This northeast monsoon seems to be on its way to create new records for the State.
While the previous spells ravaged Cuddalore and Puducherry, the north coastal districts of Chennai, Tiruvallur and Kancheepuram were the most affected by this week’s (on Tuesday) torrential downpour.
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Though there is nearly a month for the monsoon to wind up over the region, the State has already registered 53 cm of rainfall against its average of 44 cm. Chennai’s rainfall missed the record of wettest November of the century by 39.1 mm.
The all-time record of heavy downpour was 1,088.4 mm in November 1918. Tuesday’s incessant rain brought nearly 15 cm over Chennai inching closer to decade’s highest rainfall of 23 cm received on December 3, 2005.
Several weather stations in Chennai, Tiruvallur and Kancheepuram districts received very heavy rainfall to extremely heavy rainfall as in Chembarambakkam that recorded 25 cm in less than 10 hours.
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Weather experts observe that even a trough of low pressure or low-pressure area can influence such huge volume of rains with a potential of deluge.
Unlike a deep depression or cyclone that may cross the coast in a day or two, these weather systems that persists in the same area over the sea can impact cloud bursts and intense rains. Moreover, there was not much lull in northeast monsoon activity this year when the State gets respite with long dry spells. This indicates the volatile nature of the monsoon.
El Nino year
While 2015 is a strong El Nino year favouring northeast monsoon, it is not the only contributing factor that brought downpour over the State.
A complex interplay of global weather factors such as southern oscillation and Siberian High are also responsible for the heavy spells, notes Y.E.A. Raj, former deputy director general of meteorology, Chennai.
There were years when the State received excess rainfall even without El Nino. The year 2005 presents a classic example with 79 per cent of surplus rains.