Hurricane season is weeks away. Cooling in the Pacific could drive more activity.

A sharp cooling trend has occurred in an ocean region that has important consequences for what happens in the upcoming hurricane season.

The patch of water, west of Peru and Ecuador in South America — about 3,000 miles south of Washington — unexpectedly warmed several degrees above average earlier in the year. Because of that warming, it looked unlikely that another hurricane-season enhancing La Niña would develop this year.

But the pattern has now reversed course, just weeks before the season’s start.

Soon after La Niña was declared over by the National Oceanic and Atmospheric Administration, strong winds churned up cool waters from below — a process called upwelling. And it happened unexpectedly fast. If the trend continues, it could encourage the return of La Niña-like conditions in the Pacific Ocean later this year. And if that happens, winds over the Atlantic Ocean may become more conducive to hurricane formation during the season that runs from June to November.

But it remains uncertain how much of an impact this cooling could have, since the Atlantic Ocean has also experienced a significant temperature dip. Waters in the Main Development Region for hurricanes are significantly cooler than this time last year, meaning there’s less fuel available for storms.

It’s possible the factors will balance each other out to some extent, resulting in an average season. It’s also possible that either element could win out, exerting more influence over hurricane season than the other. The likelihood of these outcomes will become clearer in the months ahead. Early outlooks suggest hurricane season is unlikely to be as active as last year, but could feature average to slightly above-average amounts of tropical systems.

What to know about the Pacific

With hurricane season now just weeks away, forecasters are closely monitoring the fluctuating temperatures in the Pacific Ocean — not just for what it means for hurricane season, but for how warm conditions may be in the Northern Hemisphere as summer approaches.

Despite being far from where hurricanes form in the Atlantic, the tropical Pacific Ocean has a powerful influence on weather patterns there — and around the globe.

This influence is part of a phenomenon known as an atmospheric teleconnection. Think of it like a long-distance phone call between different parts of the atmosphere: sometimes the signal is fuzzy, full of static and hard to interpret. Other times, the connection is crystal clear and direct.

Meteorologist Andy Hazelton said he thinks the erosion of the warmth in the eastern Pacific will make it less likely that an El Niño would emerge and have any influence on this year’s hurricane season.

“It looks like we’ll mostly likely stay neutral, which tends to be similar to La Niña with lower wind shear across the Atlantic,” Hazelton said.

Wind shear refers to the change of winds with height, which, when strong, can prevent tropical systems from forming. Wind shear in the Atlantic tends to be reduced during La Niña and neutral episodes.

Changes in the Pacific have global implications, too.

Although La Niña events are known for their planetary cooling effect, the latest one did little to quell the planet’s warming trend, since 2025 had the second-warmest start to a year (January to March) on record.

With El Niño unlikely in 2025, it could prevent another record warm year globally, but not by much.

Cooling in the Atlantic

Another ocean region that scientists monitor is called the Main Development Region — a stretch of seas from west of Africa to the Caribbean where most hurricanes form.

Warmer ocean temperatures in this region are linked to more storms, which is one reason forecasters were so concerned about the potential for a hyperactive hurricane season last year.

This important region is much cooler than the same time last year, by nearly 2 degrees, the largest decrease from one April to another on record.

Hazelton added that while there’s still time for this region to turn warmer, he sees it as the main factor that would prevent this hurricane season from being as active as the last one.

How oceans are monitored

While weather terms such as La Niña and El Niño are more recognizable terms these days, that wasn’t always the case.

In late 1982 and early 1983, one of the strongest El Niño events of the 20th century unfolded, featuring extremely warm ocean water in the eastern Pacific — but its wide-reaching and destructive impacts came with hardly any warning and caught scientists by surprise.

Motivated by the lack of early warning, there was a push to better monitor, predict and understand changes in the tropical Pacific Ocean, home to the El Niño and La Niña phenomena.

A deep ocean mooring system would later be developed by the Pacific Marine Environmental Laboratory with support from NOAA.

The system was designed to measure surface and subsurface ocean conditions in dozens of locations across the Pacific, with its data transmitted back to shore by satellites.

Now, about 40 years later, more than 4,000 autonomous floats collect sea temperature and salinity data worldwide, helping provide early alerts about El Niño and La Niña, as well as ice volume and sea level.

This observational data is supplemented by ship reports and satellites that use infrared sensors to detect thermal radiation and measure the temperature of the sea surface.

Over time, these developments made it possible to detect the kinds of deviations in the sea that scientists are now observing. And it’s why we know sea temperatures are cooling in a desolate part of the eastern Pacific Ocean, 3,000 miles from Washington.