"Conditions are favourable for the onset of southwest monsoon over Kerala and its further advance into some more parts of south Arabian sea, remaining parts of Maldives- Comorin area, some parts of Tamil Nadu and some more parts of Bay of Bengal during the next 48 hours.
"Conditions are also favourable for advance of southwest monsoon into some parts of northeastern states during the next 72 hours," said a statement by the Indian Meteorological Department.
The Met department forecast states the monsoon is expected to hit Kerala by June 5.
Thunderstorm has been observed over Odisha, Assam, Konkan and Goa, coastal Karnataka and south Kerala, the department said.
After four years of normal and above-normal monsoon, India is expected to have below normal monsoon this year with rainfall projected to be 95 per cent, which is disappointing for the farming community.
Officials in the weather department said the monsoon is expected to be below normal because of El-Nino effect, which is generally associated with the warming of ocean water.
"Lead indicators point to continuing sluggishness in domestic economic activity in the first quarter of 2014-15.
The outlook for agriculture is clouded by the meteorological department's forecasts of a delay in the onset of the south-west monsoon with a 60 per cent chance of the occurrence of El Nino," RBI Governor Raghuram Rajan said in a second bi-monthly monetary policy statement on Tuesday.