El Niño's waters are the hottest ever measured. They're getting hotter

Sea surface temperatures just hit a record high in a 2.4-million square mile region of the deep Pacific Ocean known as Niño 3.4, the key area scientists are tracking to measure the rapidly strengthening El Niño.

The daily average temperature – 85.73 degrees – on Sept. 29 was higher than at any other time on record in the region, according to preliminary data from the National Oceanic and Atmospheric Administration. It continued to climb the next day.

The temperature is about as warm as the ocean off Miami Beach and San Juan, Puerto Rico this week and warmer than the water off St. Petersburg, Florida, and Galveston, Texas.

“We are seeing a perfect storm of climate change and a super El Niño that is maturing so fast,” Ben Kirtman, dean of the University

of Miami Rosenstiel School of Marine, Atmospheric and Earth Science, told USA TODAY on Sept. 30. Sea surface temperatures in the region are still climbing and could continue into November, according to Kirtman.

NOAA emphasizes the Sept. 29 number is preliminary and could change when additional data from ships, buoys and other sources is integrated. However, water temperatures at buoys along a 1,000-mile swath of the 140th meridian on Sept. 30 ranged from 83.8 degrees to 87.8 degrees, according to data provided by NOAA's National Data Buoy Center.

The record-warm waters raise grave concerns for marine life and coral reefs and for the people and communities who make their living by the sea, said Bill Precht, a coral scientist and director of coastal and marine sciences for Florida-based Bio-Tech Consulting.

Why do sea surface temperatures matter?

Sea surface temperatures in the Niño 3.4 region are important because that’s where NOAA uses a three-month average to monitor the three phases and strength of the El Niño-Southern Oscillation, one of the planet’s most powerful climate patterns.

NOAA's Relative Oceanic Niño Index is the measure of how much warmer or cooler the central-to-eastern equatorial Pacific Ocean is relative to the rest of the global tropics, smoothed out across three months to reduce noise and spikes, said Brian McNoldy, a senior research associate at the Rosenstiel School.

Once the September sea surface temperature numbers are released in early October, the current El Niño will enter the “strong” category and is likely to be still climbing, McNoldy said. Strong is when the Relative Oceanic Niño Index reaches 2.7 to 3.6 degrees Fahrenheit, he said. An El Niño is “very strong” when the index reaches 3.6 degrees Fahrenheit or more.

What was the previous record? When was it set?

The previous all-time record daily temperature in the region was 85.68 degrees, set in November 2015, during one of the strongest El Niño events on record.

Kirtman and other scientists told USA TODAY in interviews over the summer that we're in "uncharted territory" with this El Niño and its impacts on top of climate change-induced warming. The El Niño developed earlier than expected, quickly strengthened and isn’t expected to peak until sometime later in 2026.

Experts watching evaporation

How much warmer could water temperatures reach in the area? "That’s an interesting question,” Michael McPhaden, a researcher at the University of Washington, told USA TODAY recently. He has studied El Niño for nearly 50 years.

Previously the thinking was the warmest average sea surface temperatures could reach was around 86 degrees (30 C), McPhaden said. "That’s because at that point, it’s likely that evaporation might begin to cool the water," he said. “The warmer it gets, the more you evaporate."

Now scientists aren't so sure. In a changing climate, he said the maximum possible temperature might increase over time.

The Niño region isn't alone in its record temperatures. The world daily sea surface average temperature has set daily records since June, setting a new all-time record in August, according to the Climate Reanalyzer with the University of Maine's Climate Change Institute. The Gulf of America, formerly known as the Gulf of Mexico, also has been setting daily records.

What impact could these warmer waters have?

Warmth in the El Niño region has pushed ocean temperatures higher in summer 2026, scientists have previously told USA TODAY, influencing a shift to a busier hurricane season in the Pacific and prompting migration of typically warmer water species into the waters off the California coast.

Doug McCauley, director of the Benioff Ocean Initiative at the University of California, Santa Barbara, said there have been reports of yellow sea snakes, hammerhead sharks and other species off the southern California coast. Reuters reported changing ocean conditions off South America reduced the food available to sea birds.

El Niño-related warming on top of the ocean heating from climate change, and the effects on coastal communities where marine life and corals are being disrupted by the changing conditions will be catastrophic, said Precht, the coral scientist.

Temperatures in locations around the world have been warmer in 2026 than anytime before, Precht said. "Now you superimpose the El Niño on local areas, like the Eastern Pacific, and it's catastrophic if you're a fisher working off of Ecuador, or the Galapagos or the Pacific side of Panama."

Coral bleaching heat stress alerts are at some of their highest levels from Mexico south along the Pacific coast, Precht said.

In the European Union's most recent Copernicus Ocean State Report, released Sept. 30, the United Nations Secretary General's Special Envoy for the ocean, Peter Thomson, said the report tells an unmistakable story: "The ocean is changing, and those changes are reaching into the lives, livelihoods and security of people everywhere."

Dinah Voyles Pulver, a national correspondent for USA TODAY, covers violent weather, climate and the environment, among other news. Reach Pulver at [e-mail] and Loehrke at [e-mail].

This article originally appeared on USA TODAY: El Niño's waters are the hottest ever measured. They're getting hotter