La Nina's role explained in Atlantic hurricane season

UPI

2 days ago

1 of 3 | Large parts of New Orleans were flooded weeks after several levees failed in the wake of Hurricane Katrina in September 2005. That hurricane occurred around the onset of La Niña conditions. File Photo by Bob McMillan/FEMA Photo for UPI | License Photo
Most people associate La Niña with warmer winters or drought in the southern United States, but its influence stretches far beyond the winter months. When La Niña sets in during hurricane season, it has the potential to dramatically increase both the number and strength of tropical storms and hurricanes in the Atlantic basin.
La Niña is part of the El Niño-Southern Oscillation (ENSO) cycle and is defined by lower-than-average sea-surface temperatures in the eastern Pacific Ocean near the equator. Although the phenomenon originates far from the Atlantic Ocean, it disrupts global weather patterns in a way that suppresses wind shear across much of the tropical Atlantic.
This matters because vertical wind shear -- the change in wind speed or direction with height - tends to prevent tropical systems from organizing. When shear is reduced, clusters of showers and thunderstorms are more likely to organize, strengthen and turn into tropical storms and hurricanes.
"La Niña increases the number of hurricanes that develop and allows stronger hurricanes to form," said AccuWeather Lead Hurricane Expert Alex DaSilva. "It also raises the chances for the continental U.S. and the Caribbean Islands to experience a hurricane."
During La Niña years, meteorologists often observe more named storms, more major hurricanes and higher accumulated cyclone energy (ACE), a measure of the strength and duration of storms over time. The odds of U.S. landfalls also increase, particularly for the Gulf Coast and Southeast.
Two of the most active hurricane seasons in modern history occurred around the onset of La Niña conditions: 2005 and 2020. In 2005, Hurricane Katrina devastated the Gulf Coast, and the official storm naming list was exhausted for the first time, prompting the use of Greek letters.
In 2020, the Atlantic basin experienced a record-breaking 11 storms that made direct landfall on U.S. soil, including Hurricane Laura.
As for 2025, La Niña is not expected during the early part of the hurricane season. However, forecasters are watching for signs that it could emerge later in the year.
"If we trend toward La Niña late in the hurricane season, we could see an active end to the season, similar to what we saw last year," DaSilva said.
Complicating matters is the presence of unusually warm water in the Atlantic Ocean, which increases the risk of rapid intensification -- a dangerous trend in which storms gain strength quickly just before landfall.
One of the biggest factors for tropical development in 2025 is the abundance of warm water available to fuel storms.
"The water temperatures across most of the Atlantic are above average for this time of the year," DaSilva said. "They're not quite as warm as what we saw last year and in 2023, but they're still well, well above average."
If La Niña arrives in the second half of the season and combines with this ocean heat, the Atlantic could be primed for a particularly volatile stretch during the peak hurricane months of September through November.
La Niña doesn't guarantee an above-average season, but it dramatically shifts the odds in that direction. And for coastal communities, that makes understanding its influence more important than ever.