Accumulated cyclone energy

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Accumulated cyclone energy (ACE) is a measure used by various agencies including the National Oceanic and Atmospheric Administration (NOAA) 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. [1]

Calculation

The ACE of a season is calculated by summing the squares of the estimated maximum sustained velocity of every active tropical storm (wind speed 35 knots [65 km/h, 40 mph] or higher), 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. [2] The numbers are usually divided by 10,000 to make them more manageable. One unit of ACE equals 104  kn 2, and for use as an index the unit is assumed. Thus:

${\displaystyle {\text{ACE}}=10^{-4}\sum v_{\max }^{2}}$

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 (the mass of the moved air and therefore the size of the storm would show up in a real energy calculation).

A related quantity is hurricane destruction potential (HDP), which is ACE but only calculated for the time where the system is a hurricane. [3]

Atlantic basin ACE

50
100
150
200
250
300
1950
1960
1970
1980
1990
2000
2010
2020

Categories

A season's ACE is used by NOAA and others to categorize the hurricane season into 4 groups by its activity. [5] Measured over the period 19512000 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:

• Above-normal season: An ACE value above 111 (120% of the 1981–2010 median), provided at least two of the following three parameters are met: number of tropical storms: 13, hurricanes: 7, and major hurricanes: 3.
• Near-normal season: neither above-normal nor below normal and the next number of tropical storms: 12, hurricanes: 6, and major hurricanes: 2.
• Below-normal season: An ACE value below 66 (71.4% of the 1981–2010 median), or none of the following three parameters are exceeded: number of tropical storms: 9, hurricanes: 4, and major hurricanes: 1.

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. (2001) [6] based on a different weighting algorithm [7] , which places more weight on major hurricanes, but typically equating to an ACE of about 153 (175% of the 1951–2000 median) 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. [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 (2000) and Philippe (2017), 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 (Category 3 or higher), was Hurricane Gerda in 1969, with an ACE of 5.3. [9] 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. [10]

The following table shows those storms in the Atlantic basin from 1950–2019 that have attained over 40 points of ACE. [9]

StormYear Peak classification ACEDuration
Hurricane Ivan 2004
Category 5 hurricane
70.423 days
Hurricane Irma 2017
Category 5 hurricane
64.913 days
Hurricane Isabel 2003
Category 5 hurricane
63.314 days
Hurricane Donna 1960
Category 4 hurricane
57.616 days
Hurricane Carrie 1957
Category 4 hurricane
55.821 days
Hurricane Inez 1966
Category 4 hurricane
54.621 days
Hurricane Luis 1995
Category 4 hurricane
53.516 days
Hurricane Allen 1980
Category 5 hurricane
52.312 days
Hurricane Esther 1961
Category 5 hurricane
52.218 days
Hurricane Matthew 2016
Category 5 hurricane
50.912 days
Hurricane Flora 1963
Category 4 hurricane
49.416 days
Hurricane Edouard 1996
Category 4 hurricane
49.314 days
Hurricane Dorian 2019
Category 5 hurricane
48.915 days
Hurricane Beulah 1967
Category 5 hurricane
47.917 days
Hurricane Dog 1950
Category 4 hurricane
47.513 days
Hurricane Betsy 1965
Category 4 hurricane
47.018 days
Hurricane Frances 2004
Category 4 hurricane
45.915 days
Hurricane Faith 1966
Category 3 hurricane
45.417 days
Hurricane Maria 2017
Category 5 hurricane
44.814 days
Hurricane Ginger 1971
Category 2 hurricane
44.228 days
Hurricane David 1979
Category 5 hurricane
44.012 days
Hurricane Jose 2017
Category 4 hurricane
43.317 days
Hurricane Fabian 2003
Category 4 hurricane
43.214 days
Hurricane Hugo 1989
Category 5 hurricane
42.712 days
Hurricane Gert 1999
Category 4 hurricane
42.312 days
Hurricane Igor 2010
Category 4 hurricane
41.914 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,[ citation needed ] 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. [11] 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.

