THIRUVANANTHAPURAM: The entire coastal areas of Kerala and the southern coastal parts of Tamil Nadu are likely to experience the "kallakkadal phenomenon" -- the sudden swell of the seas causing rough waves -- until 11.30 pm on Monday, prompting a central agency to issue alerts to fishermen and coastal residents.

"As the rough seas are likely to intensify, stay away from the danger zone areas as per the instructions of the authorities," according to the Indian National Centre for Ocean Information Services (INCOIS).

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

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

INCOIS also advised people to avoid trips to the beach and activities at sea completely.

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

INCOIS has said that the swell surge is the result of strong winds in the southern part of the Indian Ocean at certain times occurring suddenly without any particular indications or warning, hence the name "kallakkadal."