Accumulated cyclone energy


Accumulated cyclone energy is a measure used by various agencies including the National Oceanic and Atmospheric Administration and the India Meteorological Department to express the activity of individual tropical cyclones and entire tropical cyclone seasons. It uses an approximation of the wind energy used by a tropical system over its lifetime and is calculated every six hours. The ACE of a season is the sum of the ACEs for each storm and takes into account the number, strength, and duration of all the tropical storms in the season. The highest ACE calculated for a single storm is 82, for Hurricane/Typhoon Ioke in 2006.

Calculation

The ACE of a season is calculated by summing the squares of the estimated maximum sustained velocity of every active tropical storm, at six-hour intervals. Since the calculation is sensitive to the starting point of the six-hour intervals, the convention is to use 00:00, 06:00, 12:00, and 18:00 UTC. If any storms of a season happen to cross years, the storm's ACE counts for the previous year. The numbers are usually divided by 10,000 to make them more manageable. One unit of ACE equals and for use as an index the unit is assumed. Thus:
where vmax is estimated sustained wind speed in knots.
Kinetic energy is proportional to the square of velocity, and by adding together the energy per some interval of time, the accumulated energy is found. As the duration of a storm increases, more values are summed and the ACE also increases such that longer-duration storms may accumulate a larger ACE than more-powerful storms of lesser duration. Although ACE is a value proportional to the energy of the system, it is not a direct calculation of energy.
A related quantity is hurricane destruction potential, which is ACE but only calculated for the time where the system is a hurricane.

Atlantic basin ACE


Categories

A season's ACE is used by NOAA and others to categorize the hurricane season into 4 groups by its activity. Measured over the period 1951-2000 for the Atlantic basin, the median annual index was 87.5 and the mean annual index was 93.2. The NOAA categorization system divides seasons into:
According to the NOAA categorization system for the Atlantic, the most recent above-normal season is the 2019 season, the most recent near-normal season is the 2014 season, and the most recent below normal season is the 2015 season.

Hyperactivity

The term hyperactive is used by Goldenberg et al. based on a different weighting algorithm, which places more weight on major hurricanes, but typically equating to an ACE of about 153 or more.

Individual storms in the Atlantic

The highest ever ACE estimated for a single storm in the Atlantic is 73.6, for the San Ciriaco hurricane in 1899. This single storm had an ACE higher than many whole Atlantic storm seasons. Other Atlantic storms with high ACEs include Hurricane Ivan in 2004, with an ACE of 70.4, Hurricane Irma in 2017, with an ACE of 64.9, the Great Charleston Hurricane in 1893, with an ACE of 63.5, Hurricane Isabel in 2003, with an ACE of 63.3, and the 1932 Cuba hurricane, with an ACE of 59.8.
Since 1950, the highest ACE of a tropical storm was Tropical Storm Laura in 1971, which attained an ACE of 8.6. The highest ACE of a Category 1 hurricane was Hurricane Nadine in 2012, which attained an ACE of 26.3. The lowest ACE of a tropical storm were tropical storms Chris and Philippe, both of which were tropical storms for only six hours and had an ACE of just 0.1. The lowest ACE of any hurricane was 2005's Hurricane Cindy, which was only a hurricane for six hours, and 2007's Hurricane Lorenzo, which was a hurricane for twelve hours; both of which had an ACE of just 1.5. The lowest ACE of a major hurricane, was Hurricane Gerda in 1969, with an ACE of 5.3. The only years since 1950 to feature two storms with an ACE index of over 40 points have been 1966, 2003, and 2004, and the only year to feature three storms is 2017.
The following table shows those storms in the Atlantic basin from 1950–2019 that have attained over 50 points of ACE.
StormYearPeak classificationACEDuration
Hurricane Ivan2004
Category 5 hurricane
70.423 days
Hurricane Irma2017
Category 5 hurricane
64.913 days
Hurricane Isabel2003
Category 5 hurricane
63.314 days
Hurricane Donna1960
Category 4 hurricane
57.616 days
Hurricane Carrie1957
Category 4 hurricane
55.821 days
Hurricane Inez1966
Category 4 hurricane
54.621 days
Hurricane Luis1995
Category 4 hurricane
53.516 days
Hurricane Allen1980
Category 5 hurricane
52.312 days
Hurricane Esther1961
Category 5 hurricane
52.218 days
Hurricane Matthew2016
Category 5 hurricane
50.912 days

