The northeasterly winds have set in over Coastal Tamil Nadu and also over Coastal Andhra Pradesh and interiors of South Peninsula. The precondition for the onset of Northeast Monsoon has been met with for Chennai and rainfall is expected over the next 2 days for the capital city and suburbs. It may not be a pounding start to begin with and may pick up pace sometime next week.
The state of Tamil Nadu receives nearly 50% of annual rainfall during the Northeast Monsoon and the capital city averages 63% of rainfall during this period. A major share of these rains are experienced in October and November which have a monthly average of 316mm and 374mm respectively. The quantum of rainfall drops substantially to 177mm in December, aligned with the retreat of mini monsoon during the second half of the month.
The month of October has been disappointing this season as Meenambakkam has recorded just 1/3rd of normal and Nungambakkam measured 55% of average rainfall so far. These amounts are the lowest in the last 5 years with the best performance displayed in 2019 when both the observatories achieved normal rainfall. Many parts of the city are likely to receive the welcome showers of northeast monsoon over next 2 days and may recede thereafter.
There is a scare of prevailing La Nina conditions impacting monsoon rains. The past records are testimony of Pacific cooling spoiling the seasonal rainfall as it happened very recently in the year 2016. Also, the track records have enough evidence that any major shortfall incurred in the initial phase becomes difficult to cover up. Frequent Easterly Waves or repeated cyclonic circulations off Tamil Nadu coast in the Bay of Bengal are the only hopes for the road to recovery.