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Expand chart
Data: NOAA; Map: Harry Stevens/Axios

El Niño, the climate cycle in the tropical Pacific Ocean that can reconfigure weather patterns, is slowly but steadily building for 2019 — but there is a component of it that is still missing in action.

Why it matters: El Niño events are one of the most consequential forces that can tip the odds in favor of particular weather patterns. But they require both unusually warm ocean temperatures in the tropical Pacific and changes in the atmosphere — and so far, the atmosphere hasn't changed.

The big picture: El Niño events can make or break a ski season in the Western U.S. by directing storms across the southern tier of the country, and they tend to favor milder-than-average conditions in the Midwest and Pacific Northwest. They can also boost global average temperatures, adding to the influence of human-caused global warming, which acts on far longer timescales.

During the past two decades, scientists have become adept at forecasting the onset and intensity of El Niño events. A telltale sign of El Niño's arrival is a sharp increase in equatorial tropical Pacific Ocean temperatures.

  • Part of its definition is now being met, as sea surface temperatures in part of the Pacific have reached 1°C, or 1.8°F, above average for this time of year.

Between the lines: Yet, the ocean temperatures are only part of the equation, as indicated by forecasters' reluctance to announce El Niño's arrival. Instead, to get an El Niño requires a series of interactions between the ocean and the atmosphere. This is why meteorologists refer to El Niño as a "coupled system."

  • Right now, the ocean is asking the atmosphere to play along, and the air is pretending not to hear anything. That is expected to change soon, however.

"While warmer-than-average surface waters in the equatorial Pacific are an essential element of El Niño, the atmospheric response is just as critical," says Mike Halpert, deputy director of NOAA's Climate Prediction Center, via email.

Signs that experts like Halpert are looking for before declaring an El Niño advisory include:

  • A slackening of the easterly trade winds along and north of the equator.
  • Increased rainfall near the International Dateline.
  • Clear and persistent sea level pressure changes across the world's largest ocean.

The bottom line: Halpert says that temporarily, the Pacific appears to be dominated by other tropical weather cycles. But he and other forecasters expect the ocean to eventually win over the weather patterns, with at least a 90% chance that El Niño will develop this winter.

Go deeper

Updated 7 hours ago - World

Mexican President López Obrador tests positive for coronavirus

Mexico's President Andrés Manuel López Obrador during a press conference at National Palace in Mexico City, Mexico, on Wednesday. Photo: Ismael Rosas/Eyepix Group/Barcroft Media via Getty Images

Mexican President Andrés Manuel López Obrador announced Sunday evening that he's tested positive for COVID-19.

Driving the news: López Obrador tweeted that he has mild symptoms and is receiving medical treatment. "As always, I am optimistic," he added. "We will all move forward."

7 hours ago - Politics & Policy

Sarah Huckabee Sanders to run for governor of Arkansas

Sarah Huckabee Sanders at FOX News' studios in New York City in 2019. Photo: Steven Ferdman/Getty Images

Former White House press secretary Sarah Huckabee Sanders will announce Monday that she's running for governor of Arkansas.

The big picture: Sanders was touted as a contender after it was announced she was leaving the Trump administration in June 2019. Then-President Trump tweeted he hoped she would run for governor, adding "she would be fantastic." Sanders is "seen as leader in the polls" in the Republican state, notes the Washington Post's Josh Dawsey, who first reported the news.

Coronavirus has inflamed global inequality

Illustration: Aïda Amer/Axios

History will likely remember the pandemic as the "first time since records began that inequality rose in virtually every country on earth at the same time." That's the verdict from Oxfam's inequality report covering the year 2020 — a terrible year that hit the poorest, hardest across the planet.

Why it matters: The world's poorest were already in a race against time, facing down an existential risk in the form of global climate change. The coronavirus pandemic could set global poverty reduction back as much as a full decade, according to the World Bank.