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FIG. 28. Accumulated Cyclone Energy (ACE) Index indicating overall Atlantic basin tropical storm and hurricane activity for each June–November season between 1950 and 1999. The ACE index is calculated by summing the squares of the 6-hourly maximum sustained wind speed (Vmax2) for all named storms during their existence as a tropical storm or hurricane. Seasonal index values have been divided by 100,000 for display purposes only.