El Niño likely to become a very strong event as California prepares for wet winter

The National Oceanic and Atmospheric Administration’s Climate Prediction Center reported Thursday that the El Niño developing in the Pacific Ocean has a 95% probability of becoming a “very strong” event, the strongest such pattern since 1950. The agency also estimates a roughly 70% chance that the anomaly will be the most intense on record for the modern era.

Research meteorologist Alexander Gershunov of the Scripps Institution of Oceanography said the forecast is converging on a strong, possibly unprecedented, El Niño and noted that the warming of the tropical Pacific adds significant heat to the global climate system. He added that the pattern could bring above-average rainfall to Southern California, primarily from cold-frontal storms that move farther south than usual.

Michelle L’Heureux, the El Niño team lead for the Climate Prediction Center, said the current conditions give a 69% chance the event will exceed 4.5 °C above baseline, a threshold never reached in the historical record dating back to 1950. She explained that a “very strong” El Niño requires equatorial Pacific temperatures at least 3.6 °C above baseline.

The potential impacts for California include higher-than-normal winter precipitation, increased risk of tropical-moisture-driven heavy rains, and a modest chance of stronger eastern-Pacific hurricane activity. NOAA research oceanographer Michael Jacox cautioned that, while no definitive effects on the West Coast have been observed yet, coastal trapped waves could begin to produce impacts as the season progresses.

July ocean temperatures in the El Niño-monitoring region were 2.41 °C above baseline, the second-highest July reading on record, trailing only the 1997 event. Forecasts for October through December indicate a 95% likelihood of a “very strong” El Niño, with the prime period for rainfall and snowfall impacts expected from December through March.