There’s a 57% chance this will be a moderate La Nina and only 15% that it will be strong, said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. He said it is unlikely to be as strong as last year’s because the second year of back-to-back La Ninas usually doesn't quite measure up to the first.
This La Nina is expected to stretch through spring, Halpert said.
WHAT DOES THIS MEAN FOR THE WEST?
For the entire southern one-third of the country and especially the Southwest, a La Nina often means drier and warmer weather. The West has been experiencing a two decade-plus megadrought that's worsened the last couple of years.
But for the Northwest — Washington, Oregon, maybe parts of Idaho and Montana — La Nina means a good chance rain and drought relief, Halpert said.
“Good for them, probably not so good for central, southern California,” Halpert said.
The Ohio Valley and Northern Plains could be wetter and cooler. La Nina winters also tend to shift snow storms more northerly in winter while places like the mid-Atlantic often don’t get blockbuster snowstorms.
WHAT ABOUT ATLANTIC HURRICANE SEASON?
During last year’s La Nina, the Atlantic set a record with 30 named storms. This year, without La Nina, the season has still been busier than normal with 20 named storms and only one name left unused on the primary storm name list: Wanda.
The last couple weeks have been quiet but “I expect it to pick up again,” Halpert said. “Just because it’s quiet now, it doesn’t mean we won’t still see more storms as we get later into October and even into November.”
La Ninas tend to make Atlantic seasons more active because one key ingredient in formation of storms is winds near the top of them. An El Nino triggers more crosswinds that decapitate storms, while a La Nina has fewer crosswinds, allowing storms to develop and grow.
WHAT ABOUT THE REST OF THE WORLD?
Much of both southeast Asia and northern Australia are wetter in La Nina — and that’s already apparent in Indonesia, Halpert said. Central Africa and southeast China tend to be drier.
Expect it to be cooler in western Canada, southern Alaska, Japan, the Korean peninsula, western Africa and southeastern Brazil.
Follow Seth Borenstein on Twitter: @borenbears.
The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.
FILE - In this Wednesday, Sept. 1, 2021 file photo, floodwaters slowly recede in the aftermath of Hurricane Ida in Lafitte, La. On Thursday, Oct. 14, 2021, the National Oceanic and Atmospheric Administration announced that a La Nina has formed, which can be bad news for parts of the parched West. It also could mean a more active Atlantic hurricane season. (AP Photo/Gerald Herbert, File)
Credit: Gerald Herbert
Credit: Gerald Herbert