In the Indian Ocean north of the equator, tropical cyclones can form throughout the year on either side of the Indian subcontinent, although most frequently between April and June, and between October and December.

Cumulative track map of all North Indian Ocean cyclones from 1970 to 2005

The North Indian Ocean is the least active official basin, contributing only seven percent of the world's tropical cyclones. However the basin has produced some of the deadliest cyclones in the world, since they strike over very densely populated areas.[1] The Regional Specialized Meteorological Centre (RSMC) is the India Meteorological Department (IMD) and it is responsible to monitor the basin, issues warning and name the storms.[2]

Sub-basins

Thumb
Very severe cyclonic storms Luban (left) and Titli (right) over the Arabian Sea and the Bay of Bengal in October 2018

The basin is divided into two sub-basins   the Bay of Bengal and the Arabian Sea.[3]

The Bay of Bengal, located in the northeast of the Indian Ocean. The basin is abbreviated BOB by the India Meteorological Department (IMD).[4] The United States's Joint Typhoon Warning Center unofficially designates as B to classify storms formed in the Bay of Bengal.[5] The Bay of Bengal's coast is shared among India, Bangladesh, Myanmar, Sri Lanka and western part of Thailand.[6] This sub-basin is the most active and produces some of the deadliest cyclones of all time.[7] The most intense cyclone in the bay was the 1999 Odisha cyclone.[8]

The Arabian Sea is a sea located in the northwest of the Indian Ocean. Tropical cyclones in the basin are abbreviated ARB by the India Meteorological Department (IMD).[4] The United States's Joint Typhoon Warning Center unofficially designates as A to classify storms formed in the Arabian Sea.[9] The Arabian Sea's coast is shared among Pakistan, India, Yemen, Oman, UAE, Iran, Sri Lanka, Maldives and Somalia.[10] Monsoons are characteristic of the Arabian Sea and responsible for the yearly cycling of its waters. In summer, strong winds blow from the southwest to the northeast, bringing rain to the Indian subcontinent. Cyclones are less frequent in the Arabian Sea, but the basin can produce strong tropical cyclones.[10] Cyclone Gonu was the strongest and the costliest recorded tropical cyclone in the basin.[11]

History of the basin

The systematic scientific studies of tropical systems in the Bay of Bengal and Arabian Sea was started during the 19th century by Henry Piddington.[12] Piddington utilised meteorological logs of vessels that navigated the seas and published a series of memoirs, in the Journal of the Asiatic Society of Bengal between 1839 and 1858.[12] These memoirs gave accounts and tracks of individual storms in the Bay of Bengal and the Arabian Sea.[12]

During the 2004 post monsoon season the IMD started to name tropical cyclones within the basin, with the first one named Cyclone Onil during September 2004.[13] During 2015 a modification to the intensity scale took place, with the IMD and WMO calling a system with 3-minute maximum sustained wind speeds between 90 knots (165 km/h; 105 mph) and 120 knots (220 km/h; 140 mph) an extremely severe cyclonic storm.[14]

A study analysing the spring season of tropical cyclones in the Bay of Bengal found increases in both pre-monsoon precipitation and tropical cyclone intensity as a result of enhanced large-scale monsoon circulation after 1979. The deepened monsoon trough in the Bay of Bengal not only affects cyclone frequency and timing, but also acts to direct more cyclones towards Myanmar. Increased anthropogenic aerosols likely contributed to such a regional climate change.[15]

    Climatology

    Formation and frequency

    On average only five to six tropical cyclones form in the basin each year. Tropical cyclones form in the months of March to June and October to December, with peaks at May and November. Most of these storms form in the Bay of Bengal: either in the southeastern Bay of Bengal, in the Andaman Sea, or as a remnant of a typhoon from the South China Sea, and a few in the Arabian Sea.[8] High sea surface temperatures and humidity makes the bays more favourable to tropical cyclone development.[16] There are many tropical cyclones in the West Pacific; this may be another reason for increased[clarification needed] tropical cyclogenesis in the Bay, as it shares a fair portion of the increased quota of ACE. Meanwhile, the storms in the Arabian Sea mostly form over south-eastern part of the Arabian Sea or a remnant of a tropical cyclone from the Bay of Bengal, however the frequency of cyclogenesis in the Arabian Sea is generally less, due to cooler sea surface temperature and high wind shear.[8] However a strong positive Indian Ocean Dipole may cause an increase of tropical cyclogenesis than usual[clarification needed] which was seen in the 2019 season.[17] Very few tropical cyclones develop in the months of June to September (Monsoon months) because of high vertical wind shear. These storms form in the Bay of Bengal and peak as depressions or deep depressions before making landfall in Odisha or West Bengal. Another reason is the low life span in the sea[clarification needed] which also avoids the intensification of these low-pressure systems.[8]

