Chennai received 5 cm rain - five times more than normal - on December 1, the worst day of flooding in the city (Agence France-Presse photo)
Chennai had been warned by the Met department in mid-October this year that it could see very heavy rainfall of the kind that could cause flooding.
The India Meteorological Department or IMD had, on October 16, forecast a very wet last quarter, saying that the seasonal rainfall was likely to be more than 112 per cent of the long period average for Tamil Nadu, which it assessed at 43.82 centimetres.
Any forecast of over 10 per cent extra rainfall over the normal is considered flooding.
The "forecast outlook for 2015 North East Monsoon Season" was issued almost a month before unprecedented rains first lashed Chennai and adjoining areas, causing floods that seem to have caught the local authorities totally off-guard.
"I am only a meteorologist and not a town planner," said IMD Director General LS Rathore, confirming that the weather office had indeed warned that there could be excess rain which could cause flooding.
Mr Rathore said the region is "super-saturated" with water, with rain in catchments flowing down to the sea along the rivers, causing the floods in Chennai.
Experts say town planners should follow up such forecasts by de-silting drains, cleaning storm water drains, ensuring there are no encroachments and putting in place emergency plans for communications and essential supplies.
On December 2nd, the worst day of flooding in Chennai, the city received 34.5 cm of rainfall. The highest rainfall in a single day in Chennai was 45.2 cm on November 25, 1976, but that did not cause flooding as this was before hyper construction activity began on flood plains. The city's natural sponges had absorbed the deluge then.
The October forecast was based on 2015 being an El Nino year, when oceans warm up, resulting in excessive moisture being lifted up by the winds and coming down as heavy rain of the kind being experienced by Chennai and its adjoining regions.
M Rajeevan, Director of the Indian Institute of Tropical Meteorology in Pune said the excess rain was more or less on expected lines and trying to link it to climate change or global warming "may not be correct."