CHENNAI: The Regional Meteorological Centre on Wednesday said the conditions have become favourable for the onset of northeast monsoon rains from October 29. It’s a delayed start for the monsoon, which normally commences around October 20.
The Met department said with the likely onset of northeasterly winds in the lower tropospheric levels over the Bay of Bengal and South Peninsular India, monsoon rains are likely to commence over Southeast Peninsular India from around October 29.
A cyclonic circulation lies over westcentral and adjoining southwest Bay of Bengal in lower tropospheric levels and a trough runs from south interior Karnataka to southwest Bay of Bengal across Tamil Nadu in lower tropospheric levels. Under the influence of the two systems, scattered to fairly widespread light/moderate rain with isolated heavy rains and thunderstorm/lightning is very likely over Tamil Nadu, Puducherry and Karaikal on October 29 and 30.
Director, Area Cyclone Warning Centre at the Regional Meteorological Centre, P Senthamarai Kannan, told TNIE: “As southwest monsoon has withdrawn completely last week itself, we can’t declare commencement of northeast monsoon rains until fairly widespread rains are reported in majority of weather stations in coastal Tamil Nadu. We expect rains to start from October 28to 29.”
As per the forecast, heavy rain is likely in 20 districts including Chengalpet, Villupuram, Cuddalore, Mayiladuthurai, Nagapattinam, Tiruvarur, Thanjavur, Tiruchirappalli, Ariyalur, and Perambalur on October 29. On October 30, nearly 27 districts are likely to get heavy rain.Kannan attributed the delay in onset of monsoon to the cyclonic storm that formed in the Bay of Bengal and made its landfall in Bangladesh.
The IMD officials said the NE monsoon rains will be normal over the south Peninsular India consisting of five meteorological subdivisions (Tamil Nadu, Pondicherry, Coastal Andhra Pradesh, Rayalaseema, Kerala and South Interior Karnataka) in the range of 88%-112% of Long Period Average (LPA). The LPA of rainfall over south peninsular India during the October to December season based on data from 1971 to 2020 is about 334.13 mm.
Besides the rain, the NEM is notorious for tropical cyclones. On an average, the season witnesses three cyclonic storms but this year there is a likelihood of more and also intense storms forming in Bay of Bengal due to prevailing La Nina and negative Indian Ocean Dipole (IOD) conditions.
Last year, the NE monsoon rains commenced on October 25. Excepting coastal Andhra Pradesh that received normal rainfall during the season, the other four subdivisions received excess to large excess rainfall with Kerala, south interior Karnataka and Rayalaseema recording more than 100% excess rainfall.