The monsoon is vital for India as half of its farmland lacks irrigation. To cut dependence on rains, India plans to expand its farmland under irrigation by at least a tenth by 2017.
Agriculture accounts for 14 percent of Asia's third-largest economy but employs more than half of the workforce. Healthy harvests can help keep a lid on food price inflation, which has been stuck at around 9 percent.
Rainfall is expected to be 95 percent of the long-term average, with a margin for error of plus or minus 5 percent, during the June-to-September season, the weather office said in a statement.
The Meteorological Department defines average, or normal, rainfall as between 96 percent and 104 percent of a 50-year average of 89 cm for the entire season.
The first official monsoon forecast is in line with the latest outlook of the Geneva-based World Meteorological Organisation's (WMO) forum that predicted mostly below-average rains in much of South Asia including India.
"El Nino condition continues to be neutral in the pacific but the probability of its occurrence is on the higher side; about 60 percent," said a weather office official.
The last time India faced a drought with rainfall below the normal range was in 2009 and prior to that, in 2004 and 2002 - with El Nino hitting the Indian monsoon season on each occasion.
A strong El Nino, marked by a warming of the sea surface on the Pacific Ocean, can cause severe drought in Australia, Southeast Asia and India, while drenching other parts of the world such as the U.S. Midwest and Brazil with rain.
In 2013, the Indian monsoon posted 106 percent rains, qualifying as an above average year for rainfall, resulting in record grains production at 262 million tonnes for the 2013/14 crop from July.
India will update its forecast in June, after the southwest monsoon has typically engulfed half of the country.