Hyperactive
Above Normal
Near Normal
Below normal
Accumulated Cyclone Energy
SeasonACE TS HU MH Classification
1851 36.24631Below normal
1852 73.28551Near normal
1853 76.49842Near normal
1854 31.00531Below normal
1855 18.12541Below normal
1856 48.94642Below normal
1857 46.84430Below normal
1858 44.79660Below normal
1859 55.73871Below normal
1860 62.06761Below normal
1861 49.71860Below normal
1862 46.03630Below normal
1863 50.35950Below normal
1864 26.55530Below normal
1865 49.13730Below normal
1866 83.65761Near normal
1867 59.97971Below normal
1868 34.65430Below normal
1869 51.021071Below normal
1870 87.811102Near normal
1871 88.39862Near normal
1872 65.38540Below normal
1873 69.47532Near normal
1874 47.05740Below normal
1875 72.48651Near normal
1876 56.05542Below normal
1877 73.36831Below normal
1878 180.8512102Hyperactive
1879 63.63862Below normal
1880 131.081192Near normal
1881 59.25740Below normal
1882 59.4675642Below normal
1883 66.7432Near normal
1884 72.06441Below normal
1885 58.3860Below normal
1886 166.16512104Hyperactive
1887 181.2619112Hyperactive
1888 84.945962Near normal
1889 104.0425960Near normal
1890 33.345421Below normal
1891 116.1051071Near normal
1892 115.8375950Near normal
1893 231.147512105Hyperactive
1894 135.42754Near normal
1895 68.765620Below normal
1896 136.0825762Near normal
1897 54.54630Below normal
1898 113.23751151Near normal
1899 151.0251052Near normal
1900 83.345732Near normal
1901 98.9751360Near normal
1902 32.65530Below normal
1903 102.071071Near normal
1904 30.345640Below normal
1905 28.3775511Below normal
1906 162.881163Near normal
1907 13.06500Below normal
1908 95.111061Near normal
1909 93.341264Near normal
1910 63.9531Below normal
1911 34.2875630Below normal
1912 57.2625741Below normal
1913 35.595640Below normal
1914 2.53100Below normal
1915 130.095653Near normal
1916 144.012515105Above normal
1917 60.6675422Below normal
1918 39.8725641Below normal
1919 55.04521Below normal
1920 29.81540Below normal
1921 86.53752Near normal
1922 54.515531Below normal
1923 49.31941Below normal
1924 100.18751152Near normal
1925 7.2525410Below normal
1926 229.55751186Hyperactive
1927 56.4775841Below normal
1928 83.475641Below normal
1929 48.0675531Below normal
1930 49.7725322Below normal
1931 47.8351331Below normal
1932 169.66251564Hyperactive
1933 258.5720116Hyperactive
1934 79.06751371Near normal
1935 106.2125853Near normal
1936 99.7751771Near normal
1937 65.851141Near normal
1938 77.575942Near normal
1939 43.6825631Below normal
1940 67.79960Near normal
1941 51.765643Below normal
1942 62.4851141Below normal
1943 94.011052Near normal
1944 104.45251483Near normal
1945 63.4151152Below normal
1946 19.6125730Below normal
1947 88.491052Near normal
1948 94.97751064Near normal
1949 96.44751672Near normal
1950 211.282516116Hyperactive
1951 126.3251283Above normal
1952 69.081152Near normal
1953 98.50751473Near normal
1954 110.881673Near normal
1955 158.171394Hyperactive
1956 56.67251241Below normal
1957 78.6625832Near normal
1958 109.69251273Near normal
1959 77.10751472Near normal
1960 72.9842Near normal
1961 205.3951285Hyperactive
1962 35.5675740Below normal
1963 117.93251073Near normal
1964 169.76751375Near normal
1965 84.331041Below normal
1966 145.21751173Above normal
1967 121.705861Near normal
1968 45.0725850Below normal
1969 165.737518125Hyperactive
1970 40.181052Below normal
1971 96.52751361Near normal
1972 35.605730Below normal
1973 47.85841Below normal
1974 68.1251142Below normal
1975 76.0625963Near normal
1976 84.17251062Near normal
1977 25.3175651Below normal
1978 63.21751252Below normal
1979 92.9175962Near normal
1980 148.93751192Near normal
1981 100.32751273Near normal
1982 31.5025621Below normal
1983 17.4025431Below normal
1984 84.2951351Near normal
1985 87.98251173Near normal
1986 35.7925640Below normal
1987 34.36731Below normal
1988 102.99251253Near normal
1989 135.1251172Near normal
1990 96.80251481Near normal
1991 35.5375842Below normal
1992 76.2225741Below normal
1993 38.665841Below normal
1994 32.02730Below normal
1995 227.102519115Hyperactive
1996 166.18251396Hyperactive
1997 40.9275831Below normal
1998 181.767514103Hyperactive
1999 176.52751285Hyperactive
2000 119.14251583Above normal
2001 110.321594Near normal
2002 67.99251242Near normal
2003 176.841673Hyperactive
2004 226.881596Hyperactive
2005 250.127528157Hyperactive
2006 78.5351052Near normal
2007 73.8851562Near normal
2008 145.71751685Above normal
2009 52.58932Below normal
2010 165.482519125Hyperactive
2011 126.30251974Above normal
2012 132.632519102Above normal
2013 36.121420Below normal
2014 66.725862Near normal
2015 62.6851142Below normal
2016 141.25251574Above normal
2017 224.877517106Hyperactive
2018 132.58251582Above normal
2019 132.20251863Above normal
2020 1.79100Current season

