El Niño has a little brother: How it affects storms

AUSTIN (KXAN) — It turns out there’s more than one Niño impacting our weather. According to scientists at the National Oceanic and Atmospheric Administration, or NOAA, they’re increasingly researching a phenomenon known as “Atlantic Niño” which may have a major impact on certain hurricanes in the Atlantic Ocean.

Meteorologist Nick Bannin spoke with NOAA Oceanographer Hosmay Lopez about their findings so far.

KXAN Meteorologist Nick Bannin: Hosmay, some of your research has pointed to the importance of Atlantic Niño. Can you explain what that is?

Hosmay Lopez, Oceanographer with NOAA: Atlantic Niño is a version of [the] El Niño that occurs in the Pacific… it is known as El Niños little brother. Little brother, because it’s usually smaller than the well known Pacific Niño and because the Atlantic basin is smaller, geographically speaking, and the dynamical aspects of the Atlantic are not as strong as those in the Pacific so that Atlantic Niño could be viewed as a smaller little brother of the Pacific Niño and the physical mechanisms responsible for such events are very similar between the two basins.

Bannin: What part of the Atlantic are you specifically focusing on for this Atlantic Niño?

Lopez: The Atlantic Niño occurs, just like in the Pacific, it strides the equator. The way it manifests itself is through sea surface temperature anomalies. So when we have an Atlantic Niño, you have warmer than normal equatorial temperature anomalies in the ocean surface. And when you have an Atlantic Niña, which is the opposite phase, you have a cold anomaly in the tropical Atlantic, mostly near the coast of Africa, but extends westward and approaches the coast of South America.

Bannin: How does the phase of Atlantic Niño or Niña impact hurricane development in the Atlantic?

Lopez: Just like you mentioned, we have a study this year that was published in the journal ‘Nature Communications,’ that shows that Atlantic Niño could be thought of as a new predictor, if you will, of seasonal hurricane activity in the Atlantic. For example, before this study, most of the seasonal predictions rely on the Pacific El Niño and also on tropical Atlantic sea surface temperature. But now we show in this new study that Atlantic Niño could be thought of as a new predictor, because dynamically speaking and physically speaking it behaves differently and independently from the other events that I mentioned. For example, they behave differently from the Pacific counterpart. So we get [to] hopefully add more knowledge and more information if we know this current state of the Atlantic Niño and if we can predict it. And I want to mention that Atlantic Niño is very well predicted a few months ahead of the hurricane season. And other aspects that separates Atlantic Niño from the Pacific counterpart is that Atlantic Niño usually peaks during the boreal summer months, June, July, August, right in the middle of the Atlantic hurricane season. So you have a very direct impact to hurricane formations there.

Bannin: Is it the warm phase of the Atlantic Niño that gives way to more hurricanes or the cool phase?

Lopez: It is that warm phase, as opposed to the Pacific El Niño where the warm phase produces less hurricanes in the Atlantic basin through increasing vertical wind shear through teleconnections. The Atlantic Niño warm phase produces more hurricanes and those hurricanes that are usually related to Atlantic Niño are those that forms along the Cape Verde Islands, right off the coast of Africa. Those are responsible for about 70 to 75% of the hurricanes that reach major categories in the Atlantic basin. So Atlantic Niño proved to be very important for those big big hurricanes that obtained very strong categories and also that persist for over a long time, because there’s basically open oceans for these hurricanes that formed off of Cape Verde Islands to propagate westward towards North America and perpetually grow and have a big impact in in the Caribbean as well as North America.

Bannin: What phase of Atlantic Niño are we in now?

Lopez: Right now it’s fairly neutral. So this year is fairly neutral. We had one of the biggest Atlantic Niño events in 2021. That was a major Atlantic Niño event, but right now it’s currently neutral conditions in the equatorial Atlantic, although I have to stress out that north of the equator in the tropical Atlantic, where we call this region, the main developing region (MDR), for hurricanes, that’s different from the Atlantic Niño region. This main development region is record warm at the moment.

Bannin: It’s an interesting dichotomy there, because given how warm parts of the Atlantic are, you would think that the, the Atlantic Niño would be in a positive phase, but you take it down to the equator in that Atlantic Niño region, and you know, it’s in that average range.

Lopez: Correct. Actually, what we’re mentioning here are what we call modes of natural variability. These are preferred states that the ocean and the atmosphere resides, for example, Atlantic Niño is one of them. The Pacific Niño is another one, we also have another mode, that’s called the Atlantic Meridional Mode. And why we call it meridional? Because it’s a north/south dipole, if you will, of sea surface temperature anomalies where you have, for example, in the northern hemisphere, you have warmer anomalies and in the southern hemisphere, you have colder anomalies. So these sea surface temperature anomalies are by no means coherent throughout the globe.

Bannin: In a neutral phase of Atlantic Niño does it just not have as much of an impact either way on what’s happening in the Atlantic and then you start to focus more on what El Niño is providing or the regular sea surface temperatures of the tropical Atlantic?

Lopez: That that’s correct. In a neutral phase, it’s basically we have no event. So we either have an Atlantic Niño, or an Atlantic Niña, which is a cold phase. If it’s neutral, there’s no predictable signal, if you will, so we cannot assess any impacts from a neutral phase. That’s what we call climatology. So we have to we have to depend on other factors. For example, this year, we’re depending a lot on the very strongly warm North Atlantic north of the Atlantic Niño region and also the presence of the Pacific Niño. They counteract each other, because now both basins are warm. So we have a warm Pacific, which tends to decrease hurricane activity in the Atlantic, but also we have record warm Atlantic sea surface temperatures. So the forecast for this year even though it is above normal, like it was issued by NOAA a few months ago, there’s a lot of a lot of uncertainty because of the presence of the Pacific Niño, which is detrimental for hurricanes.

Bannin: Why hasn’t the Atlantic Nino got as much attention as regular Pacific El Niño? I know obviously, the Atlantic is a smaller basin than the Pacific, but still, it seems like a big predictor for major hurricanes.

Lopez: I think it goes back to the impacts of Atlantic Niño being smaller. Usually a large Atlantic Niño, for example, like the 2021, is considered to be an anomalous sea surface temperature, up to one degree above climatology, above the mean. Whereas, that is a very moderate Pacific Niño. So the communications between what goes on in the ocean and in the atmosphere, which leads to the remote effects of, say El Niño, are very different. And also, the impact of Pacific El Niño has more more global reach, if you will, than the impact of Atlantic Niño. It has been just very recently that more attention we have been placing in the in the Atlantic side of the story. But I think there’s a lot a lot more studies to be done with regard to the impacts of Atlantic Niño, not only locally for people, for example, that lives south of the Sahel region in Africa that depends a lot on monsoon rainfall, where Atlantic Niño is very central for them to get this monsoon of rainfall. But also now we’ve seen with this study, and others that Atlantic Niño has far reaching effects through for example, hurricane modulations.