    Movement

    Most of the storms move in a north-westerly direction and starts curving either towards southwest or northeast. There's a higher frequency of recurving towards northeast rather going southwest. In the Arabian Sea these storms mostly move in north-westerly direction targeting the Arabian Peninsula, however in some case these storm moves north-eastwards after crossing the 15°N latitude and strikes the Gujarati coast. In the Bay of Bengal, storms generally moves north-westwards until reaching the east coast and then moves north-eastwards.[18]

    Intensification

    Intensification probability is maximum in the months of April, May and November in case of a depression becoming a cyclonic storm and severe cyclonic storm. More than half of the depressions intensify into a storm and a quarter intensify into a cyclone in these months.[19]

    Landfall

    In the Arabian Sea, most storms dissipate offshore without making landfall, but a significant number of tropical cyclones also impact the west coast, particularly the states of Gujarat and Maharashtra. The remaining 11 percent makes landfall in either the Arabian Peninsula, Horn of Africa or Pakistan.[20] In rare cases, some storms make landfall in Iran, like Cyclone Gonu did in 2007.[21] Other than Gonu, two storms: Cyclone Yemyin and Kyarr made some or major impact in Iran.[22][23]

    In the Bay of Bengal, most of the storms strikes either the Indian states of Odisha or West Bengal and a significant number of storms hit the states of Andhra Pradesh and Tamil Nadu. 30 percent of the cyclones strike the countries of Bangladesh, Sri Lanka and Myanmar while the remaining 13 percent just dissipates off shore without making landfall.[20]

    Climate change

    After a series of devastating cyclones in 2018, rising number of cyclones in the Arabian Sea in 2019 and a rising trend of rapid intensification in 2020 and 2021, many climatologists agree that climate change have caused these activities. On average, five cyclonic storms occur every year in the Arabian Sea. However, in 2019 eight cyclonic storms formed, becoming the record highest number of tropical cyclones in the sub-basin, which was tied with the 1902 season.[24][25] Research has found that in recent decades the sea surface temperatures has risen up by 1.2–1.4 °C (2.2–2.5 °F) in the Arabian Sea.[25] During Cyclone Amphan’s rapid intensification, sea surface temperatures were as high as 33 °C (91 °F) in the Bay of Bengal, and parts of the Arabian Sea reached 32 °C (90 °F) before the formation of Cyclone Nisarga.[26] According to the Union Ministry of Earth and Science, the frequency of very severe cyclonic storms has risen up by one per decade in last two decades, despite the decrease of the overall tropical cyclone frequency in the same period.[25] Higher temperatures caused the cyclones to become more powerful and lead to tropical cyclone formation faster. Rising sea level also caused higher storm surge.[26] Researchers also predict that cyclones will be deadlier and stronger as the trend of warming sea surface temperatures continue. Rising sea levels also may cause severe flooding, strong storm surge and inundation of coastal towns.[26]

    Seasons

    Historical storm formation by month between 1990 and 2020
    10
    20
    30
    40
    50
    60
    Jan
    Feb
    Mar
    Apr
    May
    Jun
    Jul
    Aug
    Sep
    Oct
    Nov
    Dec
    •   Super Cyclone
    •   Extremely Severe
    •   Very Severe
    •   Severe
    •   Cyclonic Storm
    •   Deep Depression
    •   Depression

    Before 1890

    1890s

    More information Year, D ...
    YearDCSSCSNotes
    18901041
    18911343Total includes 1 Land Severe Cyclonic Storm
    18921272
    189312104
    18941260
    18951154
    18961083
    18971268
    18981373
    1899730
    Total 112 60 28
    References[27]
    Close

