Chennai: The devastating rains that created havoc in Chennai and neighbouring districts earlier this month, was due to slow movement of weaker systems present over Bay of Bengal which subsequently led to 53 per cent higher rainfall than the average, the weather office said on Thursday.

"As the clouds above the sea were normal, the weaker systems like trough, low pressure moved slowly bringing copious rainfall," Regional Meteorological Centre Director S R Ramanan told reporters in Chennai.

He was giving a detailed analysis on the rainfall registered during the North East Monsoon that normally sets in during the October-December period for Tamil Nadu and neighbouring Puducherry. "On an average, Tamil Nadu and Puducherry receives 44 cm of rainfall during the North East Monsoon. This year the rainfall recorded is 68 cm in these three months, which is 53 per cent more," he said.

In 2013, rainfall received was 33 per cent less compared to average rainfall. In 2014, October received heavy rain but there was no rain in the next two months. "But, in 2015 the rainfall received in Tamil Nadu and Puducherry was very good and it was similar to 2005," he said.

Giving statistics, he said Kancheepuram district registered the heaviest rainfall -- 183 per cent higher at 181.5 cm as against average rainfall of 64 cm in October-December period.

Tiruvallur district recorded 146 cm compared to average 59 cm of rain while Chennai, which normally receives 79 cm of rainfall, recorded 160 cm, 104 per cent above average, he said.

To a query, he said if the weaker low pressure or trough moved towards Gulf of Mannar region, south interior districts would also have received "record rainfall". "Since the weaker systems were moving slowly or almost remained stationary, the coastal districts received heavy rainfall," he added.

Due to heavy rains earlier this month, Chennai and neigbouring districts were inundated. According to the government, 345 persons lost their lives in rain-related incidents during the period while many were rendered homeless. Asked if the North East Monsoon may be considered inactive following conclusion of the season from today, he said, "Even today Pechchiparai in Kanyakumari district received 4 mm of rainfall. But if there is no rainfall for four to five days, we may say the monsoon has ceased."

He said the formation of El Nino in Pacific Ocean, an abnormal weather pattern that causes warming of Pacific Ocean, was also one of the reasons that brought heavy rain in December in coastal districts.