As summer turns to fall, the El Niño conditions brewing in the Pacific Ocean continue to grow, increasing the chances of a wet winter in drought-stricken California, federal scientists reported Thursday.
There is now a 95 percent chance that El Niño conditions will continue through the end of this year — up from 85 percent in June and 50 percent six months ago.
“Things are continuing to evolve. We are one month closer to the point where we should see impacts this winter. Obviously our confidence is increasing,” said Mike Halpert, deputy director of the National Oceanic and Atmospheric Administration’s Climate Prediction Center in College Park, Maryland.
Water temperatures in the Pacific Ocean this week along the equator are 3.78 degrees Fahrenheit above the historic average, federal scientists announced in their monthly El Niño update. That’s the warmest temperatures during the first week of any September since 1997, a year that saw drenching winter storms in the Bay Area and California.
El Niño is a disruption in the weather patterns over the Pacific Ocean, when the ocean’s surface warms more than normal. Those warm waters release heat, changing wind directions and the jet stream.
Strong El Niños, which occur when the Pacific Ocean is the warmest, have historically been linked to wet weather in California and South America, and droughts in Australia and Asia. Last month, NOAA, the parent agency of the National Weather Service, reported that water temperatures, wind conditions and other factors showed El Niño conditions that were “significant and strengthening.” This month, they were upgraded to “strong.”
Since 1951, there have been five winters with strong El Niño conditions, meaning ocean water at the equator that is at least 2.7 degrees Fahrenheit warmer than normal. In four of those winters — 1957-58, 1972-73, 1982-83 and 1997-98 — rainfall in the Bay Area and Los Angeles was at least 140 percent of the historic average, according to studies by Jan Null, a former National Weather Service forecaster who owns Golden Gate Weather Services in Saratoga.
But there is no ironclad guarantee. In 1965-66, a strong El Niño didn’t deliver above-average rain. It simply fizzled out.
In 1997-98, trade winds that normally blow east-to-west across the Pacific, holding back warm water, stopped and reversed direction, pushing more warm water toward North and South America. Although that has happened at times this year, the pattern isn’t as strong.
Also, for storms to help really fill the big reservoirs in Northern California, such as Shasta, Oroville and Folsom, in a steady, consistent way, the state will need cool enough winter temperatures to build a big Sierra snowpack, something that is not guaranteed, particularly as the climate continues to warm.
“That’s really an open question,” Halpert said.
Already, cities around the state are preparing for potential soaking storms and even flooding and mudslides, and roofers and tree trimmers are booked solid with business from concerned residents. But this week, authorities stepped up efforts to tamp down expectations, fearful that if people stop conserving water and this winter doesn’t bring consistent, soaking storms, the fifth year of the drought next year will be even more dire.
“Current El Niño conditions cannot tell us how many storms may cross California this coming winter or how much rain and snow will fall in our state,” said Mike Anderson, California’s state climatologist with the Department of Water Resources.
“The fact is that this coming winter could extend our record-dry weather or bring major storms, heavy precipitation and coastal storm surges or a combination of all,” he added. “We must prepare by conserving water in our daily lives, as well as protecting property against the potential of heavy storms and local flooding.”
Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN