This year’s El Niño—its so-called “Godzilla” strength only matched by the media frenzy around it—has the potential to bring above-average rainfall to the Bay Area this winter. “It’s possible that we could see the strongest El Niño ever observed,” said Daniel Swain, a climatologist at Stanford University. These wet-weather events occur every two to five years and are characterized by shifting trade winds and warmer-than-average sea-surface temperatures in specific areas of the Pacific Ocean. The current El Niño, already in effect, has been credited with bringing rain and alleviating drought conditions in states like Texas, along with spurring droughts in other places like Thailand. Last week, the National Oceanic and Atmospheric Administration announced that the weather pattern is gaining strength and almost certain to last through the winter and spring. In order to be considered strong, sea-surface temperatures in the tropical Pacific need to remain two degrees Celsius above average for three months or longer. Weak or moderate El Niños don’t have a strong track record for bringing winter rain to California, Mr. Swain said. But strong events are a more likely harbinger of much-needed rains, although they can also spur flooding and mudslides. These conditions can be exacerbated by current wildfires, which can make the ground virtually impenetrable. West Marin was hit with devastating floods during the 1982-1983 El Niño, which brought roughly 50 to 80 percent more rain to the state than usual. “It was just a relentless series of storms hitting the coast,” said Michael Anderson, the state climatologist with the Department of Water Resources. But rains aren’t 100 percent guaranteed. Mr. Anderson noted that the winds will be key: if a jet stream in the Pacific shifts south, as typically happens with El Niño, it is likely to push storms straight into California this winter—but the jet stream could split in two, leaving California dry. The effect of the so-called “Pacific blob,” a separate area of warm water in the northeastern Pacific, on El Niño is not really known, Mr. Anderson said.