# Accumulated cyclone energy

Accumulated cyclone energy (ACE) is a metric used by various agencies to express the energy used by a tropical cyclone during its lifetime. The calculation takes a tropical cyclone's maximum sustained winds every six hours and multiplies it by itself to generate the values. These values are then added together which become a total for a storm and can either be divided by 10,000 to make them more manageable or added to other totals in order to work out a total for a particular group of storms. The calculation was originally created by William Gray and his associates at Colorado State University as the Hurricane Destruction Potential index, which took each hurricane's maximum sustained winds above 65 kn (120 km/h; 75 mph) and multiplied it by itself every six hours. This index was subsequently tweaked by the United States National Oceanic and Atmospheric Administration in 2000 to include all tropical cyclones, with winds above 35 kn (65 km/h; 40 mph) and renamed accumulated cyclone energy. The index has since been used by various other agencies to calculate a storm's accumulated cyclone energy, including the Australian Bureau of Meteorology as well as the India Meteorological Department.

The highest ACE calculated for a single storm is 82, for Hurricane/Typhoon Ioke in 2006.[1]

## History

The accumulated cyclone energy index was originally created by William Gray and his associates at Colorado State University, as the Hurricane Destruction Potential index (HDP).[2] They argued that the destruction of a hurricanes wind and storm surge was better related, to the square of the storms maximum winds (Vmax2) than to the storms maximum winds.[3] The index was calculated by squaring the estimated maximum sustained wind speed by themselves, for all tropical cyclones with windspeeds of above 65 kn (120 km/h; 75 mph) every six hours over the entire season.[2][3] This scale was subsequently tweaked by the United States National Oceanic and Atmospheric Administration (NOAA) to include all tropical cyclones, with winds above 35 kn (65 km/h; 40 mph) who also renamed it the accumulated cyclone energy index.[2] Since the scale was tweaked by NOAA, the storm totals have been used in a number of different ways, by various agencies and researchers, including the Australian Bureau of Meteorology and the India Meteorological Department.[4][5] These purposes include to categorise how active a tropical cyclone season was as well as to identify possible long-term trends in a certain area such as the Lesser Antiles.[6]

## Calculation

The accumulated cyclone energy of a season is calculated by summing the squares of the estimated maximum sustained velocity of every tropical cyclone that has wind speeds of 35 kn (65 km/h; 40 mph) or higher, at six-hour intervals. The numbers are usually divided by 10,000 to make them more manageable. One unit of ACE equals 104 kn2, 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 roughly proportional to the definite integral over time of the kinetic 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).

## Atlantic basin

Accumulated cyclone energy of North Atlantic hurricanes.[7]

Within the Atlantic Ocean, the United States National Oceanic and Atmospheric Administration and others, use the ACE index of a season to classify the season into one of four categories.[6] These four categories are extremely active season, above-, near- and below-normal average, and are worked out using an approximate tercile partitioning of seasons based on the ACE index, number of tropical storms, hurricanes and major hurricanes over the 30 years between 1981 and 2010.[6] The mean value of the ACE Index from 1991 to 2020 is 122.1 x 104 kt2, while the median value is 129.5 x 104 kt2.[6]

For a season to be defined as above normal, the ACE index criterion and two or more of the other criteria given in the table below must be satisfied. For a season to be defined as below normal, either the ACE index criterion must be satisfied, or all three of the other criteria must be satisfied.[6]

An extremely active season is simply defined as one with an ACE index above 159.6 x 104 kt2.[6] Confusingly, this means that a season could simultaneously be extremely active and near-normal (or even below normal). This is currently the case only for the 1906 season.

