NOAA's Climate Prediction Center says El Niño is still strengthening in the tropical Pacific, and its forecasters give a 75 percent chance that the October through December period will produce a historic event, stronger than any El Niño on record since 1950. The latest weekly ENSO update from the Climate Prediction Center, dated September 21, keeps an El Niño Advisory in place and repeats a greater than 90 percent chance of a very strong event during the Northern Hemisphere fall and winter of 2026-27.

The pattern is lining up with weather that is already making news. Tropical Storm Nolo is threatening Hawaii's Big Island, Hurricane Polo became one of the fastest-intensifying storms on record in the eastern Pacific, and the Atlantic has gone later into September without a hurricane than any season since 1914.

For households on the U.S. mainland, the bigger question is what comes next. El Niño's strongest influence on the continental United States typically arrives in winter, and NOAA's seasonal outlooks already lean toward a wetter southern tier and a warmer northern tier.

The Numbers Behind "Very Strong" and "Historic"

El Niño is tracked by how much warmer than normal the ocean surface is in a stretch of the central and eastern equatorial Pacific called the Niño-3.4 region. NOAA considers an event "very strong" when those temperatures exceed normal by more than 2.0 degrees Celsius (3.6 degrees Fahrenheit), a level often called a super El Niño.

NOAA defines "historic" more precisely. In its monthly diagnostic discussion, the Climate Prediction Center said a historic event would mean a three-month value of +2.5°C (4.5°F) or more on its Relative Oceanic Niño Index, a measure that subtracts average warming across the whole tropical ocean. That would exceed every El Niño since 1950, including the major events of 1997-98 and 2015-16.

The most recent three-month value on that index, for June through August, was +1.4°C. In the latest weekly data, the Niño-3.4 region ran 2.1°C above normal, while regions farther east ran warmer still: +3.0°C in the Niño-3 region and +3.9°C in the Niño-1+2 region near South America.

NOAA's forecast is a probability, not a guarantee. The agency noted that with an event this large, "the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed." The next monthly discussion is scheduled for October 8.

Pacific Storms and a Silent Atlantic

During El Niño, unusually warm water in the central and eastern Pacific fuels thunderstorms and shifts wind patterns. NOAA has noted that El Niño tends to limit tropical activity in the Atlantic while it can enhance storm development in the Pacific, and this season fits that pattern.

As of 5 p.m. HST on September 23, a Hurricane Watch for Hawaii County was in effect as Tropical Storm Nolo approached from the south. Forecasters expected Nolo to become a hurricane by Thursday night and possibly a major hurricane by the weekend, with 15 to 20 inches of rain across the Big Island. According to The Weather Company's forecast for Tropical Storm Nolo in Hawaii, Nolo is the state's fourth tropical system of the season, and parts of the Big Island are still recovering from flooding caused by Hurricane Lala in August.

Farther east, Hurricane Polo intensified from a tropical storm to Category 5 strength in about a day off southwestern Mexico, a pace the National Hurricane Center called "truly remarkable," CNN reported. CNN noted that Polo's intensification was among the fastest on record in the eastern Pacific, where Hurricane Patricia set the 24-hour record in 2015. Polo's winds peaked at 180 mph.

The Atlantic shows the flip side. El Niño strengthens upper-level winds over the tropical Atlantic, creating wind shear that tears apart developing storms. As of late September 23, the basin had produced six named storms and no hurricanes.

No single storm can be pinned on El Niño alone. Water temperature, steering winds, and local conditions all matter, and measuring El Niño's role in any one event would require a formal attribution study.

A Wetter South and Milder North This Winter

El Niño's effect on U.S. weather peaks in winter. In NOAA's announcement when El Niño formed in June, the agency said the jet stream over the North Pacific tends to shift south during El Niño winters, steering storms across the southern tier while leaving the Northern Rockies and the Ohio and Tennessee valleys drier. El Niño also often brings a warmer-than-usual winter to the northern United States.

The Climate Prediction Center's winter outlook, updated September 17, favors above-normal precipitation across much of the southern tier, from California and the Southwest through the Gulf Coast and much of the East Coast, and above-normal temperatures across much of the country, with the strongest warm signal in parts of the northern tier. That points to better odds of a stormier, wetter winter for cities such as Los Angeles, Phoenix, Houston, New Orleans, Atlanta, and Tampa, and a milder one across much of the North.

These are odds, not a schedule. Cold air outbreaks can still reach the North in an El Niño winter, and a wetter storm track brings snow or ice to the South only when cold air arrives at the same time.

Preparing Homes for an El Niño Winter

The practical risks differ by region. In Southern California, heavy rain on steep hillsides and recent burn scars can trigger flash floods and debris flows, so residents near steep terrain should know their county's evacuation alerts. Along the Gulf Coast and in Florida, repeated winter storms can bring flooding, making drainage checks and a review of flood insurance worthwhile. Standard homeowners policies generally do not cover flood damage.

In the northern tier, a milder winter may lower heating demand for some households, though a warm outlook does not rule out short, sharp cold snaps. Water managers across the Southwest are watching whether a wet winter eases drought, while some northern ski areas could see a weaker snow season.

Hawaii residents should follow Hawaii County Civil Defense and the National Weather Service in Honolulu for Nolo, and prepare now if they live in flood-prone areas or on steep slopes.

Beyond This Winter

Because global average temperatures typically peak several months after the Pacific warming does, scientists expect a strong El Niño to push global temperatures higher into next year.

The Climate Prediction Center will publish its next ENSO diagnostic discussion on October 8 and updated seasonal outlooks later in October. For now, the most useful steps are to check local National Weather Service forecasts, review insurance coverage before the rainy season, and treat seasonal outlooks as a guide to risk rather than a promise of specific weather.

What Readers Want to Know

How strong is the current El Niño?

NOAA gives a greater than 90 percent chance of a very strong event this fall and winter and a 75 percent chance that October through December produces a historic event, the strongest since 1950.

What does "historic" mean in NOAA's forecast?

NOAA defines a historic event as a three-month value of +2.5°C or more on its Relative Oceanic Niño Index, which would exceed every El Niño since 1950.

Did El Niño cause Tropical Storm Nolo or Hurricane Polo?

El Niño favors tropical activity in the central and eastern Pacific, but no single storm can be blamed on it without a formal attribution study.

Why has the Atlantic been so quiet?

El Niño strengthens upper-level winds over the Atlantic, creating wind shear that prevents storms from organizing. The basin had no hurricanes as of late September 23.

What will El Niño mean for U.S. winter weather?

NOAA's outlook favors a wetter southern tier and above-normal temperatures across much of the country, especially the North. These are probabilities, not guarantees.

When is the next NOAA El Niño update?

The Climate Prediction Center's next ENSO diagnostic discussion is scheduled for October 8, with updated seasonal outlooks later in October.