Deep beneath the Pacific Ocean, a massive body of warm water has been moving steadily eastward for months. Originating near Indonesia, the underwater surge has travelled along the equator across nearly 14,500 kilometres of the tropical Pacific, according to scientists.
Although invisible from the surface, the phenomenon was detected by a NASA satellite orbiting about 1,300 kilometres above Earth. As the warm water advanced, it caused the ocean surface above it to rise by roughly 15 centimetres.
That subtle rise, observed during the spring of 2026, served as an early indication of changing ocean conditions. On June 11, the US National Oceanic and Atmospheric Administration (NOAA) officially declared the onset of El Niño, with forecasters warning that it could strengthen into a rare and powerful event.
El Niño represents the warm phase of a naturally occurring climate cycle in which the central and eastern Pacific Ocean experience above-average temperatures, altering weather patterns across the globe. The term was coined by fishermen centuries ago and is Spanish for "the boy," referring to the Christ Child because the warming typically peaked around Christmas.
How a Kelvin wave triggers El Niño
Under normal conditions, trade winds blow from east to west across the Pacific, pushing warm surface water toward Indonesia while allowing cold, nutrient-rich water to rise near the coast of Peru through a process known as upwelling.
At times, however, these trade winds weaken or briefly reverse. When this happens, the accumulated warm water in the western Pacific begins moving eastward as a massive underwater pulse known as a Kelvin wave.
Because warm water occupies more space than cold water, it raises the ocean surface above it. The wave also forces the thermocline—the boundary separating warm surface water from colder deep water—to sink, reducing the upwelling of cold water near South America.
As a result, sea surface temperatures in the eastern Pacific increase, leading to the development of El Niño.
How NASA's Sentinel-6 detected it
The Sentinel-6 Michael Freilich satellite, launched in 2020 through a collaboration between NASA and its European partners, measures sea surface height across the globe every 10 days with extremely high precision.
The satellite first detected a relatively small Kelvin wave near Micronesia in late January, which weakened by mid-February. A much larger wave then formed in early March and continued moving eastward. By mid-May, sea levels off the coast of Peru were more than 15 centimetres above their long-term average.
Could 2026 see a super El Niño?
It remains a possibility. According to NOAA, there is a 63 per cent chance that Pacific Ocean temperatures will rise more than 2 degrees Celsius above average, a threshold associated with very strong El Niño events such as those recorded in 1997 and 2015.
For India, such a development could pose challenges, as strong El Niño events have historically been linked to weaker southwest monsoons. However, other climate factors, including the Indian Ocean Dipole, can influence and sometimes reduce its impact.
Forecasters expect the event to reach its peak during the coming winter, with global weather patterns likely to be affected in the months ahead.
