Like a pot of water on a slow boil, El Niño conditions in the Pacific Ocean are continuing to intensify, scientists said Thursday, setting up a winter that could bring drenching rain to some parts of California — at amounts potentially double the historical average, particularly in January and February.

On Thursday, scientists at NOAA, the National Oceanic and Atmospheric Administration, said there is a 100% chance of a strong El Niño being present from now through March, and an 83% probability that it will rank as the strongest in history since modern records began in 1950, up from 69% two months ago.

“We are seeing a lot of warmth in the tropical Pacific, which provides ample energy for storm systems as we move through the fall and winter,” said Michael Anderson, state climatologist with the California Department of Water Resources. “Be ready for the storms and watch those forecasts.”

Currently, surface waters in the Pacific Ocean along the equator are hotter than ever recorded for this time of year, roughly 5.8 degrees Fahrenheit warmer than average. Some subsurface areas in the eastern Pacific are a stunning 18 degrees warmer than average.

State officials said Thursday that in preparation for potentially major storms, flooding in coastal and inland areas, power outages, and mudslides that could begin next month and peak early in the new year, they have moved sandbags, rocks to rebuild levees and other equipment into vulnerable parts of the state.

Gov. Gavin Newsom announced that California is deploying swift water rescue vehicles, boats and specialized equipment to 13 local fire departments across the state to have in place before storm season starts.

“The time to prepare is now, with only weeks left until the first winter storms develop,” said Patrick Barnard, research director for the UC Santa Cruz Center for Coastal Climate Resilience. “Where we get the most intense rainfall events is difficult to predict, but there is high certainty that the California coast will experience the impacts of historically unprecedented elevated sea levels, as well as very large waves, acute beach loss, and extensive flooding in low-lying coastal communities throughout the winter.”

El Niño conditions occur every two to seven years when ocean waters along the equator off Peru become warmer than normal. The warmer waters affect weather patterns across the globe, causing more rain than normal in some parts of the world and severe droughts in others.

They begin when trade winds that normally blow from the east to the west weaken or reverse, preventing cold, deep-ocean water from rising to the surface. The warmer surface waters become, the stronger the El Niño is considered. The opposite — a cooling of the ocean waters off South America — is called “La Niña.”

El Niño events last for months and can often change the movement of the jet stream, pumping heat and moisture into the atmosphere and creating conditions that allow more winter storms to come to California, particularly Southern California — but also sometimes soaking the Bay Area and Sierra Nevada.

Although El Niño events do not guarantee wet winters in California, they increase the chances. To be sure, they occasionally fizzle out, as in 2015-16. But some of California’s wettest winters, including 1982-83 and 1997-98, have occurred during strong El Niño winters.

Because of the record-breaking nature of this year’s event, the odds are dramatically shifting toward a wetter-than-normal winter all across the state, said Daniel Swain, a climate scientist with UC Davis.

“We expect this strong event to become even stronger and possibly the strongest on record by a wide margin,” Swain said. “We are going from probably to likely toward a wet winter, with potential coastal and inland flooding and other challenges.”

New supercomputer model runs from European atmospheric researchers now show an 80% to 90% chance that rainfall totals on most of California’s coast — from the Bay Area to San Diego — will rank among the wettest 10% of the historical average from January to March.

When averaged out, the 51 model runs show 165% of normal rainfall is expected for Northern California from January to March. Over the same period, 194% of normal rainfall is expected for Central California, and 226% of normal rainfall for Southern California, according to data from the European Centre for Medium-Range Weather Forecasts, a weather organization based in England and funded by more than 20 nations.

Caroline Thomas Jacobs, director of the California Office of Emergency Services, said her agency is holding meetings with cities, counties, other state agencies and emergency responders to plan out various winter scenarios. She recommended people visit ready.ca.gov for information and to sign up for the emergency alert system their county provides.

“We want to be prepared,” she said. “We always err on the side of being prepared.”

Although significant rain or snow is not likely for at least a month, the impacts of El Niño have been increasing already for the past few months. Due to the warm Pacific Ocean, numerous hurricanes have occurred off Mexico and Hawaii. The remnants of several have caused heavy waves and coastal erosion in Southern California.

In recent weeks, 10 homes were damaged so badly they were red-tagged along the beach in Dana Point, a sinkhole opened near homes in Malibu, and high tides and storm waves have repeatedly overtopped railroad tracks in San Clemente that are used by Amtrak and other agencies, causing emergency closures.

Tropical marine species, from blue marlin to manta rays to sea turtles, have been spotted off Southern California beaches.

In the Bay Area, the National Weather Service issued a flood advisory from 9 a.m. Friday to 3 p.m. Tuesday for waterfront locations along the San Pablo Bay, San Francisco Bay and Monterey Bay, warning of minor flooding. More severe coastal flooding could come over Thanksgiving, Christmas and Martin Luther King Jr. Day as high tides known as “king tides” combine with warmer ocean waters, which expand and cause higher sea level, experts say.

Added to that is a Kelvin wave — a massive, slow-moving pulse of warm water under the ocean’s surface that is moving up the West Coast due to wind and water circulation changes from the El Niño. The current Kelvin wave adds about 6 to 12 inches to the sea level height off California.

Low-lying places like Alviso, the Embarcadero in San Francisco, parts of the bay shoreline in Marin County and some beaches in Santa Cruz could see more water than normal, forecasters say.

As sea levels around the world continue to rise due to climate change, this year’s El Niño offers a glimpse of things to come, according to some experts.

“Extreme conditions like we’re seeing this year might become more common in the future,” said Madeline Cavalieri, deputy executive director of the California Coastal Commission. “This really gives us an opportunity to prepare for that future, a preview of what we’ll be experiencing more regularly.”

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