Not only has tropical activity in the Atlantic Basin been slow this year, but also in all tropical areas around the globe. Although the number of named storms usually gets the most attention, it is only one factor in the determination of tropical activity. The National Oceanic and Atmospheric Administration (NOAA) also uses the strength and duration of each tropical storm to calculate what they call the Accumulated Cyclone Energy (ACE) index.
The combining of the number, strength and duration of tropical systems into a set mathematical equation can give a much better insight into the differences between tropical seasons rather than just counting the number of storms alone. Since good satellite records started in 1979, the year 2009 has the distinction of the having the lowest ACE index measured. In fact, there has been a noticeable decrease in tropical energy worldwide in the past few years.