    1900s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    19001031
    1901632
    19021375
    19031482
    1904940
    19051060
    19061171
    19071584
    1908961
    190988 4
    Total 105 60 20
    References[27]
    Close

    1910s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    1910652
    1911754
    1912962
    19131062
    1914842
    1915960
    19161485
    19171031
    19181150
    19191163
    Total 95 54 21
    References[27]
    Close

    1920s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    1920950
    19211041
    19221366
    19231643
    19241360
    19252073
    192613103
    19271872
    19281370
    19291560
    Total 140 62 18
    References[27]
    Close

    Thy&_99 Nam=^ sunao kuch

    1930s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    193014101
    19311151
    19321462
    19331683
    19341650
    19351562
    19361863 VSCS Two293$75,000
    19371962
    19381044
    19391973
    Total 152 63 21
    References[27][28]
    Close

    1940s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    19401685
    19411984
    19421452
    19431471
    19441982
    19451532
    19461751
    19471842
    19481863
    19491211
    Total 162 55 23
    References[27]
    Close

    1950s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    19501640 SCS  SixteenUnknownUnknown
    19511542 SCS  FifteenUnknownUnknown
    19521742
    19531011
    19541410
    19551362
    19561442
    1957742
    19581252
    19591663
    Total 134 39 16 Unknown Unknown
    References[27]
    Close

    1960s

    Thumb
    This ESSA 3 satellite image was taken on November 3, 1966, at 0819 UTC of a tropical cyclone striking Madras, India
    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    19601553 VSCS  Ten20,299>$9.4 millionVast majority of the fatalities resulted from two cyclones striking East Pakistan three weeks apart
    19611854 SCS  Winnie11,525UnknownThree land depressions developed this season
    19621353 VSCS  Twelve769$34.5 millionDeadliest storm, Harriet, crossed over from the Western Pacific
    19631764 SuCS  Three11,735Unknown
    19641675 SuCS  "Rameswaram">1,827>$150 million
    19651464
    19661886
    19671564
    19681374 SuCS  "Burma"
    19691461 ESCS  Twelve
    Total 153 61 38 Three >47,000 >$193.9 million
    References[27]
    Close

    1970s

    More information Year, D ...
    YearDCSSCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    19701573 ESCS  "Bhola"300,000-500,00086.4 millionThe Bhola cyclone is the deadliest tropical cyclone recorded worldwide
    19711576 ESCS  "Odisha"
    19721876 ESCS  09B
    19731663 SCS  14B
    19741273 VSCS  06B
    19752074 ESCS  02A
    197614107 ESCS  02A
    19771855 SuCS  "Andhra Pradesh"up to 50,000$192 millionDevastated Krishna Delta area in Andhra Pradesh
    19781453 SuCS  "Sri Lanka"1,000+
    19791154 ESCS  01B
    Total 153 66 44 "Andhra Pradesh" >800,000 >$278.4 million
    References[27]
    Close

    1980s

    More information Year, D ...
    YearDDDCSSCSVSCSESCSSuCSStrongest
    storm
    DeathsDamages
    (USD)
    Notes
    1980141450000  CS  BOB 02
    1981121253300  VSCS  BOB 03
    1982191185330  ESCS  BOB 01
    19837421110  CS  Herbert
    19847743 3 2 0  ESCS  "Sriharikota"430
    1985151561 1 0 0  VSCS  "Bangladesh"11,107
    19868310 0 0 0  CS  02B11
    19879853 1 0 0  VSCS  01B
    19889553 2 2 0  ESCS  "Bangladesh"6,740$13 million
    198910532111 SuCS  Gay1,785$25.27 millionTyphoon Gay crossed over from the West Pacific Basin
    Total 110 84 44 21 15 9 1 Gay / Kavali >20,073 >$38.27 billion
    References[27]
    Close