Classification criteria
Category ACE Index % of 1991-2020
median
Tropical
storms
Hurricanes Major
hurricanes
Average 122.1 - 14.4 7.2 3.2
Extremely active Above 159.6 Above 123% Not defined
Above-normal Above 126.1 Above 103% 16 or more 9 or more 5 or more
Near-normal 73-126.1 47% - 102% 10-15 5-8 2-4
Below-normal Below 73 Below 46% 9 or fewer 4 or fewer 0-1
Reference:[6]
Top 10 Atlantic hurricane seasons
Season TS HU MH ACE
1933 20 11 6 258.57
2005 28 15 7 250.13
1893 12 10 5 231.15
1926 11 8 6 229.56
1995 19 11 5 227.10
2004 15 9 6 226.88
2017 17 10 6 224.88
1950 16 11 6 211.28
1998 14 10 3 181.76
1887 19 11 2 181.26

### 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, likely because it was a Category 4 hurricane which lasted for 4 weeks. 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; Cindy had an ACE of just 1.5175 and Lorenzo had a lower ACE of only 1.475. The lowest ACE of a major hurricane (Category 3 or higher), was Hurricane Gerda in 1969, with an ACE of 5.3.[9] The following table shows those storms in the Atlantic basin from 1950–2019 that have attained over 50 points of ACE.[9]

Storm Year Peak classification ACE Duration
Hurricane Ivan 2004
Category 5 hurricane
70.4 23 days
Hurricane Irma 2017
Category 5 hurricane
64.9 13 days
Hurricane Isabel 2003
Category 5 hurricane
63.3 14 days
Hurricane Donna 1960
Category 4 hurricane
57.6 16 days
Hurricane Carrie 1957
Category 4 hurricane
55.8 21 days
Hurricane Inez 1966
Category 4 hurricane
54.6 21 days
Hurricane Luis 1995
Category 4 hurricane
53.5 16 days
Hurricane Allen 1980
Category 5 hurricane
52.3 12 days
Hurricane Esther 1961
Category 5 hurricane
52.2 18 days
Hurricane Matthew 2016
Category 5 hurricane
50.9 12 days

### Historical ACE in recorded Atlantic hurricane history

There is an undercount bias of tropical storms, hurricanes, and major hurricanes before the satellite era (prior to the mid–1960s), due to the difficulty in identifying storms.