Atlantic hurricane seasons, 1851–2020

Due to the scarcity and imprecision of early offshore measurements, ACE data for the Atlantic hurricane season is less reliable prior to the modern satellite era, but NOAA has analyzed the best available information dating back to 1851. The 1933 Atlantic hurricane season is considered the highest ACE on record with a total of 259. For the current season or the season that just ended, the ACE is preliminary based on National Hurricane Center bulletins, which may later be revised.
SeasonACETSHUMHClassification
185136.24631Below normal
185273.28551Near normal
185376.49842Near normal
185431.00531Below normal
185518.12541Below normal
185648.94642Below normal
185746.84430Below normal
185844.79660Below normal
185955.73871Below normal
186062.06761Below normal
186149.71860Below normal
186246.03630Below normal
186350.35950Below normal
186426.55530Below normal
186549.13730Below normal
186683.65761Near normal
186759.97971Below normal
186834.65430Below normal
186951.021071Below normal
187087.811102Near normal
187188.39862Near normal
187265.38540Below normal
187369.47532Near normal
187447.05740Below normal
187572.48651Near normal
187656.05542Below normal
187773.36831Below normal
1878180.8512102Hyperactive
187963.63862Below normal
1880131.081192Near normal
188159.25740Below normal
188259.4675642Below normal
188366.7432Near normal
188472.06441Below normal
188558.3860Below normal
1886166.16512104Hyperactive
1887181.2619112Hyperactive
188884.945962Near normal
1889104.0425960Near normal
189033.345421Below normal
1891116.1051071Near normal
1892115.8375950Near normal
1893231.147512105Hyperactive
1894135.42754Near normal
189568.765620Below normal
1896136.0825762Near normal
189754.54630Below normal
1898113.23751151Near normal
1899151.0251052Near normal
190083.345732Near normal
190198.9751360Near normal
190232.65530Below normal
1903102.071071Near normal
190430.345640Below normal
190528.3775511Below normal
1906162.881163Near normal
190713.06500Below normal
190895.111061Near normal
190993.341264Near normal
191063.9531Below normal
191134.2875630Below normal
191257.2625741Below normal
191335.595640Below normal
19142.53100Below normal
1915130.095653Near normal
1916144.012515105Above normal
191760.6675422Below normal
191839.8725641Below normal
191955.04521Below normal
192029.81540Below normal
192186.53752Near normal
192254.515531Below normal
192349.31941Below normal
1924100.18751152Near normal
19257.2525410Below normal
1926229.55751186Hyperactive
192756.4775841Below normal
192883.475641Below normal
192948.0675531Below normal
193049.7725322Below normal
193147.8351331Below normal
1932169.66251564Hyperactive
1933258.5720116Hyperactive
193479.06751371Near normal
1935106.2125853Near normal
193699.7751771Near normal
193765.851141Near normal
193877.575942Near normal
193943.6825631Below normal
194067.79960Near normal
194151.765643Below normal
194262.4851141Below normal
194394.011052Near normal
1944104.45251483Near normal
194563.4151152Below normal
194619.6125730Below normal
194788.491052Near normal
194894.97751064Near normal
194996.44751672Near normal
1950211.282516116Hyperactive
1951126.3251283Above normal
195269.081152Near normal
195398.50751473Near normal
1954110.881673Near normal
1955158.171394Hyperactive
195656.67251241Below normal
195778.6625832Near normal
1958109.69251273Near normal
195977.10751472Near normal
196072.9842Near normal
1961205.3951285Hyperactive
196235.5675740Below normal
1963117.93251073Near normal
1964169.76751375Hyperactive
196584.331041Below normal
1966145.21751173Above normal
1967121.705861Near normal
196845.0725850Below normal
1969165.737518125Hyperactive
197040.181052Below normal
197196.52751361Near normal
197235.605730Below normal
197347.85841Below normal
197468.1251142Below normal
197576.0625963Near normal
197684.17251062Near normal
197725.3175651Below normal
197863.21751252Below normal
197992.9175962Near normal
1980148.93751192Near normal
1981100.32751273Near normal
198231.5025621Below normal
198317.4025431Below normal
198484.2951351Near normal
198587.98251173Near normal
198635.7925640Below normal
198734.36731Below normal
1988102.99251253Near normal
1989135.1251172Near normal
199096.80251481Near normal
199135.5375842Below normal
199276.2225741Below normal
199338.665841Below normal
199432.02730Below normal
1995227.102519115Hyperactive
1996166.18251396Hyperactive
199740.9275831Below normal
1998181.767514103Hyperactive
1999176.52751285Hyperactive
2000119.14251583Above normal
2001110.321594Near normal
200267.99251242Near normal
2003176.841673Hyperactive
2004226.881596Hyperactive
2005250.127528157Hyperactive
200678.5351052Near normal
200773.8851562Near normal
2008145.71751685Above normal
200952.58932Below normal
2010165.482519125Hyperactive
2011126.30251974Above normal
2012132.632519102Above normal
201336.121420Below normal
201466.725862Near normal
201562.6851142Below normal
2016141.25251574Above normal
2017224.877517106Hyperactive
2018132.58251582Above normal
2019132.20251863Above normal
202016.9200920Current season

