Sea surface temperature anomalies show plenty of warm water in the equatorial Pacific. It’s been enough to get an El Niño going. (earth.nullschool.net)
We’ve waited all winter for it to be announced, and it seemed it might not happen, but El Niño has officially developed.
This ocean-atmosphere cycle is known for altering weather patterns around the world, and forecasters had predicted it could arrive as soon as last fall. So Thursday’s declaration from the National Oceanic and Atmospheric Administration seemed like a long time coming,
This El Niño, unlike 2016′s powerhouse version dubbed “Godzilla,” is predicted to be relatively feeble. But NOAA says it is still likely to have some meaningful impact on the weather in the Lower 48.
“While the El Niño is expected to be weak, it may bring wetter conditions across the southern half of the U.S. during the coming months,” NOAA wrote in its news announcement.
On a much larger scale, this event may help push the planet toward one of its warmest years on record in 2019.
El Niño — meaning “little boy” for its typical development around Christmas — is the warm phase of the El Niño-Southern Oscillation (ENSO). It is characterized by warmer-than-normal sea surface temperatures in the central and eastern equatorial Pacific Ocean. A natural occurrence, it tends to bring increased precipitation to the West Coast and southern United States among other global impacts.
The ENSO phases compared. (NOAA)
El Niños are rated on a scale from weak to very strong, and this event falls on the low end of the spectrum. Before this winter’s event, the most recent El Niño was of the very strong or super variety, in the winter of 2015-16. That event followed a rather weak El Niño the winter before.
El Niño’s opposite phase is known as La Niña. This occurs when cooler-than-normal water gathers near the equatorial Pacific. Its influences typically lead to drier-than-usual conditions in the southern United States, with the focus of the moisture more often hitting the Pacific Northwest and the northern tier of the country.
This El Niño may distinguish itself by persisting into the summer and even extending into next winter. This would be rare, if it happens.
“La Niña events can often carry over through the summer, but El Niño events are much less inclined to do the same,” said Barb Mayes Boustead, an atmospheric scientist. “[Persistence] of a full El Niño through the warm season is rare.”
Aside from the back-to-back events spanning 2014 to 2016, the only other recent case of El Niño surviving for two full years occurred from 1986 to 1988, Mayes Boustead said. And that earlier event was rather weak.
Even though El Niño wasn’t officially declared over the past several weeks, precipitation patterns have often mimicked those of an El Niño across the United States. The tweet below from the Weather Channel’s Jessica Arnoldy, before the official El Niño announcement, shows the telltale enhanced precipitation across the southern United States.
Todd Crawford, chief meteorologist at the Weather Company, concurred that several characteristics of the weather this winter have been consistent with El Niño and listed them in a tweet.
In the coming weeks, the predicted above-normal precipitation across the South corresponds well with patterns seen in El Niño winters. That hasn’t necessarily been the case all winter, which may be partly attributed to the rather weak nature of this event. For instance, extensive precipitation and snow in the Pacific Northwest of late is perhaps more typical of La Niña.
Weather patterns can be affected by other atmosphere and ocean factors, aside from El Niño, especially when it’s weak. “[Some] of the above-normal precipitation this winter in parts of the West is related to subseasonal variability attributed to another climate phenomena, the Madden Julian Oscillation, rather than El Niño influences,” scientists at NOAA wrote.
But the extra heat in the tropical Pacific Ocean resulting from El Niño is likely to help boost global temperatures in 2019.
Even before Thursday’s announcement, the United Kingdom’s Met Office was predicting 2019 to end up the second warmest year on record, projecting an average temperature of 1.1 degrees Celsius above the 1850-1900 normal.
The major El Niño of 2015-16 ended up boosting 2016′s global temperature to 1.11 degrees C above that same normal, which made it the warmest year in recorded history.