Thiruvananthapuram: The coastal areas of Kerala and southern Tamil Nadu are likely to experience the 'kallakkadal' phenomenon - the sudden swell of the seas causing rough waves - from 2.30 am on Saturday to 11.30 pm on Sunday, weather agencies said, issuing alerts to fishermen and coastal residents.

"There is a possibility of rough seas due to high waves of 0.5 to 1.5 metres during this period," according to the Indian National Centre for Ocean Information Services (INCOIS).

INCOIS, the central agency that issues weather warnings for fishermen in the country, advised people to safely moor their fishing vessels in the harbour.

In a statement, the Kerala State Disaster Management Authority (KSDMA) and other weather agencies advised people to stay away from danger zones as per the instructions of the authorities, as the rough sea conditions are likely to intensify.

"Keeping a safe distance between boats can avoid the risk of collision. The safety of fishing equipment should be ensured," they said in a statement here.

The agencies also advised people to avoid trips to the beach and completely stay away from activities at sea.

The term 'kallakkadal' literally means a sea that comes suddenly like a thief.

INCOIS has said that the swells result from strong winds in the southern part of the Indian Ocean at certain times, and that they occur suddenly without any particular indications or warning. Hence the name 'kallakkadal'. PTI