The number that caught forecasters’ attention arrived in NOAA’s weekly Niño 3.4 update for the week ending May 18, 2026: the sea surface temperature anomaly in the benchmark region had reached +1.9°C, a value that exceeds where both the 1997-98 and 2015-16 super El Niño events stood at the same point in their respective development cycles. Those two episodes each inflicted an estimated $35 billion or more in global economic damage through droughts, floods, coral bleaching, and disrupted food production. The tropical Pacific is now on a steeper warming curve than either of them followed.
“We are watching the Niño 3.4 index very carefully because the rate of warming this spring has been exceptional,” said Michelle L’Heureux, a physical scientist and ENSO forecaster at NOAA’s Climate Prediction Center. “At this stage in 1997 and 2015, the anomaly was still below where we are now, and that has significant implications for how strong this event could become by winter.”
That does not mean the outcome is locked in. But for emergency planners in drought-vulnerable parts of Africa and South America, agricultural forecasters watching grain belts from Australia to the U.S. Midwest, and coastal communities preparing for shifted storm tracks, the early signal is impossible to ignore.
What the data show
The comparison rests on NOAA’s own index records. The Climate Prediction Center publishes weekly and monthly ENSO indices for the Niño 3.4 region, the strip of equatorial Pacific between 170°W and 120°W whose temperature anomalies underpin most El Niño strength classifications. A separate downloadable anomaly record, calculated from ERSSTv5 values, provides the reproducible time series needed to align ramp-up months across all three events. When those records are placed side by side through the spring development phase, the May 2026 Niño 3.4 anomaly of +1.9°C sits above where both 1997 and 2015 stood at comparable points: the 1997 event registered roughly +1.5°C and the 2015 event roughly +1.6°C during the equivalent week of their development.
NOAA has used this kind of month-by-month overlay before. Its June 2023 ENSO discussion plotted the evolution of the 2023-24 El Niño against the 1997 and 2015 trajectories as a reference frame. That earlier event, which peaked in late 2023 and faded through the first half of 2024, is a separate cycle from the one now developing. The 2023 discussion is relevant here only because it established the analytical method: overlaying Niño 3.4 curves from different events to compare their pace of development. The same approach, applied to the current 2026 cycle using CPC’s Relative Oceanic Niño Index (RONI) framework, shows the new event pulling ahead during the months when many past El Niños have stalled or plateaued.
The evidence runs deeper than the ocean surface. Subsurface cross-sections published in NOAA’s ENSO updates reveal how warm water builds beneath the thermocline during the early months of an event. That subsurface heat content acts as a reservoir: the larger and deeper the pool of anomalously warm water, the more energy is available to sustain and amplify the surface signal in the months ahead. In the current cycle, a thick wedge of above-normal temperatures extends well below the surface across much of the central and eastern equatorial Pacific, an arrangement that historically has preceded strong peaks.
“The subsurface heat loading we are seeing right now is remarkable,” said Andrew Wittenberg, a research oceanographer at NOAA’s Geophysical Fluid Dynamics Laboratory. “It is one of the clearest indicators that this event has the energy budget to sustain itself well into the northern winter.”
Cross-agency observations reinforce the picture. NASA’s Earth Observatory has documented how the 1997-98 and 2015-16 events differed in spatial extent and sea-level response, linking SST anomalies with rainfall shifts and ocean height changes measured by satellite altimetry from the Jet Propulsion Laboratory. Those benchmarks give scientists a way to judge whether the current event’s sea-level signature is tracking ahead of, or behind, the two earlier giants. So far, the pattern is consistent with a strong and expanding event.
On the atmospheric side, the classic fingerprints of El Niño are already visible: weakened trade winds over the central Pacific, a shift in deep convection eastward from the Maritime Continent, and early adjustments to the subtropical jet streams that steer mid-latitude weather. These responses are still developing, but they are consistent with the oceanic signal and confirm that the Pacific has moved firmly into El Niño territory rather than hovering near a borderline state.
