The India Met Department has announced the retreat of an eventful 2015 North-East monsoon from Tamil Nadu, Puducherry, Kerala and parts of Andhra Pradesh and Karnataka.

The season technically ended on December 31, but the Met seems to have waited out for specific meteorological patterns to fully settle down to signal the end of the season.

Bumper season

This included the shifting of the ‘inter-tropical convergence zone’ (ITCZ), the belt of convection (the process of cloud-building and precipitation) moving to the South of the Equator.

The ITCZ in turn tracks the movement of the Sun across the tropics between the northern and southern hemispheres to take the monsoon from place to place.

Currently, the monsoon is active over Australia coinciding with the summer in the southern hemisphere and will track back to the north by June to trigger year 2016 South-West monsoon for India.

Meanwhile, year 2015 delivered a bumper North-East monsoon for Tamil Nadu, Puducherry and Kerala after a rout of the preceding South-West monsoon.

Second best

Tamil Nadu received excess rain to the extent of 53 per cent above normal between October 1 and December 31 while Puducherry performed better with excess rainfall of 61 per cent.

Five districts in Tamil Nadu received excess rain above 100 per cent. These are Kancheepuram (183 per cent); Tiruvallur (149 per cent); Tirunelveli (125 per cent); Vellore (114 per cent); and Chennai (104 per cent).

An analysis of rainfall record the past 10 years shows that the year 2015 season (excess of 53 per cent) is second only to year 2005 (excess of 79 per cent).

Another notable feature about the season is the fact that the excess rainfall was delivered despite there being no cyclone or a major depression in the Bay of Bengal.

No cyclone

The two heavy rainfall events on November 15/16 and December 2 were triggered by well-marked low-pressure areas, which wind down in strength by at least two full rounds below a cyclone.

The fact that these comparatively weaker systems were able to dump some of the heaviest rainfall on record is attributed to the unmistakeable push from the strong El Nino in the Pacific, say Met experts.

Meanwhile, Kerala received 27 per cent excess rainfall and Lakshadweep, 65 per cent. Ernakulam district received the maximum rainfall (excess of 75 per cent) while Kannur and Pathanamthitta shared the second place with 53 per cent each.

Thiruvananthapuram received excess rain of 51 per cent but the two northern districts of Palakkad (-14 per cent) and Wayanad (-9 per cent) ended up with a deficit.

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