Kelvin Gravity Waves: The Hidden Machinery Driving El Niño (Which Hints at How Long It Could Last, and Gives Us an Indication of When It Might End)

The current El Nino seems destined to enter the record books. Having earned the titles Super and Godzilla El Niño, the current El Niño phase of the El Niño Southern Oscillation (ENSO) has already left (and continues to leave) fire scars across huge swaths of Indonesia. Its toll on human health, most notably in Indonesia, but also in Singapore and Malaysia, will be only be counted in the coming decades when the millions who inhaled the noxious fumes are faced with chronic respiratory illnesses.

For those of us who work in Climate Change, the ENSO is an ever-present and recurring seasonal hazard. Every Spring, we scan the sea-surface temperatures (SSTs) of the Eastern Pacific, looking for the telltale signs of warm surface water, the formation of low atmospheric pressure cells, and the changes in prevailing wind direction, that together, signal the arrival of the ‘little boy’.

And there are compelling reasons why we do (all the while, hoping that our ASEAN partners are doing likewise), as we now see, in hindsight, that planning, preparation and strong governance, including education and public awareness, go a long way toward reducing the inevitable environmental impacts and the cost to our regional national economies, both now, and in the future. Water table management in peatlands, a moratorium on fire-related land activities, the procurement and preparation of firefighting equipment and the mobilization and training of personnel, are but some of the many ‘no-regrets’ initiatives that should be implemented in preparation for an El Niño of this magnitude.

But exactly how do scientists know, even before the warm water appears off the coast of Ecuador that an El Niño is imminent? Likewise, and some would say, more importantly, how do they know when it might end? Like many things, we need to look at what’s happening beneath the surface.

Kelvin Waves deliver warm ocean water (in red) from the Western to the Eastern Pacific

The surface of the Pacific is a turbulent, chaotic interface where water clashes with the atmosphere,

exchanging heat in response to thermal gradients between the two. But slightly deeper, below the turbulent surface layer, and down to a depth of about 300m (left), a phenomenon known as Kelvin waves, large, slow-moving pulses of warm water shifting in response to pressure gradients, transfer warm water in a selfgenerated submarine conduit from the Western (Indonesian - left) end of the Pacific to the Eastern (Eucadorian - right) end, a journey of several months.

Data from NOAA’s Physical Sciences Laboratory (PSL), shown on the left tracks the passage of the warm water pulses, across the Pacific, from October of 2025 to September of 2026.

Upon arriving at the South American coastline, the heat contained in the pulse of warm water, around 100m thick, but more than 11,000 kilometers (approximately 100 degrees of longitude at the equator) in length, begins fueling the El Niño, evaporating water and transferring the heat to the atmosphere with every thunderstorm. Tropical thunderstorms move a significant amount of this heat, but the undisputed champion among natural heat engines is the tropical cyclone (also known variously as Typhoons in the Pacific or Hurricanes in the Atlantic). Over the course of many tropical cyclones, and their less organized relatives, tropical storms and tropical depressions, the reservoir of heat in the eastern Pacific is gradually dissipated to the atmosphere, returning the ENSO to its neutral phase.

But when can we expect this to occur? For businesses awaiting the return of the rains to Kalimantan, this determination could be economically critical. Once again, the scientific community provides some insight, this time, from the NOAA Climate Prediction Centre (CPC). A measure known as the Upper Ocean Heat Content (below) tracks the heat content anomaly of the warm water reservoir in the Eastern Pacific (between 180 degrees West and 100 degrees West, from the surface to a depth of 300m) and serves as a kind of ‘fuel gauge’ for the ongoing El Niño.

As seen in the graph below recounting two previous El Niño events from 1997 and 2015, shown in blue and green, respectively, with the current El Niño shown in red, the upper ocean heat content grows as the El Niño strengthens and, as heat is lost to the atmosphere, the anomaly returns to zero. In the El Niño events of 1997 and 2015, the El Niño peaked within one month after the Upper Ocean Heat Content curve began to to drop precipitously, indicating that the warm water reservoir had essentially been depleted of its heat.

The 2026 El Niño track, on the other hand, shows that as of September, the Upper Ocean Heat Content was, in fact, still increasing. This explains the CPC’s forecast of a strong-to-very strong El Niño likely through January–March 2027, a greater than 83% chance. On timing, its words are “El Niño will continue to strengthen through the end of the year” — it names no peak month. So even as businesses await the peak of the curve, they need to brace for a relentless El Niño through the end of the first quarter of 2027.