What Accumulated Cyclone Energy Says About 2025
The 2025 Atlantic hurricane season produced an ACE of 130.8, seven percent above the 1991–2020 normal, despite having fewer named storms and hurricanes than average.
Timeline
- June 1, 2025: The official Atlantic hurricane season began.
- August–October 2025: Major hurricanes Erin, Gabrielle, Humberto and Melissa generated most of the basin's ACE.
- November 30, 2025: The official season ended with total basin ACE later calculated at 130.8.
The National Hurricane Center's final table gives the 2025 North Atlantic season an Accumulated Cyclone Energy value of 130.8. That was about seven percent above the 1991–2020 normal. The season produced 13 named storms, five hurricanes and four major hurricanes, showing why storm counts and total storm energy can tell different stories. [1][2]
ACE is calculated by taking a storm's maximum sustained wind speed in knots every six hours while it is at least tropical-storm strength, squaring each value and summing the results. The published number is scaled for readability. Squaring the wind speed gives intense hurricanes much more weight than weak tropical storms, while repeated six-hour observations reward longevity. [1]
The measure is useful because it combines how strong storms became with how long they maintained that strength. A short-lived tropical storm adds little. A powerful hurricane that remains over open water for many days can add a great deal even if it never makes landfall. ACE therefore describes basin activity, not land damage or danger to one city. [1][2]
Three storms dominated the total. The final NHC table assigns ACE values of 31.8 to Erin, 26.5 to Humberto and 34.3 to Melissa. Together they contributed 92.6 units, about 71 percent of the basin total. Gabrielle added another 18.5, so a small group of major hurricanes outweighed the relatively low overall storm count. [1]
This produced the season's central contrast. Thirteen named storms were one below the climate normal and five hurricanes were two below it, yet four major hurricanes were one above normal and basin ACE was above normal. The NHC verification report also noted three Category 5 hurricanes, the second-highest seasonal total on record behind 2005. [1][2]
ACE has important limits. It does not include storm surge, rainfall, flooding, tornadoes, geographic exposure or the vulnerability of buildings and infrastructure. It also omits periods below tropical-storm strength. A lower-ACE storm can be catastrophic if it strikes a vulnerable coast, while a high-ACE hurricane can spend much of its life far from land. [1]
For 2025, ACE answers a specific question: how much sustained wind energy accumulated across named Atlantic storms under the standard index. The answer, 130.8, indicates modestly above-normal basin activity driven mainly by several major hurricanes. It should be used alongside track, rainfall, surge, fatalities and damage data when judging the season's human impact. [1][2]
Sources
- National Hurricane Center — 2025 Atlantic hurricane season summary
- National Hurricane Center — 2025 hurricane-season forecast verification report