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.