"Southwest monsoon onset over Kerala is likely to be on June 3," Chief Monsoon Forecaster, India Meteorological Department (IMD), D Sivananda Pai told PTI in New Delhi.
Mr Pai admitted that it was a slight delay than the usual onset date of June 1.
The delay could be attributed to cyclone Mahasen that is churning the Bay of Bengal packing wind speed of 90 kmph. It is expected to make landfall near Chittagong coast in Bangladesh tomorrow night.
"Cyclonic activity weakens monsoon flow. It takes some time to reorganise," Mr Pai said when asked about reasons for the delay in onset over Kerala.
While Mahasen is expected to delay rains over Kerala, the strong cyclonic winds are driving monsoon flow over Andamans where the onset is expected by Friday.
"This year, under the influence of tropical cyclone 'Mahasen', which is currently located over the central Bay of Bengal, low level cross equatorial monsoon flow has appeared over south Andaman Sea and adjoining south Bay of Bengal," the weather office said.
Andaman and Nicobar Islands usually receive monsoon showers between May 10 and May 20.
Last month, the weather office had forecast normal monsoon this year with overall rainfall expected to be 98 per cent of the long period average.
Monsoon is crucial for the kharif crops such as rice, soyabean, cotton and maize because almost 60 per cent of the farm land in the country is dependent on rains.