Scientists warn of 'Quad Tides' flooding threat this winter Play

Malibu may be in a coastal flood watch today for some puny waves on top of a medium-high tide. But just wait until Thanksgiving and Christmas.

The California coast is going to get slammed this winter during those holidays. And not just by the super El Niño, but by an unlucky combination of other high tides.

Call it the Quad Tides.

Oceanographers at the University of California say there is a quadruple threat this winter:

1. The record El Niño sending waves our way.
2. Huge Pacific storms fed by the super-warm ocean, causing heavy rain.
3. Ocean surface elevations that have not been this high in the history of humanity.
4. Changing ocean currents that are shoving water against the California coast.

And all of this is going to culminate in two periods, three days each: the three days before Thanksgiving, and the three days bracketing Christmas.

Mark Merrifield is an oceanographer at Scripps.

"The El Niño is on top of a general sea level rise," Merrifield said. "And they are getting higher and higher as time goes on because there is a general trend in sea level as it continues to rise. So we're expecting likely the highest sea levels ever recorded on the California coast associated with this event."

And there's more bad news from the University of California. Meteorologist Daniel Swain:

"For an event that is as strong as the one that is currently being predicted for the one this year, it is going to significantly shift the odds in favor of a particularly wet winter, especially in Southern California," Swain said. "Also, increased Pacific Ocean sea levels that will likely affect and increase the likelihood of coastal flooding, particularly during strong storm events, or King Tide events. And it could potentially increase the risk of significant flooding in California later this winter."

There's another factor at play. High waves. Big surf. Turns out that's on a multi-year cycle as well.

Again, Mark Merrifield, an oceanographer at Scripps:

"It is a sort-of unlucky coincidence — the tidal cycle is also going to be at a peak around the end of this year," Merrifield said. "So tides tend to vary over long periods of time — 18.6 years and 4.4 years. We're at the peaks of those cycles, and around Christmastime we are going to be seeing some strong, strong tides — super tides, King Tides — that will superimpose on this rising sea level and the El Niño event to give us very high sea levels."

When will those king tides arrive? The timing couldn't be worse. The highest tides are predicted for the three days immediately preceding Thanksgiving and the three days right in the middle of the Christmas holiday: December 24, 25 and 26.

You might notice that we haven't talked about big swells and big waves on top of all this yet. Well, the oceanographers are worried about that as well.

Again, Mark Merrifield at UC San Diego's Scripps Institution:

"The other thing that's fairly certain with El Niño is that we are going to see high waves," Merrifield said. "It's not exactly clear where on the coast we're going to see these arrive, but usually it's on the entire California coast as the storm track is perturbed by the El Niño. So on top of the high level, high waves coming at us this winter. That combination — high waves, high sea levels, high tides, and as Dr. Swain mentioned, high rainfall — will contribute to considerable coastal flooding, intrusion of saltwater into the groundwater, and coastal erosion."

Again, the highest tides coming at us this autumn and fall will be the three days before Thanksgiving, and the three days bracketing Christmas.

Happy holidays.