The June-September rainfall is expected to be 99 per cent of the long-term average, Deshmukh told a press conference here.
India's chief monsoon forecaster D Sivananda Pai, however, said that there was possibility of El Nino weather conditions developing in the central equatorial Pacific Ocean, which are usually associated with weak rainfall.
Summer monsoon rains are crucial for India as more than 60 per cent of the country's agriculture is dependent on good rainfall for a bumper harvest.
"Southwest monsoon seasonal rainfall for the country as a whole is most likely to be normal with the probability of 47 per cent," Deshmukh said.
An analysis of five predictors for the long-range forecast indicates 24 per cent probability for a below normal rainfall, he said.
However, the probability of season rainfall to be deficient or excess is less than 10 per cent, which is relatively low, Deshmukh said. PTI SKU