Meteorologist: 2nd year in a row with below-normal tropical activity in N. Hemisphere – No Hurricanes hit U.S. for first time in a decade

Accumulated Cyclone Energy (ACE)
The Accumulated Cyclone Energy or ACE metric was originally created by Dr. William Gray and associates at Colorado State University, and it was later tweaked by NOAA. This is perhaps the best metric to measure overall tropical activity (as opposed to, for example, the number of storms) – as it not only factors in the intensity of a tropical cyclone, but it considers its longevity.  A “major” (category 3 or higher) hurricane, for example, that lasts for a long time will have a much bigger impact on the Accumulated Cyclone Energy than a short-lived and weaker tropical system.
Pacific Ocean
The Pacific Ocean is so large it is generally split into two sectors by meteorologists in the tracking of tropical activity using the international date line as the divider. The western part of the Pacific Ocean is the most important when it comes to global tropical activity as suggested by the climatological ACE which outweighs all other sectors of the northern hemisphere. The ACE levels for 2025 were slightly below-normal east of the date line and well below-normal in the all-important western Pacific.  In fact, this crucial part of the Pacific Ocean has experienced below-normal activity during each of the past 7 years with seasonal ACE levels in each of those years below the average for the 1991-2020 baseline period. Interestingly, the number of storms in the western Pacific Ocean this season was above normal, suggesting the ACE level per storm was below the averages (i.e., more storms than normal, but they were weaker and of shorter duration compared to normal).

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