California is heading into winter with a very strong El Niño strengthening in the tropical Pacific and forecasters increasingly confident that the event could surpass previous records dating to 1950. The National Oceanic and Atmospheric Administration’s Climate Prediction Center said Thursday, Oct. 8, that temperatures in a key stretch of the tropical Pacific were 2.1 degrees Celsius above normal — just over the agency’s 2-degree threshold for a “very strong” El Niño. The center put the chance of the event setting a strength record between October and December at up to 83%, up from 75% in its September outlook. The strongest event on record peaked near 2.5 degrees Celsius in the winter of 1982-83. This year’s El Niño has not reached that level, but remains on an upward trend, according to NOAA. The seasonal climate pattern, marked by unusually warm water in the central and eastern tropical Pacific, can influence weather around the world. For California, it often shifts the Pacific jet stream south, increasing the odds of a wet winter, particularly in Southern California. NOAA’s latest seasonal outlook favors above-normal precipitation across the state, and a European forecasting model also signals a high likelihood of a wet winter. “There’s a 70 to 100% chance of a very wet winter across all of coastal California,” UC climate scientist Daniel Swain said during an online briefing, describing the European model’s forecast as an unusually strong signal. The risks extend beyond rainfall. Sea levels in San Francisco Bay have already been unusually high, National Weather Service meteorologist Dylan Flynn said. El Niño-related ocean changes are expected to combine with sea-level rise driven by climate change, a marine heat wave, storm surges and high tides, raising the potential for coastal flooding and erosion. “Every couple inches of sea level rise doubles the risk in California in terms of flooding,” said Patrick Barnard, who directs research at UC Santa Cruz’s Center for Coastal Climate Resilience. “Everything’s lining up to be a very risky winter for sure.” California has begun preparing. Gov. Gavin Newsom declared a state of emergency in September and directed state agencies to start readying communities. The need for preparation is heightened by the possibility that heavy rain and elevated coastal water levels could coincide, though seasonal forecasts cannot determine exactly when or where individual storms will hit. The event is also unfolding in a warmer world than earlier major El Niños, said Alexander Gershunov, a research meteorologist at UC San Diego’s Scripps Institution of Oceanography. NOAA has adjusted its El Niño metrics to account for the warming ocean, he said. “It is occurring in a warmer world than all the previous ones,” Gershunov said. “Let’s just see how it keeps evolving.”