Classification criteria

Extremely active
Above Normal
Near Normal
Below normal
Accumulated Cyclone Energy - Atlantic
Season ACE TS HU MH Classification
1851 36.24 6 3 1 Below normal
1852 73.28 5 5 1 Below normal
1853 76.49 8 4 2 Below normal
1854 31.00 5 3 1 Below normal
1855 18.12 5 4 1 Below normal
1856 48.94 6 4 2 Below normal
1857 46.84 4 3 0 Below normal
1858 44.79 6 6 0 Below normal
1859 55.73 8 7 1 Below normal
1860 62.06 7 6 1 Below normal
1861 49.71 8 6 0 Below normal
1862 46.03 6 3 0 Below normal
1863 50.35 9 5 0 Below normal
1864 26.55 5 3 0 Below normal
1865 49.13 7 3 0 Below normal
1866 83.65 7 6 1 Below normal
1867 59.97 9 7 1 Below normal
1868 34.65 4 3 0 Below normal
1869 51.02 10 7 1 Below normal
1870 87.8 11 10 2 Near normal
1871 88.39 8 6 2 Near normal
1872 65.38 5 4 0 Below normal
1873 69.47 5 3 2 Near normal
1874 47.05 7 4 0 Below normal
1875 72.48 6 5 1 Near normal
1876 56.05 5 4 2 Below normal
1877 73.36 8 3 1 Near normal
1878 180.85 12 10 2 Extremely active
1879 63.63 8 6 2 Below normal
1880 131.08 11 9 2 Near normal
1881 59.25 7 4 0 Below normal
1882 59.4675 6 4 2 Below normal
1883 66.7 4 3 2 Below normal
1884 72.06 4 4 1 Below normal
1885 58.3 8 6 0 Below normal
1886 166.165 12 10 4 Extremely active
1887 181.26 19 11 2 Extremely active
1888 84.945 9 6 2 Below normal
1889 104.0425 9 6 0 Below normal
1890 33.345 4 2 1 Below normal
1891 116.105 10 7 1 Near normal
1892 115.8375 9 5 0 Below normal
1893 231.1475 12 10 5 Extremely active
1894 135.42 7 5 4 Below normal
1895 68.765 6 2 0 Below normal
1896 136.0825 7 6 2 Below normal
1897 54.54 6 3 0 Below normal
1898 113.2375 11 5 1 Near normal
1899 151.025 10 5 2 Near normal
1900 83.345 7 3 2 Below normal
1901 98.975 13 6 0 Near normal
1902 32.65 5 3 0 Below normal
1903 102.07 10 7 1 Near normal
1904 30.345 6 4 0 Below normal
1905 28.3775 5 1 1 Below normal
1906 162.88 11 6 3 Extremely active
1907 13.06 5 0 0 Below normal
1908 95.11 10 6 1 Near normal
1909 93.34 12 6 4 Near normal
1910 63.9 5 3 1 Below normal
1911 34.2875 6 3 0 Below normal
1912 57.2625 7 4 1 Below normal
1913 35.595 6 4 0 Below normal
1914 2.53 1 0 0 Below normal
1915 130.095 6 5 3 Below normal
1916 144.0125 15 10 5 Above normal
1917 60.6675 4 2 2 Below normal
1918 39.8725 6 4 1 Below normal
1919 55.04 5 2 1 Below normal
1920 29.81 5 4 0 Below normal
1921 86.53 7 5 2 Below normal
1922 54.515 5 3 1 Below normal
1923 49.31 9 4 1 Below normal
1924 100.1875 11 5 2 Near normal
1925 7.2525 4 1 0 Below normal
1926 229.5575 11 8 6 Extremely active
1927 56.4775 8 4 1 Below normal
1928 83.475 6 4 1 Below normal
1929 48.0675 5 3 1 Below normal
1930 49.7725 3 2 2 Below normal
1931 47.835 13 3 1 Below normal
1932 169.6625 15 6 4 Extremely active
1933 258.57 20 11 6 Extremely active
1934 79.0675 13 7 1 Near normal
1935 106.2125 8 5 3 Near normal