Eastern Pacific ACE

Categories

100
200
300
400
1961
1970
1980
1990
2000
2010

The (unofficial) categorization of seasons for this table is based mutatis mutandis on that used in the Atlantic basin:

• Near-normal season: neither above-normal nor below normal
• Above-normal season: An ACE value above 135 (117% of the median), provided at least two of the following three parameters exceed the long-term average:
• number of tropical storms (16)
• hurricanes (9)
• major hurricanes (4)
• Hyperactive season: An ACE value above 194, provided that preceding criteria are met
• Below-normal season: An ACE value below 86 (75% of the median)
Observed monthly values for the PDO index, 1900–present.
Historical East Pacific Seasonal Activity, 1981–2015.

Individual storms in the Eastern Pacific (east of 180°W)

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. [12]

The following table shows those storms in the Eastern and Central Pacific basins from 1971–2018 that have attained over 30 points of ACE. [13]

StormYear Peak classification ACEDuration
Hurricane Fico 1978
Category 4 hurricane
62.820 days
Hurricane John 1994
Category 5 hurricane
54.019 days
Hurricane Kevin 1991
Category 4 hurricane
52.117 days
Hurricane Hector 2018
Category 4 hurricane
50.513 days
Hurricane Tina 1992
Category 4 hurricane
47.722 days
Hurricane Trudy 1990
Category 4 hurricane
45.816 days
Hurricane Lane 2018
Category 5 hurricane
44.213 days
Hurricane Dora 1999
Category 4 hurricane
41.413 days
Hurricane Jimena 2015
Category 4 hurricane
40.015 days
Hurricane Guillermo 1997
Category 5 hurricane
40.016 days
Hurricane Norbert 1984
Category 4 hurricane
39.612 days
Hurricane Norman 2018
Category 4 hurricane
36.612 days
Hurricane Celeste 1972
Category 4 hurricane
36.316 days
Hurricane Sergio 2018
Category 4 hurricane
35.513 days
Hurricane Lester 2016
Category 4 hurricane
35.414 days
Hurricane Olaf 2015
Category 4 hurricane
34.612 days
Hurricane Jimena 1991
Category 4 hurricane
34.512 days
Hurricane Doreen 1973
Category 4 hurricane
34.316 days
Hurricane Ioke 2006
Category 5 hurricane
34.27 days
Hurricane Marie 1990
Category 4 hurricane
33.114 days
Hurricane Orlene 1992
Category 4 hurricane
32.412 days
Hurricane Greg 1993
Category 4 hurricane
32.313 days
Hurricane Hilary 2011
Category 4 hurricane
31.29 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, 1971–2019

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. [14] The 35 year median 19712005 is 115 x 104 kn2 (100 in the EPAC zone east of 140°W, 13 in the CPAC zone); the mean is 130 (112 + 18).

Hyperactive
Above Normal
Near Normal
Below normal
Accumulated Cyclone Energy
SeasonACE TS HU MH Classification
1971 13918126Above normal
1972 1361484Above normal
1973 1141273Near normal
1974 9018113Near normal
1975 1121794Near normal
1976 1211595Near normal
1977 22840Below normal
1978 20719147Hyperactive
1979 571064Below normal
1980 771473Below normal
1981 721581Below normal
1982 16123125Above normal
1983 20621128Hyperactive
1984 19321137Above normal
1985 19224138Above normal
1986 1071793Near normal
1987 13220104Near normal
1988 1271573Near normal
1989 1101794Near normal
1990 24521166Hyperactive
1991 17814105Above normal
1992 295271610Hyperactive
1993 20115119Hyperactive
1994 18520105Above normal
1995 1001073Near normal
1996 53952Below normal
1997 1671997Above normal
1998 1341396Near normal
1999 90962Near normal
2000 951962Near normal
2001 901582Near normal
2002 1241586Near normal
2003 561670Below normal
2004 711263Below normal
2005 961572Near normal
2006 15519116Above normal
2007 521141Below normal
2008 831772Below normal
2009 1272085Near normal
2010 52832Below normal
2011 12111106Near normal
2012 9817105Near normal
2013 762091Below normal
2014 19922169Hyperactive
2015 287261611Hyperactive
2016 18322136Above normal
2017 1001894Near normal
2018 318231310Hyperactive
2019 971974Near normal

Related Research Articles

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The 1994 Pacific hurricane season was the final season of the eastern north Pacific's consecutive active hurricane seasons that unofficially started in 1982. The season officially started on May 15, 1994, in the eastern Pacific, and on June 1, 1994, in the central Pacific, and lasted until November 30, 1994. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. The first tropical cyclone formed on June 18, while the last system dissipated on October 26. This season, twenty-two tropical cyclones formed in the north Pacific Ocean east of the dateline, with all but two becoming tropical storms or hurricanes. A total of 10 hurricanes occurred, including five major hurricanes. The above average activity in 1994 was contributed to the ongoing 1990-95 El Niño at the time.