Why a fast start does not guarantee a record finish
Speed and magnitude are not the same thing. The 2015-16 event built rapidly in its early months but ultimately peaked at roughly the same Niño 3.4 magnitude as 1997-98, despite a different spatial footprint and a distinct set of regional impacts. Research published in Geoscience Letters has examined why: off-equatorial wind patterns drove a strong autumn acceleration during the 2023-24 El Niño cycle, a mechanism that differed from the more equatorially confined dynamics of 2015. Whether similar wind patterns will persist long enough to push the current event past historical peaks is a question the observational record cannot yet answer.
CPC’s May 2026 ENSO strength probabilities, released on May 15, 2026, and built on the RONI framework, break the forecast into three-month seasonal windows and assign likelihoods to each strength category. The threshold for “strong” sits at a Niño 3.4 anomaly of +2.0°C or above. The current probability distribution still leaves room for a peak that falls short of the most extreme historical values, even as the early-season numbers resemble the ramp-up to 1997 and 2015.
NOAA’s Geophysical Fluid Dynamics Laboratory adds another layer of guidance through its SPEAR coupled ocean-atmosphere model. The May 2026 ensemble, initialized with the latest ocean observations, shows a wide spread: some members project a powerful event while others level off at moderate strength. That spread reflects real uncertainties in processes like the persistence of westerly wind bursts along the equator, the timing of upwelling pulses, and how tropical variability interacts with slower-moving background trends in the Pacific basin.
What this means for the months ahead
The global weather consequences of El Niño depend not just on how warm the central Pacific gets, but on how tightly the atmosphere couples to that warmth. No primary institutional dataset currently offers a clean, side-by-side comparison of Walker circulation shifts at this stage of the current event against the same phase in 1997 or 2015. That gap matters because the teleconnections that deliver El Niño’s impacts to distant continents can amplify or muffle the oceanic signal in ways that are difficult to predict months in advance. A strong oceanic event can produce muted impacts if the atmospheric response is loosely coupled; a more moderate Niño can still trigger outsized regional extremes if the teleconnections align in a particularly sensitive configuration.
Timing is another wild card. Many of El Niño’s most consequential effects hinge on when peak anomalies arrive relative to specific seasons: boreal winter for North American precipitation shifts, the Southern Hemisphere growing season for drought stress in parts of sub-Saharan Africa and Brazil, and late summer through autumn for suppression of Atlantic hurricane activity. A peak that lands a month or two earlier or later than expected can reshape which regions bear the heaviest burden. Forecast systems have improved, but they still carry enough uncertainty that planners must prepare for a range of plausible calendars.
There is also the question of background warming. Every El Niño now develops on top of a Pacific Ocean that is warmer than the long-term average, a baseline shift driven by decades of accumulated greenhouse heating. That means even a Niño 3.4 anomaly that matches 1997 or 2015 in relative terms translates to higher absolute sea surface temperatures, with potential knock-on effects for marine ecosystems, coral bleaching thresholds, and the total moisture available to fuel extreme rainfall events.
How forecasting centers will track the event through northern summer
The verified data tell a clear but incomplete story. Sea surface temperatures in the Niño 3.4 region, backed by subsurface heat content and consistent atmospheric signals, show an El Niño that has warmed more quickly through its development phase than either of its two most notorious predecessors. Model ensembles, probabilistic outlooks, and gaps in teleconnection monitoring all caution against treating a rapid start as a guarantee of a record-breaking finish.
For the communities most exposed to El Niño’s reach, the practical takeaway is straightforward: the window for preparation is now, not after the peak arrives. Forecasting centers including NOAA’s Climate Prediction Center, the Australian Bureau of Meteorology, and the WMO’s regional climate outlook forums will update their guidance as fresh ocean and atmosphere data come in through June 2026 and beyond. The difference between a merely strong El Niño and a truly historic one will be determined not only by how high the Pacific’s temperature climbs, but by how the atmosphere responds to that heat in the weeks and months that follow.
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*This article was researched with the help of AI, with human editors creating the final content.
