The National Oceanic and Atmospheric Administration’s Climate Prediction Center says there is a 60% chance that a weak A La Nina event will develop this fall and may last until March.
La Nina is part of a natural weather cycle that can cause extreme weather around the world – and its effects vary from place to place.
While there is no certainty as to how this La Nina will play out, there are some general trends. Experts say northern parts of South America could see above-normal rainfall. Southern US states and parts of Mexico may be drier than average. The northern part of the US and southern Canada will be wetter than average.
Experts say northern parts of South America could see above-normal rainfall. (AP Photo)
La Nina is the cooler phase of the El Nino-Southern Oscillation, a naturally occurring global weather pattern that involves changes in air and ocean temperatures in the Pacific and can cause extreme weather around the world.
El Nino is a warm phase and occurs when the trade winds that normally blow across the Pacific towards Asia weaken, allowing warm ocean water to accumulate on the western edge of South America. But during La Nina, the trade winds strengthen and cold water from the deep ocean rises, leading to cooler than average ocean temperatures in the eastern Pacific.
These cooler ocean temperatures and changes in the atmosphere affect the jet stream – a narrow band of fast-moving air that flows from west to east around the planet – by pushing it northward. The jet stream sits over the ocean and can absorb its moisture, influencing the direction of storms and increasing rainfall.
The southern US states and parts of Mexico may be drier than average. (AP Photo)
Earth recently had a “triple-dip” La Nina event from 2020 to 2023. ,” said Michelle L’Heureux, a climate scientist at NOAA. L’Heureux said La Nina’s tend to last longer and are more frequent than El Nino events.
“It’s unusual and unprecedented,” said Ben Cook, a climate scientist at the NASA Goddard Institute for Space Studies affiliated with Columbia University, about the La Nina forecast this year.
Cook noted that the frequency of La Nina events could depress regions that have experienced drought recently, such as East Africa. “If we go into another La Nina event, it means a continuation of those really bad conditions.”
La Nina weather effects
The influence La Nina has on the climate varies by location and season, L’Heureux said. Parts of South America, such as eastern Argentina, may be drier than average while Colombia, Venezuela and northern parts of Brazil may be wetter than normal.
“It depends on where you are. “Part of that is because there’s a monsoon cycle, a wet and dry season, that goes through Central and South America, so La Nina fundamentally changes the intensity and timing of those monsoon cycles,” L’Heureux explained.
In the US, the Northeast and Ohio Valley typically see wetter-than-normal conditions along the storm’s track because of the jet stream, said Samantha Borisoff, a climate scientist at NOAA’s Northeast Regional Climate Center based at Cornell University.
The cold jet stream can also cause cold outbreaks, especially in the central US Borisoff said snow is difficult to predict and depends a lot on the storm and the path it takes, but he noted that New England, New York and the Great Lakes region. it’s often snowier during La Nina winters, but that’s not a guarantee. The southern and southeastern US regions are far from the active storm track and tend to be drier and warmer than normal.
La Nina, El Nino and climate change
Scientists say the connection between climate change and La Nina and El Nino is not entirely clear.
Paul Roundy, a climate scientist at the University at Albany, said climate models tend to show regular El Ninos and unusual La Ninas, but not all models agree. Computer models also struggle to separate the regular variation in the El Nino and La Nina phases from a warming source of climate change in the oceans and atmosphere.
“I can’t imagine climate change not causing El Nino,” Roundy said. “That nature itself has so much power alone. So we could get more La Nina events, and maybe in 40 or 50 years we’ll be seeing the opposite.”