The 1990 Pacific hurricane season was a very active season which observed 21 named storms within the basin. The season also produced the fourth highest ACE index value on record. The season was officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. However, these bounds were slightly exceeded when Hurricane Alma formed on May 12.

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Tropical cyclones are ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basin(s) they are located in. Only a few scales of classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but some alternative scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, usually between the months of June and November. A hurricane differs from a cyclone or typhoon only on the basis of location. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean.

Tropical cyclone seasonal forecasting is the process of predicting the number of tropical cyclones in one of the world's seven tropical cyclone basins during a particular tropical cyclone season. In the north Atlantic Ocean, one of the most widely publicized annual predictions comes from the Tropical Meteorology Project at Colorado State University. These reports are written by Philip J. Klotzbach and William M. Gray.

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The 2014 Pacific hurricane season was the fifth-busiest season since reliable records began in 1949, alongside the 2016 season. The season officially started on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin.

The 2012 Atlantic hurricane season was the final year in a consecutive string of three very active seasons, although many of the storms were weak and short-lived. It is tied with 1887, 1995, 2010, and 2011 for having the third-most named storms on record. It was also the third-costliest season, behind 2005 and 2017. The season officially began on June 1 and ended on November 30, dates that conventionally delimit the period during each year in which most tropical cyclones form in the Atlantic Ocean. However, Alberto, the first system of the year, developed on May 19 – the earliest date of formation since Tropical Storm Ana in 2003. A second tropical cyclone, Beryl, developed later that month. This was the first occurrence of two pre-season named storms in the Atlantic basin since 1951. It moved ashore in North Florida on May 29 with winds of 65 mph (100 km/h), making it the strongest pre-season storm to make landfall in the Atlantic basin. This season marked the first time since 2009 where no tropical cyclones formed in July. Another record was set by Hurricane Nadine later in the season; the system became the fourth-longest-lived tropical cyclone ever recorded in the Atlantic, with a total duration of 22.25 days. The final storm to form, Tony, dissipated on October 25 – however, Hurricane Sandy, which formed before Tony, became extratropical on October 29.

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The 2014 Atlantic hurricane season was a well below average season in terms of named storms, and an average season in terms of both hurricanes and major hurricanes. It produced nine tropical cyclones, eight named storms, the fewest since the 1997 Atlantic hurricane season, six hurricanes and two major hurricanes. It officially began on June 1, 2014, and ended on November 30, 2014. These dates historically describe the period each year when most tropical cyclones form in the Atlantic basin. The first storm of the season, Arthur, developed on July 1, while the final storm, Hanna, dissipated on October 28, about a month prior to the end of the season.

The 2016 Atlantic hurricane season was the first above-average hurricane season since 2012, producing 15 named storms, 7 hurricanes and 4 major hurricanes. The season officially started on June 1 and ended on November 30, though the first storm, Hurricane Alex which formed in the Northeastern Atlantic, developed on January 12, being the first hurricane to develop in January since 1938. The final storm, Otto, crossed into the Eastern Pacific on November 25, a few days before the official end. Following Alex, Tropical Storm Bonnie brought flooding to South Carolina and portions of North Carolina. Tropical Storm Colin in early June brought minor flooding and wind damage to parts of the Southeastern United States, especially Florida. Hurricane Earl left 94 fatalities in the Dominican Republic and Mexico, 81 of which occurred in the latter. In early September, Hurricane Hermine, the first hurricane to make landfall in Florida since Hurricane Wilma in 2005, brought extensive coastal flooding damage especially to the Forgotten and Nature coasts of Florida. Hermine was responsible for five fatalities and about \$550 million (2016 USD) in damage.

The 2020 Atlantic hurricane season is an ongoing event in the annual cycle of tropical cyclone formation. The season officially starts on June 1 and ends on November 30, dates that conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. However, the formation of tropical cyclones is possible at any time, as shown by the formation of Tropical Storm Arthur on May 16, marking the sixth consecutive year with a pre-season system.

During 2004, tropical cyclones formed within seven different tropical cyclone basins, located within various parts of the Atlantic, Pacific and Indian Oceans. During the year, a total of 130 systems formed with 81 of these developing further and were named by the responsible warning centre. The strongest tropical cyclone of the year was Cyclone Gafilo, which was estimated to have a minimum barometric pressure of 895 hPa (26.43 inHg).

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