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Yahoo
03-05-2025
- Climate
- Yahoo
La Niña is dead — what that means for this year's hurricanes and weather
When you buy through links on our articles, Future and its syndication partners may earn a commission. After one of the strongest El Niños on record ended in 2024, meteorologists predicted La Niña — the counterpart to this climate pattern — would follow. Signals of a slowly developing and "unusual" La Niña strengthened over the winter, but began to falter in recent months. By March it was dead. So what happened — and how might that impact this summer's weather and the coming Atlantic hurricane season? El Niño is a seasonal shift in Pacific Ocean temperatures that can suppress hurricanes, change rainfall patterns and bend the jet stream. Its cold-water counterpart, La Niña, tends to do the opposite: feed Atlantic hurricanes and elevate wildfire risk in the West. Together, they form the El Niño-Southern Oscillation (ENSO). ENSO refers to seasonal climate shifts rooted in Pacific Ocean surface temperature changes. Changes in wind patterns and currents can draw cold water from the deep ocean, where it interacts with the atmosphere in complex ways. Even small deviations in sea surface temperatures can tilt global weather over the coming months toward hot and dry — or rainy and cool — depending on the region. "It's an incredibly powerful system," said Emily Becker, a University of Miami research professor and co-author of the National Oceanic and Atmospheric Administration's (NOAA) ENSO blog. "El Niño and La Niña conditions affect rainfall, snow, temperature, the hurricane season, and tornado formation. They've been tied to fluctuations in the financial markets, crop yields, and all kinds of things.' "Scientifically, we care about it because it's really cool," she told Live Science. "But practically, we care because it gives us this early idea about the next six to 12 months." Scientists monitor a narrow strip in the Pacific Ocean near the equator. A 0.9-degree-Fahrenheit (0.5-degree Celsius) rise or fall in average surface temperature there, sustained for five overlapping three-month periods, can signal the onset of El Niño or La Niña, respectively. However, the "average" is a moving target, based on a 30-year baseline, from 1991 to 2020, which is becoming outdated as the climate warms. "We're always playing catch-up," Tom Di Liberto, a former NOAA meteorologist and ENSO blog contributor, told Live Science. ENSO-neutral patterns occur when surface temperatures hover near the long-term norm. But neutral doesn't mean benign — it may just mean the forecast is trickier. Instead of asking why La Niña was short-lived, the better question might be whether it happened at all. While ocean surface temperatures this winter dipped below average, they didn't stay that way long enough: By mid-April, NOAA forecasters revealed that a full-fledged La Niña event had failed to develop. Why not? "Trade winds play a big role," Muhammad Azhar Ehsan, a climate scientist at Columbia Climate School's Center for Climate Systems Research, told Live Science. He explained that weakening trade winds in the eastern Pacific likely kept cold water from rising to the surface — a key step in forming a robust La Niña. But the story may not be over. When the 30-year temperature baseline is revised to include more recent, warmer years, future analysts might reclassify this winter's La Niña in the historical record, even if it didn't qualify in real time. Without El Niño or La Niña tipping the scale, forecasting gets harder. These patterns sharpen the blur of seasonal predictions, adding crucial information about how the weather might drift from the usual script. Without them, when ENSO is neutral, they're left squinting into the future with little more than historical averages and climate trends. "Without an El Niño or a La Niña, a range of other factors drive seasonal weather," James Done, a project scientist at the NSF National Center for Atmospheric Research, told Live Science. "These are less well understood, and the strength of the relationships is weaker. It's very complex." Still, forecasters generally agree that this summer will likely be hotter than normal. "Surprise, surprise," Done said, "we have a background warming trend." El Niño usually suppresses hurricanes, whereas La Niña and neutral conditions let them run wild. With a warm Atlantic and ENSO expected to stay neutral, that could mean a busy season. "El Niño tends to increase vertical wind shear, and vertical wind shear tears apart hurricanes," Phil Klotzbach, a research scientist and hurricane forecast expert at Colorado State University, told Live Science via email. "Consequently, [without El Niño], we anticipate relatively hurricane-favorable wind shear patterns this summer and fall." Others offered optimism. Ehsan said a cooling trend in the Atlantic from February to March could signal a quieter Atlantic hurricane season. However, scientists say old rules of thumb become less reliable as background conditions change. "Last year was a weird one," Di Liberto said, referring to La Niña. "All signs pointed toward a horrible hurricane season, but it wasn't the worst-case scenario it could have been." 2023 didn't follow the script either. "We had an El Niño in 2023 but still saw more storms than usual," Done said. "So, there's a big debate: Does El Niño still kill off hurricanes, or are oceans now so warm that it changes the relationship? It's an open question." In an April 10 statement, NOAA representatives wrote that El Niño or La Niña conditions likely won't turn up this summer and that ENSO-neutral conditions are expected to last through October. As summer fades to fall and winter, the chances for La Niña rise, but the most likely scenario is still ENSO-neutral. That said, scientists caution against putting too much stock into springtime ENSO forecasts. "Spring is a messy time for forecasting," Di Liberto said. That's because ENSO conditions primarily form during winter and fade into the spring, offering fewer reliable signals. "June is usually when things get more confident," he added. No one knows how climate change will affect ENSO patterns, but scientists are concerned about the warming oceans and atmosphere. "Warmer air holds more water. It's fundamental," Becker said. "That's a factor in why we're seeing some hurricanes deposit unbelievable amounts of rain — it's partly due to the higher moisture capacity of the atmosphere." RELATED STORIES —How strong can hurricanes get? —Here's why storm surge during hurricanes can be so catastrophic —Birth of a hurricane: What meteorologists look for as they hunt for early signs of a tropical cyclone forming Warm waters can extend a hurricane season or fuel storms farther north. Once envisioned as coastal threats, storms are increasingly driving inland. For example, Hurricane Helene devastated Appalachian communities hundreds of miles from the sea in 2024. "You're making a better and bigger sponge, and it gets wrung out somewhere," Di Liberto said. "And communities have to deal with incomprehensible amounts of rainfall and flooding." However, our understanding of hurricanes is incomplete, Done said. Our observational record extends back less than 160 years — just a blink of geologic time. Scientists who have studied the geologic record of ancient cyclones have found evidence of stronger hurricanes making landfall in the distant past, often tied to periods of climate change. If the present is the key to the past, the past nods back: Earth has seen worse — and with oceans warming fast, scientists warn it may only be a matter of time before historically unprecedented storms strike again.
