CHENNAI:Even as the State government commenced preparatory works to deal with the forthcoming monsoon, India Meteorological Department (IMD) on Saturday released northeast monsoon (NEM) seasonal outlook for October to December according to which Tamil Nadu is likely to witness 12 per cent excess rainfall.
The NEM season is the major period of rainfall activity over the southern peninsula, particularly in the meteorological subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu-Puducherry.
For Tamil Nadu, this is the main rainy season accounting for about 48 per cent of annual rainfall. Coastal districts of the State get nearly 60 per cent of the annual rainfall and the interior districts get about 40-50 per cent of the annual rainfall.
S Balachandran, Deputy director general of meteorology, Regional Meteorological Centre, told Express that rainfall over Tamil Nadu is most likely to be above normal, i.e. equal to or above 112 per cent of long period average (LPA), which is 438.2 mm, during the period.
S Balachandran, deputy director general of meteorology, Regional Meteorological Centre, said it was indicative as NEM rainfall shows a high degree of variability of 27 per cent.The recent NEM seasons of 2015 and 2016 saw two extreme seasonal rainfall scenario. Whereas the NEM 2015 was +52 per cent over the Tamil Nadu sub division with some extremely heavy rainfall activity and unprecedented floods over the north coastal districts of Chennai, Kancheepuram and Thiruvallur. The NEM 2016 was the worst deficient at -62 per cent in the last 140 years. NEM 2017 under neutral conditions witnessed normal rainfall. The State had received 401 mm of rainfall between October and December as against normal rainfall of 442 mm, which is 9 per cent less. As per IMD, anything between -19 per cent to +19 per cent is considered normal.
Balachandran said NEM onset depends on how fast south-west monsoon (SWM) withdraws. SWM started withdrawing from the western parts of Rajasthan from Tuesday morning.As per the IMD all-India weather inference, the typical anticyclone that shows signs of the monsoon on retreat, has been established. Normal date of onset of the NEM is around October 20 with a deviation of about a week on either side. Last year, the onset was on October 25 and the monsoon became active only in the first week of November.