OBJECTIVE CLASSIFICATION OF ATLANTIC HURRICANES

Previous groupings of Atlantic tropical cyclone activity into baroclin ically influenced and tropical-only hurricanes have required subjectiv e evaluations. In this paper, a set of statistically significant and v alid rules are introduced that objectify this previously subjective ev aluation. This is done with the aid of classification trees. The tree classifications are better than 90% accurate with respect to an earlie r subjective discrimination. Objective classification rules are the ba sis for a climatology of Atlantic hurricanes. The average latitude of origin for tropical-only hurricanes is 18.8 degrees N, compared to 29. 1 degrees N for baroclinically influenced storms. The baroclinically i nfluenced hurricane season extends from-mid May to December, while the tropical-only season is largely confined to the months of August thro ugh October. There is a fairly abrupt shift to fewer numbers of tropic al-only hurricanes around 1960.