NWS Says La Niña Has Ended, Likely Impact on Weather
On March 9, 2023, the Climate Prediction Center of the National Weather Service (NWS) announced that La Niña conditions which persisted for 3-years have finally ended. But we are not shifting directly into El Niño. Instead, we’re entering a transitional phase. NWS expects neutral conditions to continue through the Northern Hemisphere into spring and early summer of 2023.
La Niña and El Niño represent opposite phases of what meteorologists call ENSO, the El Niño Southern Oscillation in the Pacific Ocean. They govern recurring climate patterns across the tropical Pacific and have a cascade of global side effects, says NWS.
The patterns shift back and forth irregularly every two to seven years. This past La Niña phase lasted three years, an unusually long time.
NWS predicts that ENSO-neutral conditions will continue through the spring. The weather service also predicts El Niño conditions to form during summer 2023 and persist through the fall.
Impacts on Weather
The oscillation brings predictable shifts in ocean surface and atmospheric temperatures. These shifts disrupt the wind and rainfall patterns across the tropics.
El Niño brings cooler, wetter conditions to the southern U.S. in winter months. It also brings stronger steering currents that can disrupt low-pressure systems coming off the coast of Africa that turn into hurricanes.
La Niña, on the other hand, usually means less disruption, more Atlantic storms, and deeper droughts in the southern U.S. But we’re finally putting the most recent La Niña behind us.
ENSO Influence on Atlantic and Pacific Hurricane Seasons
The continental United States and Caribbean Islands have a substantially decreased chance of experiencing a hurricane during El Niño and an increased chance of experiencing a hurricane during La Niña. These maps (by NOAA Climate.gov, based on originals by Gerry Bell) explain why.
Overall, El Niño contributes to more eastern and central Pacific hurricanes and fewer Atlantic hurricanes. Conversely, La Niña contributes to fewer eastern and central Pacific hurricanes and more Atlantic hurricanes – exactly the opposite.
Other Influences on Hurricane Formation: AMO
NOAA also says that other oscillations, such as the Atlantic Multi-Decadal Oscillation (AMO) also influence hurricane formation. The warm phase of the AMO is associated with warmer sea surface temperatures and high hurricane activity in the main development region of the Atlantic between Western Africa and the Caribbean.
“The hurricane activity in any given season often reflects a combination of the multi-decadal signals and ENSO,” says NOAA.
For More Information
For a fuller discussion of how El Niño and La Niña influence other aspects of weather worldwide, check out NOAA’s Climate.gov, especially the FAQ page.
Also, the Associated Press ran an interesting story this morning by Seth Borenstein. The headline: “La Nina, which worsens hurricanes and drought, is gone.”
Borenstein says NOAA gives El Niño a 60% chance of returning this fall. But there’s also a 5% chance that La Niña will return for an unprecedented fourth winter.
We should have more certainty in a few months.
Posted by Bob Rehak on 3/9/23
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