In the Gowarikar model, nationwide rainfall within the range of +/- 10 per cent of the long period average was termed as “normal rainfall”. In the models used in the last four years, nationwide rainfall within the range of 98 to 102 per cent of the average was termed “near normal”. The 4-month south-west monsoon season begins in June and the IMD will make a forecast in mid-May on the date of approach of the monsoon over the Kerala coast. “In the last week of June, we will make a forecast for the nationwide rainfall in July, a final forecast for the monsoon period and rainfall forecast over four homogeneous region,” said IMD director M Rajeevan.

According to Rajeevan, most parameters used in the forecast model were old, except one — the North Atlantic mean sea level pressure in May. The parameters have been selected to suit the changed scenario. The Ministry’s annual report, admitting the impact of climate change, said: “The findings indicate minor but perceptible shifts in the monsoon trough positions and strength of monsoon flow.”