1936 99.775 17 7 1 Near normal
1937 65.85 11 4 1 Below normal
1938 77.575 9 4 2 Below normal
1939 43.6825 6 3 1 Below normal
1940 67.79 9 6 0 Below normal
1941 51.765 6 4 3 Below normal
1942 62.485 11 4 1 Below normal
1943 94.01 10 5 2 Near normal
1944 104.4525 14 8 3 Near normal
1945 63.415 11 5 2 Below normal
1946 19.6125 7 3 0 Below normal
1947 88.49 10 5 2 Near normal
1948 94.9775 10 6 4 Near normal
1949 96.4475 16 7 2 Near normal
1950 211.2825 16 11 6 Extremely active
1951 126.325 12 8 3 Near normal
1952 69.08 11 5 2 Near normal
1953 98.5075 14 7 3 Near normal
1954 110.88 16 7 3 Near normal
1955 158.17 13 9 4 Above normal
1956 56.6725 12 4 1 Below normal
1957 78.6625 8 3 2 Below normal
1958 109.6925 12 7 3 Near normal
1959 77.1075 14 7 2 Near normal
1960 72.9 8 4 2 Near normal
1961 205.395 12 8 5 Extremely active
1962 35.5675 7 4 0 Below normal
1963 117.9325 10 7 3 Above normal
1964 169.7675 13 7 5 Extremely active
1965 84.33 10 4 1 Below normal
1966 145.2175 11 7 3 Above normal
1967 121.705 8 6 1 Below normal
1968 45.0725 8 5 0 Below normal
1969 165.7375 18 12 5 Extremely active
1970 40.18 11 5 2 Below normal
1971 96.5275 13 6 1 Near normal
1972 35.605 7 3 0 Below normal
1973 47.85 8 4 1 Below normal
1974 68.125 11 4 2 Near normal
1975 76.0625 9 6 3 Below normal
1976 84.1725 10 6 2 Near normal
1977 25.3175 6 5 1 Below normal
1978 63.2175 12 5 2 Below normal
1979 92.9175 9 6 2 Below normal
1980 148.9375 11 9 2 Near normal
1981 100.3275 12 7 3 Near normal
1982 31.5025 6 2 1 Below normal
1983 17.4025 4 3 1 Below normal
1984 84.295 13 5 1 Near normal
1985 87.9825 11 7 3 Near normal
1986 35.7925 6 4 0 Below normal
1987 34.36 7 3 1 Below normal
1988 102.9925 12 5 3 Near normal
1989 135.125 11 7 2 Near normal
1990 96.8025 14 8 1 Near normal
1991 35.5375 8 4 2 Below normal
1992 76.2225 7 4 1 Below normal
1993 38.665 8 4 1 Below normal
1994 32.02 7 3 0 Below normal
1995 227.1025 19 11 5 Extremely active
1996 166.1825 13 9 6 Extremely active
1997 40.9275 8 3 1 Below normal
1998 181.7675 14 10 3 Extremely active
1999 176.5275 12 8 5 Extremely active
2000 119.1425 15 8 3 Above normal
2001 110.32 15 9 4 Near normal
2002 67.9925 12 4 2 Near normal
2003 176.84 16 7 3 Extremely active
2004 226.88 15 9 6 Extremely active
2005 250.1275 28 15 7 Extremely active
2006 78.535 10 5 2 Near normal
2007 73.885 15 6 2 Near normal
2008 145.7175 16 8 5 Above normal
2009 52.58 9 3 2 Below normal
2010 165.4825 19 12 5 Extremely active
2011 126.3025 19 7 4 Above normal
2012 132.6325 19 10 2 Above normal
2013 36.12 14 2 0 Below normal
2014 66.725 8 6 2 Below normal
2015 62.685 11 4 2 Below normal
2016 141.2525 15 7 4 Above normal
2017 224.8775 17 10 6 Extremely active
2018 132.5825 15 8 2 Above normal
2019 132.2025 18 6 3 Above normal
2020 180.3725 30 14 7 Extremely active
2021 11.8725 5 1 0 Current season

