May 2025 ENSO update: eye of neutral

The tropical Pacific is in ENSO-neutral conditions, and neutral is expected to continue through the Northern Hemisphere summer. Neutral is also the most likely outcome for the fall and winter, although chances of La Niña are a close second. Today, as your trusty representative of the ENSO forecast team, I’ll cover current conditions in the tropical Pacific, what we mean by neutral, and what it means for seasonal climate prediction… with a side of Macbeth (footnote 1).

The ENSO cauldron

First, let’s set the stage for why we care so much about El Niño and La Niña, the natural climate pattern collectively known as ENSO, the El Niño/Southern Oscillation. El Niño and La Niña change global atmospheric circulation and the jet streams in known ways, with impacts on extreme rain, drought, snow, heatwaves, the range of daily temperature, tornado and hurricane seasons, global crop yields and disease outbreaks, and many others. El Niño and La Niña can be predicted many months in advance, so they provide an early picture of potential climate conditions and allow for preparation and planning.

If it were done when 'tis done

Our primary yardstick for ENSO is how the temperature of the ocean surface in the Niño-3.4 region of the central tropical Pacific compares to the long-term average. (Long-term is currently 1991–2020). Warmer than average by 0.5 °Celsius (0.9 °F) or more is El Niño, while cooler than average by 0.5 C or more is La Niña. Between them—within 0.5 °C of average—is ENSO-neutral territory.

April 2025 sea surface temperature compared to the 1985-1993 average (details on climatology from Coral Reef Watch). The box indicates the location of the Niño-3.4 ENSO-monitoring region in the tropical Pacific. The surface of the east-central tropical Pacific is near average, while much of the global ocean remains warmer than average. NOAA Climate.gov image from Data Snapshots.

According to our most reliable long-term sea surface temperature dataset (see footnote), the Niño-3.4 region was just 0.16 °C (0.3 °F) cooler than the long-term average in April. This is solidly in ENSO-neutral territory for the second month in a row.

2-year history of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for all La Nina events since 1950 (gray lines) and the recent (2024-25) event (purple line). The Niño-3.4 index has been near average for the past two months. Graph by Emily Becker based on monthly Niño-3.4 index data from CPC using ERSSTv5.

We ENSO forecasters also monitor the temperature of the water under the surface of the tropical Pacific because it can reinforce or change temperatures at the surface. Currently, the subsurface is also very close to the long-term average.

Turning to the atmospheric side of ENSO, some features are reminiscent of La Niña, but the brew this month has more ENSO-neutral flavors. We monitor many different aspects of the Walker circulation, the overturning atmospheric circulation in the tropical Pacific, to get a full picture of the strength of the circulation. During El Niño, the Walker circulation is weakened: weaker easterly (from the east) trade winds, a rainier central Pacific, and drier Indonesia. La Niña strengthens the circulation: stronger trade winds, a drier central Pacific, and a wetter Indonesia. When ENSO is neutral, winds, rainfall, and cloudiness are all near average.

Two ways of looking at the atmospheric conditions in the tropical Pacific: the Equatorial Southern Oscillation (left) and cloudiness in the central Pacific (right). The colored lines show 2024–25, while the gray lines are every La Niña on record since 1979. Both measurements provide evidence that the Walker circulation strength is near to average, after several months of being stronger than average. Climate.gov graph, based on data from Michelle L’Heureux.

Currently, we find that cloud cover over the central tropical Pacific is slightly reduced, easterly trade winds are modestly stronger than average near the Date Line, and the sea level pressure pattern across the Pacific (as measured by the Equatorial Southern Oscillation Index) is slightly positive. All these indicators are consistent with a stronger Walker circulation, so the tropical Pacific atmosphere is maintaining a slight La Niña-ish lean. However, these are the closest to average we’ve seen in some time, and these monthly measures of the tropical atmosphere bounce around a lot more than the ocean ones.  

Nothing is but what is not

A question we often get here at the ENSO Blog is “what are the impacts of neutral?” That’s a great question! After all, I listed a whole bunch of effects from El Niño and La Niña in the second paragraph of this very post. However, neutral doesn't have a signature pattern of weather effects. When El Niño or La Niña are in charge, they change atmospheric circulation and push the jet streams around in specific ways, leading to their typical impacts, and making the seasonal climate more predictable. In their absence—that is, neutral conditions—other, less predictable weather and climate patterns can be more important.

Concept by Tom Di Liberto and illustration by Emily Greenhalgh, NOAA Climate.gov.

Examples of other climate patterns include the North Atlantic Oscillation and the Madden-Julian Oscillation, both of which are known to influence temperature and rain/snow. However, they are largely only predictable a few weeks in advance, so they don’t give us the same kind of long-range prediction edge as El Niño or La Niña.

If you can look into the seeds of time and say which grain will grow and which will not

The current outlook for ENSO is very similar to last month’s, with a 74% chance of neutral through the summer. Neutral continues to be the most likely scenario through the winter, although La Niña is a close second. Odds of El Niño next winter are relatively small, at about 15%.

Out of the three climate possibilities—La Niña, El Niño, and neutral—forecasts say that ENSO-neutral conditions (gray bars) are most likely for the Northern Hemisphere spring and summer. Looking out to the fall, neutral is still the most likely, but chances for either La Niña (blue bars) or El Niño (red bars) are increasing. NOAA Climate Prediction Center image.  

ENSO prediction in the spring is notoriously difficult, a time known as the “spring predictability barrier.” (Check here and here for more details on the spring predictability barrier.) In the coming months, we’ll emerge from this period, and as we draw closer to the winter, our forecasts should gradually become more confident. 

A little peek behind the scenes: when Michelle was drafting this month’s ENSO Diagnostic Discussion, she messaged the team to say it was tough not just to repeat April’s discussion. This is another difficulty of ENSO-neutral conditions! It’s been a long time since we’ve had an extended stretch of neutral (you can check out our 75-year historical record of ENSO here). But that doesn’t mean we’re out of things to talk about here at the ENSO Blog, so watch this space!

Footnotes

1: All the section headings are quotes from Shakespeare’s Macbeth. Should I have used quotation marks? Maybe. But we all agreed that looked weird.

2: For official ENSO monitoring, we use the Extended Reconstructed Sea Surface Temperature data set, now on its 5^th version. Details on what’s in the latest update are available from NOAA National Centers for Environmental Information.