The National Weather Service said on Thursday the Pacific Ocean is getting warmer, which means the phenomenon known as El Nino is likely to develop this summer-- and continue into winter.
Could this finally end California's drought?
In the parched state, the likely return of El Nino is raising hopes that shrinking reservoirs will fill this winter. El Nino gained a reputation for bringing stormy wet weather in the winter of 1997-98 when so much rain fell that rivers overflowed and saturated cliffs gave way.
El Nino develops when the Pacific Ocean near the Equator warms and pulls the jet stream south.
"If that stays fixed -- which it did for example in '97-98 from November all the way through March and I think it was April -- then we get storm after storm after storm after storm," said meteorology professor John Monteverdi.
"We could use it," he said.
But California could be disappointed. Not all El Ninos are equal. The warmer the ocean, the stronger the El Nino.
"The caution is, some of our indications indicate a weak El Nino and some also indicate a strong El Nino," Monteverdi said. "But most indicate a moderate El Nino."
A moderate El Nino is less likely to break California's drought. But whale watchers in Southern California have seen indications the ocean is warming perhaps more than climate models suggest. Alisa Schulman-Janiger organizes an annual whale census.
"This year we're seeing odd fish, warmer temperatures and at least three species of whales we don't typically see," she said.
Last week she photographed a mother and baby Bryde's whale. Their usual habitat is warmer tropical waters.
"We should have a very interesting year," she said.
El Nino's potential impact goes well beyond California. It reduces the risk of Atlantic hurricanes. And it could bring a mild winter to most Northern states.