A widely used tool for analyzing the strength of a hurricane season is the Accumulated Cyclone Energy or ACE index. The ACE index combines the number, strength and duration of tropical systems into a set mathematical equation. This can give a much better insight into the differences between tropical seasons rather than just counting the number of storms alone.
For instance, although the North Atlantic Hurricane season has now recorded 11 named systems, the accumulated ACE score for the year is running at less than 30% of average. The average is based on the years 1981 through 2010. The North Atlantic basin is not the only region recording well below normal ACE scores this year. In fact, globally, all tropical regions are running below normal for ACE scores. Taken as a whole, global ACE numbers this year are running at only 54% of average.
The past several years have also recorded a below average ACE, likely attributed to a recent switch to cooler Pacific Ocean temperatures.