An ozone hole over the Arctic could influence the formation or intensity of La Nina indirectly through its impact on atmospheric circulation and stratospheric dynamics, said Jim Roemer of weather forecasting firm Best Weather.
According to Mr. Roemer, there are now clearer signs that the US National Oceanic and Atmospheric Administration (NOAA) will officially announce the formation of La Nina in the next few weeks.
The combination of cooler waters moving west and a positive Southern Oscillation Index (SOI) are the main factors that will influence the weather over the next few months.
The positive SOI refers to low pressure around Darwin, Australia, and low pressure in the eastern Pacific near Tahiti. This is also a signal that La Nina is finally forming.
The US faced an "excessive" hurricane and tornado season in 2024, and the emerging La Nina is believed to be the main cause.
The term “excessive” may seem like a stretch, but it’s actually a meteorologically defined threshold. And while tornadoes and hurricanes are very different phenomena, they have one thing in common: the developing La Nina weather pattern has helped increase the frequency of tornadoes and hurricanes in 2024 — even if La Nina hasn’t played out exactly as scientists expected.
The 2024 Atlantic hurricane season produced 18 named storms. Five storms hit the lower 48 states: Beryl, Debby, Francine, Helene, and Milton. Three storms hit Florida.
For tornadoes, there were 1,762 preliminary reports of tornadoes from January to November. The average from 1991-2020 during this same time frame was 1,187 tornadoes nationwide.
La Nina is the opposite of El Nino, both phases of an alternating weather pattern that begins in the tropical Pacific Ocean. In the case of La Nina, cooler-than-average water temperatures prevail in the eastern Pacific Ocean. That coolness chills the air above, causing it to sink and push pressure higher, which in turn affects weather patterns in the atmosphere and causes downstream effects in North America and beyond.
There is a clear link between La Nina and hurricanes. Sinking air in the Pacific is countered by rising air in the Atlantic. That upward motion makes hurricanes more likely to form.
Forecasts for the 2025 hurricane season under the influence of La Nina show that hurricane activity in the Atlantic and Western Pacific often increases strongly.
In the Atlantic, under La Nina conditions, low pressure in the Atlantic and high pressure in the eastern Pacific create a favorable environment for hurricane formation. The 2025 hurricane season is expected to be another “super active” season with 18-20 named storms, including about 7-9 major hurricanes.
Meanwhile, storms in the Western Pacific region, including typhoons and depressions in the East Sea, are forecast to increase by about 15-20% compared to the average. This could cause Vietnam to face many strong and unusual storms in 2025.
