El Niño 2016

Sunset surfing at Scripps Pier. — Nelvin C. Cepeda / UT San Diego / Twitter @NelCepeda

UTSD

It’s not just El Niño coming to town.

That was the theme of a public discussion hosted this week by UC San Diego’s Scripps Institution of Oceanography in La Jolla, with in-house researchers and guest speakers from organizations such as the National Weather Service.

Scientists have warned that one of the most powerful El Niño systems in recorded history could pummel Southern California well into the spring.

Years of drought and record-high temperatures in the Pacific Ocean could complicate things further, scientists in this region said.

“It’s been a strange two years, a very strange two years,” said Dan Rudnick, an oceanographer at Scripps. “This El Niño is happening on top of the strange stuff we’ve had since 2014.”

If El Niño conditions pull more winter storms down to Southern California than usual — and that has been the historical pattern during years with a strong El Niño — the precipitation will likely move across some of the warmest ocean temperatures on record.

“Those warm waters off the coast can add moisture, can add instability. In other words, give us heavier rainfall rates as they move in,” said Alex Tardy, a meteorologist with the National Weather Service office in Rancho Bernardo. “We’ve already seen that a couple of times this year with the rainfall in early November.

“It’s timing, but there’s the potential for increased [coastal] flooding,” he said. A “double whammy,” he added, would occur if flooding from inland watersheds creates flooding, mudslides or other property damage.

In many places, drought conditions may have reduced vegetation and destabilized soils — making mudslides more likely. Scientists caution that repeated storms could swell rivers and small streams to areas that haven’t seen such conditions in decades.

Adding to concerns, warmer weather in the past year has contributed to recent tides well above predicted levels.

“What you see is a tendency for the observed tide to stand above the predicted tide by 8 inches or so,” said Dan Cayan, a climate researcher at Scripps. “That’s not been the case over the last couple of days, but once the atmosphere changes, we’re anticipating with that warmer water that we’ll probably pick up to anomalously higher sea levels.”

If a low-pressure system continues to move toward the region during the next few days, coastal areas could get hit hard by waves over Thanksgiving weekend, Cayan said.

“The largest tides this winter are the ones approaching us in the next week, so that’s an important period for us,” he said. “It turns out there’s a signature of a storm on the horizon.”

With roughly a century of data and just a handful of El Niño events on record, scientists were cautious not to talk in terms of guarantees. Only about half of such weather events have delivered strong precipitation to Southern California. The most powerful El Niño on record came during the winter of 1982-83.

However, given the convergence of unusual conditions this year, everyone in attendance at the Scripps forum Thursday expressed a strong curiosity for what the winter will bring.

“We don’t know what will happen next because it’s been such a strange couple of years, and we’ll see how this one evolves in comparison to past El Niños,” Rudnick said.

joshua.smith@sduniontribune.com, (619) 293-2234, Twitter: @jemersmith

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