Why this is Important ? The period between October and December is considered favorable for the development of cyclones in the Bay of Bengal and the Arabian Sea. This year, however, October passed without formation of a cyclonic storm.
What is cyclone?
- A system of winds rotating inwards to an area of low pressure, with an anticlockwise (northern hemisphere) or clockwise (southern hemisphere) circulation; It is also an area of low depression.
- Factors like wind speed, wind direction, temperature and humidity contribute to the development of cyclones.
There are two types of cyclones:
- Tropical cyclones
This type of cyclone develop in the region between the Tropics of Capricorn and Tropic of Cancer. They are large-scale weather systems developing over tropical or subtropical waters, and at this place they get organized into surface wind circulation.
- Extra Tropical cyclones
This type of Cyclone occur in temperate zones and high latitude regions, though they are often known to originate in the Polar Regions. Also called Temperate cyclones or middle latitude cyclones or Frontal cyclones or Wave Cyclones.
When do cyclones form in India?
- About 80 cyclones are formed around the world annually, out of which five are formed in the Bay of Bengal and the Arabian Sea, together known as the North Indian Ocean.
- Cyclones in the North Indian Ocean occur during two seasons, April to June (pre-monsoon) and October to December (post-monsoon). May and November are the most conducive months for development of cyclones.
- Cyclonic disturbances are common in October; some of these develop into a cyclone.
- These disturbances enter the Bay of Bengal from the South China Sea side and head towards the Indian coast.
- Generally, the India Meteorological Department (IMD) describes the formation of one cyclone and two cyclonic disturbances in October as normal.
- This year, however, there was no system that intensified to form a cyclone.
- Although there were three cyclonic disturbances. Two of these disturbances caused widespread rain — one along Andhra Pradesh, Telangana, north Karnataka and Maharashtra, the other in West Bengal and Bangladesh.
How often do cyclones skip October?
Data on the frequency of cyclone development during 1891-2020 show that no cyclones formed in October on 42 occasions during these 130 calendar years. The longest period of absence of cyclones during October was between 1950 and 1954.
Why were there none this October?
- IMD officials have attributed it to weak La Niña conditions (a kind of weather pattern) along the equatorial Pacific Ocean, where cooler-than-normal sea surface temperatures have been prevailing since August.
- This has prevented low-pressure systems from intensifying beyond a deep depression.
- Also, high vertical wind shear (caused by significant wind speed differences between higher and lower atmospheric levels) prevented low-pressure systems and depressions from strengthening into a cyclone.
What is the forecast for November?
- Although November is one of the main months when cyclones develop, IMD officials note that at present there are no immediate weather systems likely to form in either sea.
- In addition, the Madden–Julian Oscillation (a tropical weather system) has just crossed the North Indian Ocean and moved eastwards; so there will be no supportive factors that could influence the formation of cyclones this month.
Worldwide Terminology of Tropical Cyclones
They are given many names in different regions of the world –
- Typhoons in the China Sea and Pacific Ocean
- Hurricanes in the West Indian islands in the Caribbean Sea and Atlantic Ocean
- Tornados in the Guinea lands of West Africa and southern USA.
- Willy-willies in north-western Australia
- Tropical Cyclones in the Indian Ocean.
The naming of cyclones over North Indian Ocean (Tropical Cyclone)
The names of cyclones in the Bay of Bengal, the Indian Ocean and the Arabian Sea are decided by eight countries (The countries that get to name the cyclones are India, Pakistan, Oman, Myanmar, Bangladesh, Maldives, Sri Lanka and Thailand)
- Each of them lists out eight names which are approved by the weathermen of these countries.
- So each time the list has 64 names.
- The countries take turns to name the cyclones.
- The first cyclone named by India was Agni, in 2004 and Vayu in 2019
Name of the cyclone in last two year (2019-20)
- Origin: Pabuk originated as a tropical disturbance in the South China Sea(Gulf of Thailand) on December 28, 2018,
- Origin: Fani originated from a tropical depression that formed west of Sumatra in the Indian Ocean on 26 April.
- Origin: Vayu originated from a low-pressure area that was first noted by the India Meteorological Department (IMD) on 9 June, near the northern Maldives. After consolidating into a depression, the storm tracked slowly north-northwestward over the eastern Arabian Sea, and reached cyclonic storm intensity late on 10 June.
- Origin: Arabian Sea
- Origin: Andaman Sea/ Bay of Bengal
- Origin: East-central Arabian Sea
- Origin: Arabian Sea
- Origin: Southwestern Arabian Sea, east of Somalia
- Amphan (pronounced Um-Pun)
- Origin: Very severe cyclone between the Sagar islands of West Bengal and the Hatiya islands of Bangladesh
- Origin – Cyclonic Storm formed over East central Arabian Sea. The name in the new list was suggested by Bangladesh.
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