La Niña Subsiding, Atlantic Climate Phenomenon Forming

This map, updated weekly, shows the cooler-than-normal sea-surface temperatures (blue) in the equatorial Pacific over the last month that define La Niña. Click on the chart to go to see the most recent version in the IRI Data Library.

A unique climate phenomenon is forming as a more familiar one weakens. At this month’s climate briefing, forecasters from the International Research Institute for Climate and Society (IRI) discussed each of these in detail.

First the one you likely know a little about. Tony Barnston, IRI’s lead forecaster, said this year’s strong La Niña is in the process of subsiding for now. Ocean temperatures in the eastern equatorial Pacific continue to warm, though they are still roughly a degree Celsius cooler than normal. By the end of April, temperatures are expected to return to near normal.

Barnston noted that though the sea surface temperature (SST) anomalies continue to weaken, the atmospheric conditions associated with La Niña are still quite strong. They’ll likely remain that way for at least the next month or two, increasing the likelihood of wet weather in Australia, cooler than normal temperatures in the Pacific Northwest and other impacts associated with La Niña during that time.

This map, updated weekly, shows the warmer-than-normal sea-surface temperatures (red) off the coast of Angola and Namibia over the last three months that define a Benguela Niño. Click on the chart to go to an interactive, updated version in the IRI Data Library.

Brad Lyon, a research scientist at IRI, also highlighted a lesser-known climate phenomenon occurring in the southeastern Atlantic. The phenomenon is known as a Benguela Niño. A slackening of alongshore winds possibly accompanied by the southward movement of waves called Kelvin waves leads to the southward migration of warm water from the equator to off the coast of Namibia and Angola. Lyon noted, “the relative roles of Kelvin waves versus local wind anomalies [is] still an open area of investigation.”

This map, updated weekly, shows the above normal precipitation in Angola and Namibia for the last three months caused in part by the Benguela Niño. Click on the chart to go to an updated version in the IRI Data Library.

On average the phenomenon occurs about once a decade. The last strong Benguela Niño occurred in 1995. Just as El Niño can lead to increased rainfall in Peru, so a Benguela Niño can lead to increased rainfall in Namibia and Angola. Precipitation in the region from December through February shows just such a pattern.

For a more in-depth look at IRI’s La Niña forecast, visit IRI’s ENSO resources page. More on the causes of the Benguela Niño can be found in this October 2010 paper from Geophysical Research Letters.