Cyclone Ockhi

Very Severe Cyclonic Storm Ockhi
Very severe cyclonic storm (IMD scale)
Category 3 (Saffir–Simpson scale)
Ockhi 2017-12-02 Suomi NPP.jpg
Cyclone Ockhi near peak intensity in the Arabian Sea on December 2
FormedNovember 29, 2017
DissipatedDecember 6, 2017
Highest winds3-minute sustained: 155 km/h (100 mph)
1-minute sustained: 185 km/h (115 mph)
Lowest pressure976 hPa (mbar); 28.82 inHg
Fatalities245 total, 661 missing
Damage> $5.07 billion (2018 USD)
Areas affectedSri Lanka, India, and Maldives
Part of the 2017 North Indian Ocean cyclone season

Very Severe Cyclonic Storm Ockhi[nb 1] was a strong tropical cyclone that devastated parts of Sri Lanka and India, and was the most intense tropical cyclone in the Arabian Sea since Cyclone Megh in 2015. The third and the strongest Cyclonic Storm of the 2017 North Indian Ocean cyclone season, the origins of Ockhi can be traced back to an area of low pressure that formed in the eastern Andaman Sea on November 21.[2][3] While traversing the southern part of the Bay of Bengal, favorable conditions enabled the system to consolidate into a deep depression. As a deep depression, it caused damage to property and life in Sri Lanka on November 29.[3] Due to high atmospheric moisture and warmer temperatures seas surface between Sri Lanka and Kanyakumari (Cape Comorin) in mainland India, Ockhi intensified into a Cyclonic Storm on November 30.[3]

While near Kanyakumari in mainland India, Cyclone Ockhi changed its path and headed towards Lakshadweep in the Arabian Sea, while intensifying.[4] Although the cyclone headed away from the coast of mainland India, it caused severe damages to structures and property and also claiming the lives of at least 218 people in the Southern parts of Tamilnadu and Kerala in India.[5][6][3] Ockhi impacted Lakshadweep on December 2. The cyclone uprooted coconut trees and caused extensive damages to houses, power lines and other infrastructure in the islands.[7] Ockhi dissipated near the south coast of Gujarat in India on December 6, due to prevailing conditions, even before entering the coast.[8]

Cyclone Ockhi originated from a low pressure area over southwest Bay of Bengal and adjoining areas of south Sri Lanka & equatorial Indian Ocean on 28 November. It crossed south coast of Gujarat between Surat and Dahanu as a well-marked low-pressure area on December 6. The storm traversed a distance of 2,538 km.[2] In its entire course, Cyclone Ockhi left a trail of massive destruction in Sri Lanka, Lakshadweep, South India, and Maldives as it strengthened from a depression to a mature cyclone. Though it rapidly weakened in its final stages over the Arabian Sea, it caused heavy rainfall along the western coast of India, particularly in Maharashtra and Gujarat. More than 245 fatalities were caused by Ockhi, including 218 in India[5] and 27 in Sri Lanka,[9] and it left at least 551 people missing, mainly fishermen.[10]

Meteorological history

Map plotting the track and intensity of the storm, according to the Saffir–Simpson scale

During November 28, an area of low pressure developed about 425 km (265 mi) to the south-southeast of Colombo, Sri Lanka.[2][11] The disturbance was located within an area of warm sea surface temperatures and moderate to strong vertical wind shear, it was also poorly organized, with atmospheric convection scattered around the disturbance's ill-defined low-level circulation center.[11] On November 29, the storm organized into a depression just off the southeastern coast of Sri Lanka, and the India Meteorological Department gave the system the identifier BOB 07.[12] Due to the storm's rapidly consolidating low level circulation center, the Joint Typhoon Warning Center issued a Tropical Cyclone Formation Alert on the system, shortly before classifying it as Tropical Cyclone 03B on November 29.[13] The IMD followed suit, upgrading the storm to a Deep Depression, and soon afterwards to Cyclonic Storm Ockhi. The storm tracked along Sri Lanka's southwestern and western coastline, towards the west-northwest, around the southern verge of a subtropical ridge located over India.[14] Owing to highly favorable conditions, the storm displayed a thick convective ring, surrounding a well-defined eye feature on the same day.[15] The storm tracked westwards and intensified further into a Severe Cyclone Storm, early on December 1.[16] Soon afterwards, Ockhi intensified further into a Very Severe Cyclonic Storm.[17]

Cyclone Ockhi undergoing extratropical transition off the Gujarat coast on December 4

As Ockhi moved further into the Arabian Sea, it travel through an area of sea surface temperatures of 31 °C (89 °F) and decreasing wind shear; a 23 mi (37 km) eye became visible on satellite imagery, prompting the JTWC to upgrade it to a Category 3-equivalent cyclone early on December 2.[18] On December 4, analysis showed that Ockhi was maintaining a source aloft, but there was restricted outflow on the western edge, due to a deepening trough advancing rapidly from the west.[19] Increasing vertical wind shear along with a deep layered subtropical ridge to the east steered it to north-northeast, and dry air intrusion from the west gradually weakened the system.[20] On the following day, the storm quickly became disorganized as it encountered increasingly unfavorable conditions, including high wind shear. As Ockhi became embedded within a deep mid-latitude trough, the storm rapidly underwent an extratropical transition.[21] Dry and cold air from the subcontinent rapidly weakened the storm, and it was last noted as a well-marked low-pressure area over the Gulf of Cambay on December 6.[22]

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