LOS ANGELES -- Hurricane Rachel, currently spinning out in the Pacific Ocean, is expected to raise the risk of coastal flooding in Southern California and could bring widespread rain to the region at some point this weekend and early next week.

Forecasters are warning that south-facing beaches such as the Long Beach Peninsula, Catalina Island and the coastline from Malibu to Ventura could be particularly at risk of flooding on account of Rachel, the latest named entrant in an unusually active, El Niño-fueled hurricane season.

Also contributing to the flood risk is the arrival of a Kelvin wave, another feature of El Niño that can raise sea levels by 6 to 12 inches. The higher the seas, the greater the threat for California’s coastline.

The risks of coastal flooding is expected to peak Sunday, said Ryan Kittell, a meteorologist with the National Weather Service office in Oxnard.

“It seems pretty likely that we’re going to have an additional round of significant beach erosion, especially in that Sunday time period,” Kittell said. “And some of those areas have already been impacted by the coastal flooding events and are really vulnerable, without much beach left.”

Tides in Southern California are expected to be 1 foot to 1.5 feet above what would ordinarily be expected without the abnormally warm ocean temperatures wrought by El Niño.

“We could see — it’s on the table — some isolated damage issues,” Kittell said, but perhaps less dramatic than Labor Day weekend, when some homes in Malibu, Long Beach and Dana Point were heavily damaged by swells from Hurricane Marie.

And all this comes as forecasters say odds are increasing that this El Niño will be the strongest in the modern record, which goes back to 1950.

Here’s what you need to know:

Hurricane Rachel

Rachel, which was a Category 1 hurricane on Wednesday, is expected to continue weakening as it moves closer to Southern California, according to the National Hurricane Center.

The storm has been moving northwest, but is expected to make a sharp turn to the right sometime Thursday or Friday, due to a “fairly complicated scenario where we have two abnormal low-pressure systems ... dropping down from the north and will be over the California area sometime between [Thursday] and early next week,” Kittell said.

“They’re going to interact with the remnants and leftovers of Rachel, especially its moisture, and kind of form a new system that’s going to move over our area,” he added.

The odds the system will still be at tropical storm strength by the time it hits Southern California are considered very low, forecasters say.

Rain on the way?

“Right now, it seems like Sunday night through Monday is the time period with the highest chances for rain,” Kittell said.

There’s a 70% to 90% chance that rain will fall at some point between Saturday and Tuesday in L.A. and Ventura counties, Kittell said, with the highest chances between Sunday night and Monday night.

For those running the 2XU Long Beach Marathon Sunday morning, Kittell said he expects a 40% to 50% chance of rain during the day.

“So you can be optimistic and hope for no rain, but certainly those chances are high enough to at least plan for some light rain at some time during that event,” Kittell said.

Not much rain is expected — perhaps one-quarter to three-quarters of an inch, with mountains getting a bit more. Rain rates are probably going to be a quarter of inch per hour or less, making debris flow and landslides unlikely.

For San Diego County, Orange County and the Inland Empire, the chance of rain is expected to increase Sunday through Tuesday, with the best odds Sunday and Monday, according to the weather service office in San Diego.

In the San Francisco Bay Area, forecasters warned of up to 1.2 feet of inundation above ground level “in low-lying areas near shorelines and tidal waterways,” the weather service office in Monterey said.

Gusty conditions ahead

Sunday is expected to be the windiest day, “with pretty widespread south-to-west winds, anywhere between 20 to 35 mph gusts,” Kittell said. “It doesn’t look like a great period to go boating.”

Forecasters also expect strong rip currents and dangerous waves, which increase the risk of drowning for people swimming at the beach.

“There is a low but present risk for some locally strong winds as well as a thunderstorm or two,” Kittell said, “coinciding with that coastal flooding risk is also some risk for some high surf and strong rip currents at the beaches.”

Adding to those concerns will be expected high tides, as well as the incoming Kelvin wave.

Kelvin wave

Fueled by El Niño, a “coastally trapped” Kelvin wave has been moving up the coast of the Americas for weeks, bringing with it hotter water and elevated sea levels. When combined with storm swells and high tides, Kelvin waves can increase the risk of coastal flooding.

Until recently, Kelvin waves were a pretty obscure concept. But they’re fundamentally at the heart of El Niño: a climate pattern in which the ocean waters in the central and eastern equatorial Pacific heat up and spur changes in the atmosphere that can affect weather around the world.

“Coastally trapped” means they must follow a coastal boundary, with the shoreline to their right in the Northern Hemisphere, said Michael Jacox, research oceanographer with the National Oceanic and Atmospheric Administration’s Fisheries’ Ecosystem Science Division.

The latest Kelvin wave is expected to keep sea levels raised for a while. The initial edge of the wave has probably already passed Los Angeles, and might even be north of San Francisco, Dillon Amaya, an assistant professor at North Carolina State University’s Department of Marine, Earth and Atmospheric Sciences, told The Times. More inundation is possible as the Kelvin waves pass through.

“I do think it is safe to say that sea levels will remain elevated for months,” Amaya said. “In fact, the data shows another El Niño-related coastally trapped wave already in transit from the tropics.”

That’s expected, as the last major El Niño spawned five to six such waves, Amaya said.

Part of the reason why Kelvin waves are becoming better known as a hazard has been the rise in sea levels over the decades due to human-caused climate change. Sea levels have risen by about one foot over the past 125 years along the California coastline.

El Niño

On Thursday, NOAA’s Climate Prediction Center said the chance of a historic, record-breaking El Niño is now 83%, up from the probability of 75% issued last month.

El Niño typically emerges every two to seven years, and the warming of ocean waters is coupled with changing conditions in the atmosphere, sparking changes in weather across the globe.

For Southern California, the strongest El Niños are typically associated with higher-than-average rainfall. Two of the strongest on record, in 1982-83 and 1997-98, saw very wet winters that left a trail of devastation in California.

That’s not always the case, though. During the 2015-16 El Niño season, California didn’t experience elevated rainfall, but did see record coastal erosion, another hallmark of the climate pattern.

Wide swaths of the Pacific Ocean are now at temperatures never seen before in the modern record. Scientists have observed temperatures underneath the sea surface greater than 18 degrees above the baseline.

“With an event of this magnitude, the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed,” the Climate Prediction Center said.

Heat

Southern California’s latest bout of extreme heat is expected to begin winding down Thursday or Friday, with the highs of 95 to 105 degrees that were common Wednesday tumbling down into the 70s by Sunday or Monday.

The heat will still be in force on Thursday, with forecast highs of 101 in Paso Robles, 100 in Woodland Hills, 99 in Santa Clarita; 96 in Burbank, Pasadena and Palmdale; 94 in downtown L.A., Thousand Oaks and Santa Ynez; and 92 in Long Beach. An extreme heat warning will be in effect for wide swaths of Southern California through Thursday evening.

There will still be a high risk for heat-related illness and large plume-dominated fires through Thursday, Kittell said.

“Limit outdoor activities to just the early morning hours,” the weather service said. “Stay in air conditioned spaces during the afternoon and evening hours.”

There are initial signs of more heat toward the end of next week and into the following week, according to Kittell.

“Right now, it doesn’t look nearly as extreme as what we just had, but it certainly does look elevated,” he said.

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