What El Niño Is and Why the 2026 Event Is Reshaping Weather Worldwide

El Niño is not a storm or a single weather event. It is a temporary shift in ocean temperature and wind patterns across the tropical Pacific that reorganizes rainfall, temperature and storm tracks across much of the planet. The current event, declared in mid-2026, has grown into what multiple forecasting agencies call an exceptionally strong episode, prompting renewed public interest in how the phenomenon actually works and why it matters for people far from the Pacific.

How El Niño forms

Under normal conditions, easterly trade winds push warm surface water across the equatorial Pacific toward Asia, keeping the eastern Pacific, off South America, relatively cool, according to NASA's Earth science program. El Niño begins when those trade winds weaken or even reverse direction. Warm water that would normally pile up near Indonesia instead spreads eastward toward the Americas, and the atmospheric circulation pattern known as the Walker circulation shifts with it.

NASA states that scientists officially classify an El Niño once sea surface temperatures in a reference region of the central Pacific called Niño 3.4 stay more than 0.5°C above the long-term average for five consecutive months. The U.S. National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory (NOAA PMEL) describes El Niño more broadly as a large-scale weakening of trade winds combined with warming of the eastern and central equatorial Pacific surface layer, noting such events recur roughly every three to four years and typically persist 12 to 18 months; NASA puts the natural recurrence interval at every two to seven years, with impacts usually peaking between November and January.

The 2026 event: an exceptionally strong El Niño

NOAA declared El Niño conditions on June 11, 2026, and forecast at the time a 63% chance that sea surface temperatures would exceed 2.0°C above average — the threshold for a 'very strong' event — by winter. By early September, the World Meteorological Organization (WMO) reported the event was firmly established and intensifying, with the Niño 3.4 index running 2.2°C to 2.6°C above average in late July and mid-August, and subsurface Pacific waters locally more than 8°C above normal. WMO put the likelihood of El Niño persisting through February 2027 at close to 100%, with the peak expected toward the end of 2026.

Because the readings are so far outside the historical record, researchers have had to adjust how they measure the event. Inside Climate News reported that scientists introduced a new metric, the Relative Oceanic Niño Index (RONI), after the standard Oceanic Niño Index produced record-breaking numbers that were difficult to compare with past events; by the new measure, the 2026 event ties the 1997-98 El Niño as the strongest on record for late August. Daniel Swain, a climate scientist with the California Institute for Water Resources at UC Agriculture and Natural Resources, told the outlet the current reading is 'so far above anything we've previously seen, it doesn't even fit on the same axis.' Inside Climate News also cited a study published in the journal Science suggesting the event is likely the strongest in more than a millennium, and reported Swain's assessment that related global temperature spikes could approach 1.7°C above his reference baseline, potentially breaking recent global heat records by a wide margin.

How El Niño changes weather around the world

NASA describes a consistent global pattern linked to El Niño, though the intensity varies by event. Indonesia, mainland Southeast Asia and northern Australia typically see below-normal rainfall and drought risk as the rain-bearing warm pool shifts east. South American desert regions, including parts of Peru and Ecuador, can experience unusual flooding, while the western United States and Mexico tend toward wetter conditions. Reduced upwelling of cold, nutrient-rich water off Peru can disrupt fish populations that anchor local fisheries. In the Atlantic and Pacific storm basins, El Niño is historically associated with fewer Atlantic hurricanes but more active eastern and central Pacific tropical cyclone seasons.

NOAA's U.S. winter outlook, issued alongside its June 2026 El Niño advisory, projects the jet stream shifting southward, steering the storm track toward the southern United States. That typically brings warmer-than-usual temperatures to the northern U.S. and increased rain and snow across the South, while the northern Rockies and the Ohio and Tennessee valleys tend to be drier. NOAA also flagged an elevated risk of high-tide coastal flooding, particularly on the West Coast. National Weather Service Director Ken Graham noted that every El Niño behaves somewhat differently, saying improved monitoring tools now help communities prepare for whichever imprint a given event leaves.

Sources: NASA Earth science program; NOAA Pacific Marine Environmental Laboratory (PMEL) definitions page.

Regional stakes: the California example

Inside Climate News, drawing on Swain's analysis, reported that the current event raises specific risks for California: a temporary rise in sea level of roughly one foot is possible by December, adding to an estimated 8 to 12 inches of sea-level rise attributed to climate change over the past century, which Swain said would compound coastal and bay-area flooding risks, particularly in November and December. The outlet reported that a wetter-than-average winter is considered extremely likely for California, especially the southern part of the state, and noted that past strong events in 1982-83 and 1997-98 caused significant coastal erosion, including landslides that damaged highways, and flooding in areas such as Marin County, Napa County and Palo Alto.

What happens next

Both NOAA and WMO expect the event to peak before winter ends and to persist into early 2027. NOAA's June 2026 forecast pointed to a peak during the 2026-27 winter, while WMO's September update placed the peak toward the end of 2026 with near-certain persistence through February 2027. WMO Secretary-General Celeste Saulo has said the scale of this El Niño calls for an equally significant level of preparation and coordinated response from national weather services and governments. Both agencies caution that the overall strength of an El Niño event, as measured by ocean temperature, does not by itself determine how severe the impact will be in any single region — local rainfall, drought and storm outcomes still depend on additional factors specific to each place and season.