Federal weather officials confirmed today that El Niño has officially developed in the tropical Pacific Ocean, with forecasters issuing an El Niño Advisory as the climate phenomenon is anticipated to grow stronger through the fall season.
The National Weather Service announced that El Niño, which represents the warm phase of the El Niño Southern Oscillation climate pattern, is projected to reach moderate or strong intensity this autumn. Weather experts predict a 63% probability that sea surface temperatures will rise more than 2.0°C above normal in the Pacific monitoring zone. Should temperatures cross this threshold, NOAA would classify the event as a “very strong” El Niño.
El Niño occurs when equatorial Pacific Ocean temperatures climb 0.5°C above typical levels for multiple consecutive months. Weather scientists also track atmospheric conditions over this Pacific region, monitoring for changes in the Walker Circulation – a large-scale east-to-west airflow pattern created by temperature and pressure variations between the warm western Pacific and cooler eastern waters. El Niño is declared when this circulation pattern weakens and warmer waters move eastward toward South America.
The climate pattern typically reaches peak strength during winter months, with its most significant global effects occurring during northern hemisphere winter seasons. During typical El Niño winters, the jet stream over the northern Pacific tends to move southward, directing storm systems across the southern portion of the United States. This southward shift also creates drier conditions over the Northern Rockies and Ohio and Tennessee river valleys. Temperature-wise, El Niño frequently produces warmer than normal winter conditions across northern U.S. regions.
“Every El Niño is not the same; each one is unique with its own imprint on our weather,” stated Ken Graham, director of NOAA’s National Weather Service. “Advanced monitoring and an improved understanding of El Niño patterns allow the NWS to better predict and better prepare the public and our core partners for what is to come.”
Common El Niño impacts include stronger upper-level winds that typically reduce storm and hurricane formation in the Atlantic Basin, while weaker winds encourage tropical development in the eastern and central Pacific regions. The phenomenon also brings stormier conditions to the Southern U.S., increasing chances for both rain and snow during El Niño winters.
High tide flooding risks may increase in parts of the United States, particularly along the West Coast. The climate pattern also affects marine life migration patterns, with warm water species moving northward while cold water species relocate farther north or into deeper waters. These behavioral shifts impact fish growth, survival, and reproduction rates. Previous El Niño episodes have also contributed to increased harmful algal bloom formation along the U.S. West Coast.
In February, NOAA officially began using the Relative Oceanic Niño Index for monitoring sea surface temperatures and predicting El Niño and La Niña events. Unlike the traditional Oceanic Niño Index, which uses a fixed 30-year temperature baseline, the new index updates monthly, providing more reliable identification of climate events.
NOAA’s climate monitoring team has tracked both the traditional and new indices since 2021. After observing several years of climate phases and corresponding atmospheric responses, scientists determined that the new index better correlates with expected Walker Circulation changes, offering more valuable information to weather experts, emergency managers, and the public.
