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In the Indian Ocean north of the equator, tropical cyclones can form throughout the year on either side of India. On the east side is the Bay of Bengal, and on the west side is the Arabian Sea.
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Sub-basins
The Bay of Bengal, located in the northeast of the Indian Ocean, is responsible for the formation of some of the strongest and deadliest tropical cyclones in the world. The basin is abbreviated BOB by the India Meteorological Department (IMD), the official Regional Specialized Meteorological Center of the basin. The Bay of Bengal's coast is shared among India, Bangladesh, Myanmar, Sri Lanka and western part of Thailand. The strongest storm in the bay was the 1999 Odisha cyclone.
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), the official Regional Specialized Meteorological Centre (RSMC) of the basin. The Arabian Sea's coast is shared among India, Yemen, Oman, Iran, Pakistan, Sri Lanka, Maldives and Somalia. 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. During the winter, the winds are milder and blow in the opposite direction, from the northeast to the southwest. Cyclones are rare in the Arabian Sea, but the basin can produce strong tropical cyclones. Super Cyclonic Storm Gonu was the strongest recorded tropical cyclone in the basin. However, storms typically do not reach a high intensity in the Arabian Sea due to the small amount of water, dry air coming from the desert of the Arabian Peninsula, and unfavorable wind shear from the monsoon.
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. 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. These memoirs gave accounts and tracks of individual storms in the Bay of Bengal and the Arabian Sea.
During the 2004 post monsoon season the IMD started to name tropical cyclones, within the basin with the first one named Onil during September 2004.
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.
Water temperatures in the Arabian Sea are typically warm enough to allow for tropical cyclogenesis year round, although strong wind shear from the monsoon trough prevents formation in the summer months and limits intensity other times of the year. An increase in air pollution since the 1930s caused a decrease in the wind shear, allowing storms to have become stronger since 1979.