Eastern Pacific ACE

Categories



The categorization of seasons for this table is based mutatis mutandis on that used in the Atlantic basin:
The highest ever ACE estimated for a single storm in the Eastern or Central Pacific, while located east of the International Date Line is 62.8, for Hurricane Fico of 1978. Other Eastern Pacific storms with high ACEs include Hurricane John in 1994, with an ACE of 54.0, Hurricane Kevin in 1991, with an ACE of 52.1, and Hurricane Hector of 2018, with an ACE of 50.5.
The following table shows those storms in the Eastern and Central Pacific basins from 1971–2018 that have attained over 40 points of ACE.
StormYearPeak classificationACEDuration
Hurricane Fico1978
Category 4 hurricane
62.820 days
Hurricane John 1994
Category 5 hurricane
54.019 days
Hurricane Kevin1991
Category 4 hurricane
52.117 days
Hurricane Hector 2018
Category 4 hurricane
50.513 days
Hurricane Tina1992
Category 4 hurricane
47.722 days
Hurricane Trudy1990
Category 4 hurricane
45.816 days
Hurricane Lane2018
Category 5 hurricane
44.213 days
Hurricane Dora 1999
Category 4 hurricane
41.413 days
Hurricane Jimena2015
Category 4 hurricane
40.015 days
Hurricane Guillermo1997
Category 5 hurricane
40.016 days

- Indicates that the storm formed in the Eastern/Central Pacific, but crossed 180°W at least once, therefore only the ACE and number of days spent in the EPAC/CPAC are included.

Eastern Pacific hurricane seasons, 1971–2020

Accumulated Cyclone Energy is also used in the eastern and central Pacific Ocean. Data on ACE is considered reliable starting with the 1971 season. The season with the highest ACE since 1971 is the 2018 season. The 1977 season has the lowest ACE. The most recent above-normal season is the 2018 season, the most recent near-normal season is the 2019 season, and the most recent below normal season is the 2013 season. The 35 year median 1971-2005 is 115 x 104 kn2 ; the mean is 130.
SeasonACETSHUMHClassification
197113918126Above normal
19721361484Above normal
19731141273Near normal
19749018113Near normal
19751121794Near normal
19761211595Near normal
197722840Below normal
197820719147Hyperactive
1979571064Below normal
1980771473Below normal
1981721581Below normal
198216123125Above normal
198320621128Hyperactive
198419321137Above normal
198519224138Above normal
19861071793Near normal
198713220104Near normal
19881271573Near normal
19891101794Near normal
199024521166Hyperactive
199117814105Above normal
1992295271610Hyperactive
199320115119Hyperactive
199418520105Above normal
19951001073Near normal
199653952Below normal
19971671997Above normal
19981341396Near normal
199990962Near normal
2000951962Near normal
2001901582Near normal
20021241586Near normal
2003561670Below normal
2004711263Below normal
2005961572Near normal
200615519116Above normal
2007521141Below normal
2008831772Below normal
20091272085Near normal
201052832Below normal
201112111106Near normal
20129817105Near normal
2013762091Below normal
201419922169Hyperactive
2015287261611Hyperactive
201618322136Above normal
20171001894Near normal
2018318231310Hyperactive
2019971974Near normal
202027.85411Current season