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The NOAA Seasonal Outlook for Atlantic basin hurricane activity does not predict numbers of tropical storms, hurricanes and major hurricanes directly. Rather, the scheme is set up to forecast a range of expected values for the ACE index (Accumulated Cyclone Energy), a measure of overall activity. The ranges predicted for numbers of systems are obtained by looking at the years in the historical record which had observed values for ACE in the predicted range for the current year. Note that although the range for ACE might verify correctly for a given year (as it has so far for every year since the forecast began in 1998 -- see below), it is rare that the ranges for all three numbers (tropical storms, hurricanes and major hurricanes) will be correct. However, if ACE is correct, then usually at least two of the predicted ranges for numbers are correct as well. (Click here to see a chart of the observed values for ACE since 1950.)