There’s a baby girl gestating in the womb of the equatorial Pacific Ocean, and if she’s born without complication, she’ll make a big impression all around the world.
I’m speaking of the La Niña climate phenomenon. And according to the latest forecast, she stands a 69 percent chance of being born between July and September, pushing aside the almost dead 2023-2024 El Niño. (A new forecast is coming soon.) You can see her developing along the equator in the screenshot above, and in this video:
The animation is based on sea surface temperature data gathered by the GOES-18 satellite between April 13 and May 31, 2024. The telltale sign of La Niña’s gestation is the spear of green that elongates and widens toward the west from the coast of South America. The green shows the emergence of relatively cool waters along the equator — a hallmark of La Niña.
What’s Going on, and Why Should We Care?
La Niña is likely to be in the news quite a lot in coming months, so I thought it would be helpful to offer a little review of her essential character, and what we might expect of her.
In Spanish, “La Niña” means “the girl.” (We’ll get to that naming in a minute…) It’s the opposite of “El Niño,” and together they make up a phenomenon called the El Niño-Southern Oscillation, or ENSO. They are characterized by shifts in the temperature of sea surface waters along the equator in a region west of South America. La Niña comes with cooler than average sea surface waters, whereas El Niño brings the opposite.
This illustration shows atmospheric circulation between December and February during a La Niña. It also includes a map of sea surface temperature anomalies. Blue-green colors in the central and eastern equatorial Pacific Ocean show cooler than normal temperatures. These tend to inhibit thunderstorms. In the western Pacific, warm temperatures, shown in orange, do the opposite: They juice up thunderstorm activity. This atmospheric circulation pattern drives impacts to weather around the world. (Credit: NOAA Climate.gov drawing by Fiona Martin.)
Although these temperature shifts are relatively small, they usually have significant and far-reaching impacts on weather. During a La Niña, rising moist air along the equator in the western Pacific is enhanced, juicing up thunderstorm activity. By contrast, the thunderstorm activity shifts toward the central and eastern Pacific during an El Niño.
These shifts give a shove to atmospheric circulation, changing how heat and moisture is carried out of the tropics toward the mid-latitudes. In turn, this disrupts the mid-latitude jet streams that usher weather systems across far-flung parts of the globe, resulting in changes to temperature and precipitation patterns.
California offers a recent example. Over the past couple of winters, the El Niño that’s currently ending helped bring copious moisture to the drought-plagued Golden State. Now, with La Niña’s likely arrival, Californians should bet on the opposite. (But in the weather casino, there are no guarantees.)
During La Niña, the jet stream racing east across the Pacific Ocean often meanders far to the north and is less reliable across the southern tier of the United States. Southern and interior Alaska, and the Pacific Northwest, tend toward cooler and wetter conditions than average. The southern U.S. tier — from California to the Carolinas — typically trends warmer and drier. Farther north, the Ohio and Upper Mississippi River Valleys may be wetter than usual. One caveat: other factors can favor different outcomes. (Credit: Climate Central. Caption material from Climate.gov)
After we get La Niña’s official birth announcement from the midwives over at the National Oceanic and Atmospheric Administration, I’ll write more about the specific impacts we might experience next winter. For now, check out the graphic above.
I’ll also just mention that forecasters are already predicting significantly more Atlantic hurricanes than average, and stronger ones too. This is thanks in part to La Niña’s far-flung impacts, as well as record-shattering ocean heat — hurricane fuel — in the Atlantic’s main development region for cyclones. (I’ll have more to say about this in my next post.)
What’s in a Name?
How did these phenomena get their names? We can thank Anchovy fishermen plying the coastal waters of South America for that. In the early 1970s, they realized that something, well, fishy, was happening. More specifically, in some years they saw their catch plummet.
Their ill fortune turned out to be linked to a combination of over-fishing plus unusually warm surface water appearing around Christmas time. Through an unfortunate cascade of ecological impacts stemming from the warmer water, their nets were left all but empty.
In Spanish, “El Niño” refers to the Christ Child, and since these impacts were happening around Christmas, that’s the name that stuck for the phenomenon. And “La Niña,” or “the girl child,” became the moniker for its opposite.
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