There’s a good chance you’ve heard about the likelihood of the La Niña weather pattern returning over the next few months, pushing the jet stream north and impacting weather across North America. But a different pattern in the Atlantic is on the verge of development, an Atlantic Niña, and while it’s unlikely to impact North American weather patterns, it’s still worth understanding.

While El Niño and La Niña are the result of changes in trade winds across the Pacific, Atlantic Niña and Atlantic Niño are the different phases of the Atlantic zonal mode climate pattern. According to NOAA, this pattern traditionally swings between warm and cold phases year by year, with the eastern equatorial Atlantic usually showing a rather strong seasonal cycle in surface temperatures. The temperatures reach their warmest around March and April and swing back to the coldest between July and August.

The colder water, described as a “cold tongue” along the equatorial Atlantic, is caused by southeasterly winds which pull warmer water on the surface away from the equator, bringing the colder water to the top. When that cold tongue is colder than usual, that’s considered an Atlantic Niña. When the cold tongue is warmer than usual, that’s an Atlantic Niño.

“The exact definitions vary, but typically, 3-month averaged sea surface temperature anomalies in the eastern equatorial Atlantic have to exceed ±0.5 degrees Celsius (± 0.9 degrees Fahrenheit) for at least two overlapping seasons in order to qualify as an Atlantic Niño or Niña.“

2024 began with the strongest warm event since 1982, with temperatures from February to March exceeding 30 degrees Celsius (86°F). But a never before swing back to cold has occurred between June/July, surprisingly coinciding with a weakening of southeasterly trade winds near the equator. Scientists are currently unable to explain the shift, but they’re searching for answers.

So how does this ±0.5 degrees Celsius (±0.9°F) change in temperature really impact the environment? Much like traditional El Niño and La Niña, it has a lot to do with rainfall. The Sahel region of Africa tends to see a reduction in rainfall, while the Gulf of Guinea tends to see an increase. Plus northeastern South America sees a seasonal shift in the rainy season, and powerful hurricanes near the Cape Verde Islands tend to be more likely.

The Atlantic Niña hasn’t quite developed yet, but it’s on the verge. Scientists with Climate.gov (NOAA) intend to keep a close eye on the Atlantic to see what happens over the next several weeks and, if it does develop, how it impacts the world around us.

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