What does El Niño mean for San Mateo County? It could be the strongest on record, but experts say wait and see for the Bay Area 

Typically, the push of warmer water toward the West Coast of the Americas, which is generated by weakened trade winds, means that the southern third of California gets a wetter fall and winter and the northern third of the state has a drier season, Merchant said. 

In California’s middle portion, where San Mateo County is situated, El Niño isn’t as strong of a predictive tool, however, NWS meteorologists said previously it favors a slightly wetter winter. 

“In the middle third, we basically there’s no signal either way,” he said. “We’ve had both. We’ve had both dry conditions during El Niños and above normal precipitation during El Niños and strong El Niños. So the signal for our area is actually pretty weak.” 

Although the area’s atmosphere has been more moist than usual in the summer season, Merchant was reluctant to say that could mean anything for the upcoming winter. An increase in atmospheric rivers and heavy rain will be the real indication, he said 

“If we start seeing really strong atmospheric rivers, one after another, then that will give us confidence that we’re being impacted in that way,” he said. 

The National Weather Service isn’t using the “super” El Niño qualification that’s already been colloquially given to the weather pattern, though there’s a 97% chance it will extend through the spring of 2027 and an 81% it’s going to be a very strong El Niño. Given the temperature recordings, Merchant said there are indications it will be one for the books. 

The stronger an El Niño is, the more likely it is to bring extreme and disruptive weather events worldwide. 

“We already have indications that this is going to be the strongest on record, given that we already have recorded the highest water temperatures,” Merchant said.