Washington Post
10-04-2025
- Science
- Washington Post
La Niña is over. Scientists now say it was stronger than it seemed.
La Niña is over, scientists declared Thursday. And while the climate pattern was notably brief and had been waning, scientists said the episode was not as weak as it once seemed. When the planet-cooling climate pattern emerged this year, scientists said it developed later and in a weaker state than they had expected. But researchers say that is because unusual warmth that has dominated the Pacific and other global oceans for the past two years masked La Niña, which is defined by a patch of cooler-than-normal Pacific waters. La Niña's end, which the National Oceanic and Atmospheric Administration announced Thursday, marks the beginning of an uncertain spell in global weather, with no strong driver of seasonal patterns and trends in temperature or precipitation. Forecasters instead will have to look toward factors that influence the climate on a weekly to monthly scale that can be harder to predict, even as some of even as some of La Niña's characteristics, such as a drying influence in the Southwest United States, may increase the likelihood of an active fire season. But forecasters said the pattern that follows this one will drive more uncertainty than usual. The traditional measure of La Niña and its better-known inverse, El Niño, looks at differences in temperature across specific zones of the Pacific. And based on that metric, the La Niña episode that officially began this winter was weak and expected to have relatively minor impacts on global weather. But the surge in baseline ocean temperatures tied to global warming made La Niña's signature zone of cool Pacific waters look warmer than they otherwise would have been. Cooler waters mean a stronger La Niña. When accounting for that warming, the La Niña was closer to moderate strength, scientists said, fueling dry conditions across the southern United States that have set the stage for a potentially active fire season for the Southwest. Scientists have been tracking the difference between the typical way La Niña and El Niño are diagnosed, and a new standard that takes the trend of global warming into account. 'It's one of the first times we've seen such a large difference,' said Emily Becker, associate director of the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami. The index that takes into account nearly 1.5 degrees Celsius (2.7 degrees Fahrenheit) of global warming more accurately captured the weather impacts La Niña caused in the United States, she said. Had scientists at NOAA and other climate agencies used the new index to track La Niña's development, they also likely would have declared its arrival earlier and more accurately, said Pedro DiNezio, an associate professor at the University of Colorado at Boulder. But it's not clear that the new measure is better. Scientists are investigating whether they should replace the traditional metrics applied to what is known as the El Niño-Southern Oscillation, or ENSO, with the new global warming-adjusted index. Just because the new index worked better this time doesn't mean it always will, Becker said. 'We're going to need to compare the two across many different situations, with many different global background conditions before we can make a call like that,' Nathaniel Johnson, a climate scientist at NOAA's Geophysical Fluid Dynamics Laboratory, wrote on the agency's ENSO Blog. It was just three months ago that NOAA declared La Niña had arrived, with requisite signs of the cooler-than-normal waters along the equatorial Pacific and wind patterns that push warmer waters and towering clouds to the west, toward Indonesia. Typical La Niña events can last anywhere from nine months to two years. The planet's most recent La Niña lasted, unusually, for three years. But now, the planet is entering what are known as 'ENSO neutral' conditions, without the influence of La Niña or El Niño to suggest what sort of temperature or precipitation patterns that parts of the world can expect. That also means the outlooks for wildfire season in the West and hurricane season in the East will depend on monthly and weekly variations in weather patterns that cannot be as reliably predicted so far in advance. While La Niña's drying influence has raised the likelihood of an active fire season, recent early predictions of a busy but not hyperactive Atlantic hurricane season carry more uncertainty than usual, forecasters said. Forecast model updates for April have started to arrive, and the consensus is that neutral conditions will continue across the tropical Pacific Ocean into summer. However, from late summer into fall, forecasts start to diverge. Some model outlooks suggest that the Pacific will warm up, while others suggest that a dip back toward La Niña could occur — this uncertainty is at least partially tied to the 'spring predictability barrier,' the time of year when long-range forecasts for El Niño and La Niña have lower skill. If the ocean begins to lean even slightly toward El Niño or La Niña later this year, it can have an influence on hurricane season. La Niña-like patterns tend to cause winds that are more conducive to hurricanes in the Atlantic. For now, NOAA scientists estimate about a 43 chance of neutral conditions by late fall, with a 38 percent chance of La Niña and less than 20 percent chance of El Niño. But those odds are likely to shift over the coming months, as the climate patterns are difficult to predict at this time of year, during Northern Hemisphere spring, when the climate is naturally in flux. 'After the spring, I think we'll see a clearer picture,' Becker said.
