The Japan Meteorological Agency says the El Niño now underway in the Pacific has become the strongest it has measured, with sea surface temperatures in its monitoring region averaging 4.0 degrees Celsius (7.2 degrees Fahrenheit) above its baseline in September. That beats the previous high of 3.6°C set in December 1997, the largest value in records dating to 1949, according to JMA's El Niño monitoring bulletin issued Oct. 9.

JMA also expects the record-strength event to continue through the Northern Hemisphere winter, which it puts at a 100% probability. Its next monthly update is scheduled for Nov. 10.

The milestone matters because the 1997-98 El Niño is the benchmark many readers remember for damaging winter storms in California and the southern United States. A record in one agency's index does not guarantee a repeat of those impacts, but it raises the stakes for a winter that U.S. forecasters were already watching closely.

Three Agencies, Three Yardsticks

JMA's record is measured in its own monitoring region, the eastern equatorial Pacific between 5 degrees north and 5 degrees south and from 150 degrees west to 90 degrees west. That area extends farther east than the Niño 3.4 region that NOAA uses as its main measure, which partly explains why the numbers differ between agencies.

NOAA's Climate Prediction Center, in its Oct. 8 ENSO diagnostic discussion, kept an El Niño Advisory in place and reported a monthly Niño 3.4 anomaly of +2.1°C. It forecast "a strong-to-very strong El Niño likely through January-March 2027" and gave an 83% chance that the October-December period reaches its historic threshold, a three-month Relative Oceanic Niño Index of +2.5°C or more. NOAA said the event could exceed the strength of previous El Niño events dating back to 1950, but it has not declared a record.

The World Meteorological Organization, drawing on 13 forecasting centers, said the Niño 3.4 anomaly rose from +1.6°C in June to +2.5°C in August. It forecast an October-December anomaly of about +3.7°C, which would be the highest since observations began, above the previous record of +2.6°C from November 2015 to January 2016, according to its latest El Niño update.

"El Niño is firmly established and strengthening rapidly," WMO Secretary-General Celeste Saulo said. The agency gave a near-100% likelihood that El Niño persists through February 2027.

The comparisons are not interchangeable — and that matters for headlines. JMA's figure is a single month in its own region, WMO's is a seasonal forecast, and NOAA's historic threshold uses a relative index that adjusts for warming across the tropics. All three point the same direction, but readers should treat "strongest on record" as JMA's finding rather than a single global verdict.

Winter Signals for the Southern and Western U.S.

Strong El Niño events tend to shift the Pacific jet stream, which often brings wetter conditions to the southern United States and milder conditions to parts of the North. WMO's outlook lists parts of North America south of 45 degrees north latitude among regions favored for wetter-than-normal conditions this season.

Those are probabilities, not scheduled weather. NOAA's discussion says the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed, and it points readers to its seasonal outlooks for regional detail.

California has already acted on the risk. Nature World News previously reported that California declared a statewide emergency before winter as the El Niño built. Repeated storm swells have also eroded Southern California beaches this fall, leaving coastal neighborhoods more exposed to winter storms.

Higher-risk households include those in burn scars and on steep slopes, where heavy rain can trigger debris flows, and those in low-lying coastal and riverside areas. People in those places can review flood insurance now, since policies through the National Flood Insurance Program typically take 30 days to take effect, and clear gutters and drains before the rainy season.

Global Heat and Uneven Impacts Abroad

The record El Niño is unfolding in an already hot climate. WMO said August 2026 was the hottest August on record according to Copernicus, NOAA and NASA, and global sea surface temperatures reached an all-time observed high that month. Saulo noted that strong El Niño events often contribute to some of the hottest years on record, as happened in 2024.

The effects are uneven — some regions get too much rain, others too little. WMO's outlook favors wetter conditions in the Greater Horn of Africa and southeastern South America, and drier conditions across the Indian subcontinent, southern Central America, parts of the Caribbean and northwestern South America. Those shifts can affect crop yields and food prices far from the Pacific.

From Forecast to Record

Nature World News reported in September that El Niño was heading toward historic strength, when NOAA put a 75% chance on a historic event this fall. Since then, JMA has confirmed a record in its own index, NOAA has raised its October-December historic probability to 83% and WMO has forecast record Niño 3.4 values.

Several questions remain open, including whether NOAA's index crosses its historic threshold, how high the event peaks and how quickly it fades in 2027. NOAA's next monthly ENSO discussion is due in November, and JMA updates on Nov. 10.

The bottom line is that a major forecasting agency now says this El Niño is the strongest it has recorded, and others expect record values this winter. Households in flood- and debris-flow-prone parts of the southern and western U.S. should use the coming weeks to prepare, while relying on local National Weather Service forecasts as storms develop.

What Readers Want to Know

Is this El Niño really the strongest on record?

It is the strongest the Japan Meteorological Agency has recorded in its index, at +4.0°C in September versus +3.6°C in December 1997. NOAA has not yet declared a record in its own index.

Why do JMA, NOAA and WMO report different numbers?

They use different ocean regions and methods. JMA's monitoring region extends farther east than NOAA's Niño 3.4 region, and NOAA uses a relative index that adjusts for tropical warming.

How long will El Niño last?

JMA expects it to continue through winter, and WMO gives a near-100% chance that it persists through February 2027.

What could it mean for U.S. winter weather?

Strong El Niño winters often bring wetter conditions to the southern U.S. and milder weather to parts of the North, but impacts are not guaranteed.

Who should prepare now?

Residents near burn scars, steep slopes, rivers, and low-lying coasts in the southern and western U.S. should review flood insurance and clear drains before the rainy season.

When are the next official updates?

NOAA's next monthly ENSO discussion is due in November, and JMA plans its next bulletin on Nov. 10.