Thanks go to John Kaplan and Jason Dunion for comments on an earlier manuscript draft, and to Mike Jankulak for his expert editing. The routines used to perform the discriminant analysis are from Roguewave’s IMSL Libraries, and special thanks to their support staff, especially Trudi Schweizer, for help in getting the routines to work properly.
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Both extratropical systems and remnant lows are now operationally classified by NHC as “posttropical.”
Hart and Evans (2001) showed that ~47% of Atlantic TCs undergo extratropical transition. These statistics show that ~10% of individual cases undergo ET. The current sample includes cases in which the TC did not undergo ET within 120 h of the initial time but may have later. Thus, these two values are not contradictory.
Individual cases are serially correlated with those from the same storm and within about 24 h of each other (Aberson and DeMaria 1994). The analysis with only those cases separated by at least 24 h is not appreciably different from the one presented here.
This skill score only accounts for yes–no forecasts. No skill score that can evaluate multiple category forecasts has come to the attention of the author.