Fox News Weather Center

How is the intensity of hurricane season measured?


Accumulated cyclone energy, or ACE, measures the strength of hurricanes and tropical storms over their duration. It allows meteorologists to compare different storms and seasons.

"We can classify how active a basin is for a particular season by defining the total ACE for that season plus the number of storms and major hurricanes," said AccuWeather Hurricane Expert Dan Kottlowski.

Irma thumbnail

GOES-16 satellite image of Hurricane Irma churning near Puerto Rico on Sept. 6, 2017. (Image/NOAA)


"The higher the ACE value for each storm, the stronger and potentially higher impacts it creates," he said.

The ACE value for a season in a particular region is the sum of the ACE of every tropical storm and hurricane that year. The average ACE value in the Atlantic Basic is about 92 units. An above-average season is about 111; a below-average season is 66.

It's only in recent history this measurement could be used for all storms, not just those that impacted land. Prior to the satellite era (before 1966), there was no way to track tropical storms that remained at sea. Once geostationary satellites were launched into the Earth's orbit in 1975, scientists had a more complete picture of the oceans to measure storms.

ACE infographic


The highest ACE ever reported for a hurricane was the San Ciriaco hurricane in 1899; the lowest ever recorded was 1.2 in 1959.

Thus far in 2017, the Atlantic hurricane season has been rather active. So far, there have been three storms this year with high ACE values. Hurricanes Irma, Maria and Jose reached 66.6, 44.6 and 42.2 units, respectively.

According to Colorado State University, the 2017 season has an ACE value of 223.2. Kottlowski said if there are two more storms before the end of November, that value could reach over 230 units, making it one of the most active hurricane seasons on record. However, the final total all depends on the duration and strength of any additional storms.