The southwest monsoon on Tuesday advanced into parts of the southern Bay of Bengal, the southern Andaman Sea, the Nicobar Islands and some parts of the North Andaman Sea, said the India Meteorological Department.

The weather agency added that conditions were favourable for it to further advance over some parts of South Arabian Sea, the Maldives and Comorin areas, some more parts of the South Bay of Bengal, entire Andaman and Nicobar Islands, remaining parts of Andaman Sea and some parts of central Bay of Bengal during the next three to four days.

The southwest monsoon season generally begins in June and starts to retreat by September.

The India Meteorological Department declares the onset of the season when it hits Kerala.

While the normal onset date of the season is June 1, it is expected to advance over Kerala about five days earlier this year, The Indian Express reported.

On April 15, the India Meteorological Department said that rainfall during the southwest monsoon season this year was likely to be above normal.

It added that the country was expected to get 105% of the long-period average rainfall, which refers to the mean rainfall during the four-month monsoon season over the last 50 years.

As per the weather agency, rainfall between 96% and 104% of the long-period average, which is 87 cm, is considered “normal”. Rainfall less than 90% of this measure is considered “deficient”, between 90% and 95% “below normal”, between 105% and 110% “above normal” and more than 110% is considered “excess” precipitation.

On Tuesday, Mrutyunjay Mohapatra, the agency’s director-general, told The Indian Express that the higher-than-normal minimum temperatures seen over North India, along with the presence and strengthening of westerly winds in the lower atmospheric levels, indicated an early monsoon onset.

Factors also included the presence and strengthening of easterly winds over the upper atmospheric levels, early pre-monsoon rainfall accompanied by thunderstorms realised over the southern peninsular for about 40 days and prevailing higher-than-normal pressure over the northwest Pacific Ocean, he said.

“All these factors support the early monsoon onset over Kerala,” the newspaper quoted Mohapatra as saying. “The prevailing wind conditions indicate strengthening of monsoon winds.”

Both the Indian weather model and several other global weather models were in consensus and suggested heightened rainfall activity over Kerala before June 1, he added.