Calm seas, distant storms: Why swell surges are hitting Kerala repeatedly

A swell surge is a sudden arrival of unusually large waves created by ocean swells. Fishermen commonly call it kallakadal. The waves are produced far from the coast, often by distant storms or prolonged, fierce winds. This makes swell surge different from ordinary monsoon waves, which are linked more directly to local seasonal winds and sea conditions.

For example, powerful winds in the southern Indian Ocean can generate swells. Those waves then travel north for two or three days before striking Kerala or southern Tamil Nadu. During this year’s calmer monsoon sea, these distant waves became easier to notice because the usual local monsoon waves were largely missing.

The distinction matters because a calm-looking sea can still become dangerous quickly. Swell surges can cause strong waves, coastal flooding, erosion and damage to fishing vessels. INCOIS has therefore issued repeated alerts, including red alerts, even while normal monsoon conditions appeared unusually quiet.

Swell waves are remarkable for both their size and reach. They can carry energy across thousands of kilometres after forming far from the coast. INCOIS said the powerful waves affecting India often originate about 1,000–2,000 kilometres away. Their distance from the source does not make them harmless; they can still arrive with enough force to flood coastal areas and threaten boats.

The usual route begins in the southern Indian Ocean. Strong winds create the swell there, and the waves travel northward for two or three days. On reaching shallow coastal waters, their energy produces heavy, forceful waves at the shore. Alappuzha, for example, saw coastal roads flood and traffic disrupted on Sunday.

The frequency this year has been unusual. Since the southwest monsoon began, Kerala has received 14 swell-surge alerts. Two were red alerts. INCOIS also warned coastal Karnataka, while Kerala and southern Tamil Nadu faced continuing high-risk conditions.

Swell surges reach southern Kerala and coastal Tamil Nadu strongly because of their position. Powerful waves generated in the southern Indian Ocean travel northward. Southern Kerala and the Kanyakumari region are among the first parts of India in their path. This gives the waves less opportunity to lose their strength before arrival.

The nearby sea is also deep. According to INCOIS, this deep water allows swell waves to retain much of their energy. When the waves approach the shoreline, they can therefore strike with considerable force. The waves may arrive even when local weather looks calm and ordinary monsoon conditions are weak.

This geography explains why alerts often focus on Kerala, southern Tamil Nadu and nearby western-coast areas. INCOIS issued a red alert along Kerala’s entire coast and southern Tamil Nadu, while coastal Karnataka received an orange alert. The warnings cover strong waves, erosion, flooding and risks to fishing vessels.

Swell-surge alerts were usually associated mainly with the pre-monsoon period. This year was different because El Niño influenced sea conditions during the southwest monsoon. The usual monsoon waves and winds were largely missing, leaving the local sea calmer than normal. That allowed distant swell waves to become a separate and repeated hazard.

In previous years, local monsoon waves and incoming swell waves commonly combined to create rough seas. It was difficult to identify how much of the danger came from swell surges alone. Separate swell-surge alerts were therefore less necessary. This year, the contrast was clearer: a calm local sea could suddenly receive powerful waves from far away.

Since the monsoon began, Kerala has recorded 14 alerts, including two red alerts. Calm conditions also encouraged fishing and other coastal activity, increasing exposure. INCOIS says it remains uncertain whether these events will continue after the monsoon withdraws, especially under prevailing El Niño conditions.

El Niño influenced this year’s regional sea conditions by weakening the usual monsoon waves and winds. As a result, the sea near Kerala appeared relatively calm. That calmness describes local conditions; it does not stop large swells already generated by powerful weather systems far away.

Strong winds in the southern Indian Ocean transferred energy into the water and created swell waves. Those waves travelled north for two or three days, sometimes from 1,000–2,000 kilometres away. With fewer local monsoon waves present, the incoming swells were easier to distinguish. In earlier years, both types of waves mixed together in generally rough seas.

This creates a deceptive risk. Fishing and other activities may increase because the local sea looks safer, yet distant swells can still arrive suddenly. That is why INCOIS issued repeated warnings this monsoon. Officials are also watching whether swell-surge events continue into the post-monsoon period.

When a swell surge reaches shore, its powerful waves can create several hazards at once. The article warns of strong waves, sea erosion, coastal flooding and fishing vessels being washed away. Roads may become flooded, beaches dangerous and coastal homes more exposed to erosion or incoming water. People near the shoreline can be injured or trapped.

Alappuzha provided a clear example. Heavy waves flooded coastal roads and disrupted traffic. In response to a red alert, Kerala’s disaster authority warned fishermen not to launch small vessels or beach them during the alert period. It also advised avoiding entertainment and leisure activities along beaches and the sea.

The danger can be especially deceptive during this year’s calm monsoon. Fishing and recreation may continue because ordinary rough-sea conditions are missing. Yet distant swell waves can arrive with little visual warning. Authorities therefore urge vigilance even when the nearby sea does not look unusually rough.

A swell begins when powerful winds blow across the ocean for a long period. The moving air transfers large amounts of energy into the water. That energy builds high waves around the storm or gale area. The waves then move away from their source as an ocean swell, even after the original weather system is far away.

The article describes distant storms, including hurricanes, or long periods of fierce gale winds as possible causes. In the southern Indian Ocean, such winds can generate powerful swells. These waves travel north for two or three days and may cover 1,000–2,000 kilometres before reaching the Indian coast. Their energy can remain significant over that journey.

Near the shore, the approaching swell becomes a major coastal hazard. It can produce strong waves, flooding and erosion, and can threaten fishing vessels. Because the source is distant, local skies and nearby seas may look calm when the dangerous energy is already travelling toward land.