Newly Formed El Niño Likely to Be Among Strongest Ever, US Says

NOAA's National Weather Service announced the development of El Niño and issued an advisory, predicting it will intensify to a moderate or strong level this fall. There is a 63% chance that sea surface temperatures will exceed the 2.0°C threshold in the monitored Pacific region, which NOAA classifies as a "very strong" El Niño event. El Niño is declared when equatorial Pacific temperatures are 0.5°C above average for consecutive months, coupled with a breakdown in the Walker Circulation pattern.

Typical El Niño winters in the Northern Hemisphere often see the jet stream shift southward, leading to stormier weather across the southern U.S. and drier conditions in the Northern Rockies and Ohio and Tennessee valleys. Warmer winters are also common across the northern U.S. The phenomenon can suppress Atlantic hurricane development while enhancing tropical activity in the eastern and central Pacific basins. Impacts can also include higher risks of high tide flooding on the West Coast and changes in oceanic species migration, potentially enhancing harmful algal blooms.

NOAA has adopted the Relative Oceanic Nino Index (RONI) for monitoring sea surface temperatures, which evolves monthly and is considered more reliable than the traditional Oceanic Nino Index (ONI) for identifying El Niño and La Niña events. Scientists have been closely monitoring both indices and concluded that RONI correlates better with expected changes in the Walker Circulation.