Northeast monsoon seems to be in a 'good' cycle for the state of Tamil Nadu. Last three seasons have performed normal or above normal and the current season looks to be on same track. Monsoon 2021 was the wettest over last one decade and measured a huge surplus of 59% rainfall. Northeast monsoon made an onset on 29th October this year, albeit on a feverish note. Weather activity has picked up in the last 3 days and few parts, including the state capital, have observed heavy showers. South Tamil Nadu has received heavy downpour at few places last night. Parangipettai and Thanjavur recorded 116mm and 124mm rainfall in the past 24hr.
Post monsoon from October to December is the chief rainy season for the state of Tamil Nadu. During southwest monsoon, the state receives 35% of annual rainfall (317.2mm) over a period of 4 months. Northeast monsoon season from October to December accounts for 48% of annual rainfall with a sharp peak in November. Degree of variability remains very high for the state with 27% coefficient of variation. Accordingly, the range of normal rainfall also, has a large swing between 88% and 112% of LPA.
Onset date of northeast monsoon over south peninsula and complete withdrawal of southwest monsoon from the country are consequential for quantum of rainfall during winter monsoon season. Invariably, southwest monsoon is commencing withdrawal later than normal and getting extended beyond mid October over the country.
The onset of Northeast Monsoon is getting pushed to the fag end of October and many a times nearly coincides with the exit of summer monsoon. This changing cycle is responsible for extreme variability in the behaviour of northeast monsoon, more so, for the state of Tamil Nadu.