    1990s

    Thumb
    The 1999 Odisha Cyclone making landfall over Odisha in 1999.
    More information Year, D ...
    YearDDDCSSCSVSCSESCSSuCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes and References
    199011622111 SuCS  BOB 01967$600 million[29][30]
    19919431111 SuCS  "Bangladesh">138,000$1.5 billion[30]
    1992131172110 ESCS  Forrest189$69 millionForrest crossed over from the West Pacific Basin
    19935422200 ESCS  BOB 02714$216 million
    19945542210 ESCS  "Bangladesh"315$12.5 million
    19958632210 ESCS  BOB 07554$46.3 million
    199610864200 VSCS  "Andhra Pradesh"2,075$1.9 billion
    19979732110 ESCS  "Bangladesh"117Unknown
    1998131065310 ESCS  "Gujarat">10,212$3 billion
    199910853321 SuCS  "Odisha"15,780$5 billionThe Odisha cyclone is the strongest cyclone recorded in the Northern Indian Ocean.
    Total 93 69 41 25 18 9 3 "Odisha" >168,923 ~$12.35 billion
    References[27]
    Close

    2000s

    Thumb
    Cyclone Gonu at its peak in 2007.
    More information Year, D ...
    YearDDDCSSCSVSCSESCSSuCSStrongest
    storm
    DeathsDamage
    (USD)
    Notes
    20007652220 ESCS  "South India"238$185 million
    20016541110 ESCS  "Gujarat"108$104 million
    20027741000 SCS  "West Bengal"182$25 million
    20037533100 VSCS  "Sri Lanka"358$163 million
    200410744110 ESCS  "Myanmar"587$130 million
    200512730000 CS  Pyarr273$21.4 million
    200612632110 ESCS  Mala623$6.7 million
    200711842221 SuCS  Gonu16,248$6.4 billion
    200810741110 ESCS  Nargis>138,927$15.4 billionThe deadliest cyclone season since 1970
    Second-costliest cyclone season on record
    20098641000 SCS  Aila421$618 million
    Total 90 64 38 17 9 8 1 Gonu >157,965 $16.65 billion
    References[27]
    Close

    2010s

    Thumb
    Cyclone Kyarr was the first super cyclone since 2007.
    More information Year, D ...
    YearDDDCSSCSVSCSESCSSuCSStrongest
    storm
    DeathsDamages
    (USD)
    Notes
    20108654210 ESCS  Giri402$2.99 billionThe most active season since 1998
    201110621100 VSCS  Thane360$277 million
    20125520000 CS  Nilam128$56.7 millionThe first depression of the year did not develop until October 10
    201310654310 ESCS  Phailin323$1.5 billionFeatured Phailin, the first Category 5-equivalent cyclone since Sidr in 2007
    20148532220 ESCS  Nilofar183$3.4 billion
    201512942220 ESCS  Chapala363$358 millionFirst season on record with two cyclones producing hurricane-force winds in Socotra
    201610541100 VSCS  Vardah401$5.4 billion
    201710632100 VSCS  Ockhi834$3.65 billion
    201814975310 ESCS  Mekunu343$4.33 billionThe most active season since 1992
    2019121186631 SuCS  Kyarr173$11.5 billionEarliest cyclonic storm in the basin
    First Super Cyclonic Storm since 2007
    Total 99 68 43 27 21 10 1 Kyarr 3510 $33.5 billion
    References[27]
    Close

    2020s

    Thumb
    Amphan was the costliest cyclone in the basin to strike land.
    More information Year, D ...
    YearDDDCSSCSVSCSESCSSuCSStrongest
    storm
    DeathsDamages
    (USD)
    Notes
    20209654311 SuCS  Amphan269$15.8 billionFirst super cyclonic storm in the Bay of Bengal since 1999
    Featured the costliest cyclone ever recorded in the basin, Amphan
    Costliest North Indian cyclone season on record
    202110653210 ESCS  Tauktae230$5.31 billion
    202215732000 SCS  Asani79$52.4 million

    First season on record to have two depressions forming in the month of March

    202310875430 ESCS Mocha523$1.07 billionMocha was one of the strongest cyclones ever formed in the basin's history.
    2024 1 1 1 1 0 0 0  SCS  Remal 113 None
    Total44272015951Amphan1214$21.163 billion
    Close

    Records

    See also

    Notes

      References

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