came up in the in-person class that I attended back in December, so I hope I can help clear this up for you.
First of all, it's not a type of burndown chart as such, but a means of visually representing estimates and their variance.
The Agile Practice Guide mentions "hurricane-style charts" in the side bar on p. 61, but, unhelpfully, there is no further explanation. What they are referring to are the kind of charts you might see on a TV weather forecast, where the predicted displacement and intensity of a hurricane are charted, overlayed over geographical maps. The resulting visual outcome is generally a cone, with predicted events in the near future having less variance (i.e. narrower section), and events further into the future are represented with a wider range of possibilities, giving a wider section. In project management, this is often called the "Cone of Uncertainty". If you search that term, you should find more useful information.