Nor'westers

Nor'westers or the Kalbaishakhi ( bn, কাল বৈশাখী) ( or, କାଳ ବୈଶାଖୀ), Bordoisila as known in Assam, are localised rainfall and thunderstorm event which occurs in Bangladesh and Indian states of Bihar, Jharkhand, Odisha, Tripura and West Bengal often exceeding . These storms generally occur in afternoon or just before sunset, when thick dark black clouds start appearing over the sky and then bring gale-speed wind with torrential rain, often with hail, but spanning only a short period of time.

Etymology

In Bengali, Kalbaishakhi ( bn, কালবৈশাখী) means "fateful thing" which occurs in the Bengali month of Baishakh. It is also widely known as nor'westers in English and used in English newspaper since these storm travels from northwest to southeast. In Assam, it is known as Bordoisila which was derived from the Bodo word "Bardoisikhla", in which 'Bar' means wind, 'Dol' means water and 'Sikhla' means girl, represents the goddess of nature, wind and rain and also marks the beginning of the Assamese month Bohag or Baishagu.

Genesis

Kalbaishakhi, usually forms from April till the monsoon establishes itself over North-East India. However, in some occasion these storms can form in March. Based on event descriptions and the meteorological environments involved, these storms can be classified as progressive derechos. These storms originates over the Chhotanagpur Plateau between the states of Bihar and Jharkhand. It strengthens gradually, moves south-eastwards and affects the states of Odisha, West Bengal and Assam with gale-speed wind, torrential rains and hailstorms. In some occasion, incursion of moist air in these elevated places, amidst high temperature causes violent thunderstorms. Tornadoes also rarely form if there's enough moisture, convection and heat in the Ganga-Brahmaputra delta such as a tornado hit in Bangladesh's Manikganj district of Dhaka division which became the deadliest tornado in the history.

Effects

Kalbaishakhi brings destruction by uprooting trees due to gale-winds and waterlogging roads due to heavy rainfall. It often damages crop by hailstorms. However it is extremely helpful for kharif crops like jute, paddy, etc. and give relief after the mid-day heat and give rainfall to the dry soils for the development of the crops.

Due to global warming these storms are becoming infrequent and becoming stronger and stronger day by day, causing more destruction.

In Bengali literature

Many Bengali poets and artist have been inspired from Kalbaishakhi not just terror and fury but by its astounding beauty. Bengali poet Mohit Lal Majumder described the storm in his poem "Kalbaisakhi" and Rabindranath Tagore also got inspired from the storm and wrote a poem "Esho e Baisakh".

References

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Weather hazards
Climate of Asia