## Eastern Pacific

Within the Eastern Pacific Ocean, the United States National Oceanic and Atmospheric Administration and others, use the ACE index of a season to classify the season into one of three categories.[10] These three categories are above-, near- and below-normal and are worked out using an approximate tercile partitioning of seasons based on the ACE index, number of tropical storms, hurricanes and major hurricanes over the 30 years between 1981 and 2010.[10]

Classification criteria
Category ACE Index % of 1981-2010
median
Tropical
storms
Hurricanes Major
hurricanes
Average 113.3 - 15.4 8.4 3.9
Above-normal Above 115 115% 17 or more 9 or more 5 or more
Near-normal 80-115 80% - 115% 16 or less 8 or less 4 or less
Below-normal Below 80 Below 80% Not defined
Reference:[10]
Top 10 Pacific hurricane seasons
Season TS HU MH ACE
2018 23 13 10 318
1992 27 16 10 295
2015 26 16 11 287
1990 21 16 6 245
1978 19 14 7 207
1983 21 12 8 206
1993 15 11 9 201
2014 22 16 9 199
1984 21 13 7 193
1985 24 13 8 192

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.[11]

The following table shows those storms in the Eastern and Central Pacific basins from 1971–2018 that have attained over 30 points of ACE.[12]

Storm Year Peak classification ACE Duration
Hurricane Fico 1978
Category 4 hurricane
62.8 20 days
Hurricane John 1994
Category 5 hurricane
54.0 19 days
Hurricane Kevin 1991
Category 4 hurricane
52.1 17 days
Hurricane Hector 2018
Category 4 hurricane
50.5 13 days
Hurricane Tina 1992
Category 4 hurricane
47.7 22 days
Hurricane Trudy 1990
Category 4 hurricane
45.8 16 days
Hurricane Lane 2018
Category 5 hurricane
44.2 13 days
Hurricane Dora 1999
Category 4 hurricane
41.4 13 days
Hurricane Jimena 2015
Category 4 hurricane
40.0 15 days
Hurricane Guillermo 1997
Category 5 hurricane
40.0 16 days
Hurricane Norbert 1984
Category 4 hurricane
39.6 12 days
Hurricane Norman 2018
Category 4 hurricane
36.6 12 days
Hurricane Celeste 1972
Category 4 hurricane
36.3 16 days
Hurricane Sergio 2018
Category 4 hurricane
35.5 13 days
Hurricane Lester 2016
Category 4 hurricane
35.4 14 days
Hurricane Olaf 2015
Category 4 hurricane
34.6 12 days
Hurricane Jimena 1991
Category 4 hurricane
34.5 12 days
Hurricane Doreen 1973
Category 4 hurricane
34.3 16 days
Hurricane Ioke 2006
Category 5 hurricane
34.2 7 days
Hurricane Marie 1990
Category 4 hurricane
33.1 14 days
Hurricane Orlene 1992
Category 4 hurricane
32.4 12 days
Hurricane Greg 1993
Category 4 hurricane
32.3 13 days
Hurricane Hilary 2011
Category 4 hurricane
31.2 9 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, 1971–2021

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 2020 season.[13] The 35 year median 1971–2005 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).

Above normal
Near normal
Below normal
Accumulated Cyclone Energy - Pacific
Season ACE TS HU MH Classification
1971 139 18 12 6 Above normal
1972 136 14 8 4 Above normal
1973 114 12 7 3 Near normal
1974 90 18 11 3 Near normal
1975 112 17 9 4 Near normal
1976 121 15 9 5 Above normal
1977 22 8 4 0 Below normal
1978 207 19 14 7 Above normal
1979 57 10 6 4 Below normal
1980 77 14 7 3 Below normal
1981 72 15 8 1 Below normal
1982 161 23 12 5 Above normal
1983 206 21 12 8 Above normal
1984 193 21 13 7 Above normal
1985 192 24 13 8 Above normal
1986 107 17 9 3 Near normal
1987 132 20 10 4 Above normal
1988 127 15 7 3 Above normal
1989 110 17 9 4 Near normal
1990 245 21 16 6 Above normal
1991 178 14 10 5 Above normal
1992 295 27 16 10 Above normal
1993 201 15 11 9 Above normal
1994 185 20 10 5 Above normal
1995 100 10 7 3 Near normal
1996 53 9 5 2 Below normal
1997 167 19 9 7 Above normal
1998 134 13 9 6 Above normal
1999 90 9 6 2 Near normal
2000 95 19 6 2 Near normal
2001 90 15 8 2 Near normal
2002 125 16 8 6 Above normal
2003 56 16 7 0 Below normal
2004 71 12 6 3 Below normal
2005 96 15 7 2 Near normal
2006 155 19 11 6 Above normal
2007 52 11 4 1 Below normal
2008 83 17 7 2 Near normal
2009 127 20 8 5 Above normal
2010 52 8 3 2 Below normal
2011 121 11 10 6 Above normal
2012 98 17 10 5 Near normal
2013 76 20 9 1 Below normal
2014 199 22 16 9 Above normal
2015 287 26 16 11 Above normal
2016 183 22 13 6 Above normal
2017 100 18 9 4 Near normal
2018 318 23 13 10 Above normal
2019 97 19 7 4 Near normal
2020 73 17 4 3 Below normal
2021 29 7 2 1 Current season

