Introduction
The global climate system is a complex interplay of various factors, with the El Niño-Southern Oscillation (ENSO) standing out as a significant driver of worldwide weather patterns. Recent observations and expert analyses point towards a notable shift in this system. This article delves into the current state of ENSO, focusing on the transition to ENSO-neutral conditions, a state often described as a “Nada Diagnosis” in terms of extreme climate patterns. We will explore the oceanic and atmospheric indicators that underpin this diagnosis, providing a comprehensive understanding of what ENSO-neutral signifies and its potential implications.
Current Oceanic Conditions: Weakening La Niña
February 2025 marked a significant turning point in the equatorial Pacific Ocean. Sea surface temperatures (SSTs), a crucial indicator of ENSO, displayed a clear weakening of below-average conditions across the central and east-central regions []. This retreat of cooler waters is visually represented in Figure 1, signaling a departure from the La Niña phase. The Niño indices, which quantify SST anomalies in specific areas of the Pacific, corroborated this trend. Weekly readings showed a diminishing presence of below-average temperatures, particularly in the Niño-3.4 and Niño-4 regions []. Figure 2 illustrates this decline through the Niño index values, further solidifying the oceanic transition.
However, the SST landscape was not uniformly cool. Coastal waters near South America experienced notable warming, with the latest Niño-1+2 value reaching 1.6°C. It’s important to note that this warming was confined to the upper 50 meters of the ocean and linked to low-level westerly wind anomalies in the eastern Pacific. Subsurface temperatures also reflected the weakening La Niña, with negative anomalies diminishing []. Figure 3 shows the reduction in these subsurface anomalies. Despite this weakening, deeper negative anomalies persisted in the eastern Pacific and extended to a depth of 200 meters in the central Pacific []. Figure 4 highlights these persistent deep anomalies, indicating that the transition is still underway and complex.
Atmospheric Indicators: Echoes of La Niña Fading
The atmospheric component of ENSO, equally critical to diagnosis, also mirrored the oceanic trends. Tropical Pacific atmospheric anomalies continued to exhibit characteristics of La Niña, albeit in a weakening state. Low-level winds maintained an easterly direction over the western and central Pacific, while upper-level winds displayed westerly anomalies over the east-central Pacific. Convection patterns, indicative of atmospheric circulation, showed suppression around the Date Line and enhancement near Indonesia []. Figure 5 visualizes these atmospheric anomaly patterns. Furthermore, both the traditional and equatorial Southern Oscillation Indices (SOIs), which measure pressure differences linked to ENSO, remained positive. Collectively, these atmospheric indicators, while still showing remnants of La Niña, supported the overall picture of a coupled ocean-atmosphere system trending towards ENSO-neutral conditions.
Forecast and Outlook: The Nada Diagnosis of ENSO-Neutral
Predictive models from the IRI (International Research Institute for Climate and Society) and the North American multi-model ensemble strongly suggest a transition to ENSO-neutral in the approaching season []. Figure 6 presents these model forecasts, converging on the ENSO-neutral prediction. Expert consensus aligns with these models, forecasting ENSO-neutral conditions with a probability exceeding 50% through July-September 2025. This “nada diagnosis” – indicating the absence of both El Niño and La Niña – is favored to develop imminently and persist throughout the Northern Hemisphere summer, with a 62% chance for June-August 2025 []. Figure 7 illustrates the probabilistic forecast for ENSO-neutral.
It is crucial to acknowledge the inherent uncertainty in forecasts, particularly those extending further into the future, especially when made during the spring season. While ENSO-neutral is the most probable outcome in the near term, longer-range predictions carry greater uncertainty, with no single outcome exceeding a 50% chance. Notably, the probability of El Niño development remains the lowest among the possibilities.
Conclusion: Navigating Climate Variability in ENSO-Neutral
In summary, the current climate diagnosis points towards a decisive shift towards ENSO-neutral conditions. Oceanic and atmospheric indicators, while still showing vestiges of the preceding La Niña, are converging towards a state characterized by the absence of strong El Niño or La Niña influences. This “nada diagnosis” of ENSO-neutrality signifies a period of relative equilibrium in the ENSO cycle. While ENSO-neutral does not imply a lack of climate variability, it suggests a reduced influence from these major climate drivers, potentially allowing other regional and global climate patterns to exert more influence. Continued monitoring and analysis will be essential to fully understand the evolution of ENSO and its broader impacts on global weather and climate in the coming months.
This discussion is a collaborative effort from the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their affiliated institutions. For weekly updates on oceanic and atmospheric conditions, please visit the Climate Prediction Center website (El Niño/La Niña Current Conditions and Expert Discussions). Further analysis and perspectives can be found on the ENSO blog. A probabilistic strength forecast is available here. The next ENSO Diagnostics Discussion is scheduled for 10 April 2025. To subscribe to email notifications for monthly ENSO Diagnostic Discussions releases, please email [email protected].