## North Indian

There are various agencies over the North Indian Ocean that monitor and forecast tropical cyclones, including the United States Joint Typhoon Warning Center, as well as the Bangladesh, Pakistan and India Meteorological Department.[4] As a result, the track and intensity of tropical cyclones differ from each other, and as a result, the accumulated cyclone energy also varies over the region.[4] However, the India Meteorological Department has been designated as the official Regional Specialised Meteorological Centre by the WMO for the region and has worked out the ACE for all cyclonic systems above 17 knots (31 km/h; 20 mph) based on their best track analysis which goes back to 1982.[4][14]

Top 10 North Indian Ocean cyclone seasons
Season D DD CS SCS VSCS ESCS SUCS ACE
2019 12 11 8 6 6 3 1 77.95
1989 10 6 3 2 1 1 1 45.54
2013 10 6 5 4 3 1 0 38.87
2018 14 9 7 5 3 1 0 35.61
2015 12 9 4 2 2 2 0 33.92
1999 10 8 5 3 3 2 1 33.60
2007 11 8 4 2 2 2 1 32.74
1982 19 11 8 5 4 3 0 30.04
1992 13 11 7 2 1 1 0 27.23
2010 8 6 5 4 2 1 0 26.90
References: [4][14]

## References

1. ^ Mark Saunders; Adam Lea (2007). "Summary of 2006 NW Pacific Typhoon Season and Verification of Authors' Seasonal Forecasts" (PDF). Tropical Storm Risk. Archived from the original (PDF) on 2007-11-29. Retrieved 2013-09-01.
2. ^ a b c Bell, Gerald D; Halpert, Michael S; Schnell, Russell C; Higgins, R. Wayne; Lawrimore, Jay; Kousky, Vernon E; Tinker, Richard; Thiaw, Wasila; Chelliah, Muthuvel; Artusa, Anthony (June 2000). "Climate Assessment for 1999". Bulletin of the American Meteorological Society. 81 (6): S19. doi:10.1175/1520-0477(2000)81[s1:CAF]2.0.CO;2.
3. ^ a b Gray, William Mason (May 26, 1988). "Forecast of Atlantic Seasonal Hurricane Activity for 1988" (PDF). Colorado State University: 13-14. Cite journal requires |journal= (help)
4. Mohapatra M; Vijay Kumar, V (March 2017). "Interannual variation of tropical cyclone energy metrics over North Indian Ocean". Climate Dynamics. 48 (5–6): 1431–1445. doi:10.1007/s00382-016-3150-3.
5. ^ "Weekly Tropical Climate Note July 14, 2020". Australian Bureau of Meteorology. July 14, 2020. Archived from the original on September 4, 2020. Retrieved September 4, 2020.
6. "Background information: North Atlantic Hurricane Season". United States Climate Prediction Center. May 22, 2019. Archived from the original on July 24, 2020. Retrieved August 22, 2020.
7. ^ "Accumulated Cyclone Energy of North Atlantic hurricanes". Our World in Data. Retrieved 15 February 2020.
8. ^ "Atlantic hurricane best track (HURDAT version 2)" (Database). United States National Hurricane Center. May 25, 2020.
9. ^ a b "Atlantic hurricanes by ACE - 1950-2012". Policlimate. Archived from the original on 10 August 2017. Retrieved 7 August 2017.
10. ^ a b c "Background information: Eastern Pacific Hurricane Season". United States Climate Prediction Center. May 22, 2019. Archived from the original on July 24, 2020. Retrieved August 22, 2020.
11. ^ "Eastern Pacific Best Track Data - (1949 - present)". National Hurricane Center. Retrieved 12 August 2018.
12. ^ Webb, Eric. "Hurricane Hector 2018 - Discussion". Twitter. Retrieved 12 August 2018.
13. ^ "East North Pacific ACE (through 30 Nov. 2005)". Archived from the original on 2006-09-20. Retrieved 2006-02-27.
14. ^ a b Tropical Cyclone Energy Matrix over North Indian Ocean (PDF) (Report). India Meteorological Department. 2020. Archived (PDF) from the original on July 18, 2020. Retrieved September 3, 2020.