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A long-awaited La Niña has finally appeared, but the periodic cooling of Pacific Ocean waters is weak and unlikely to cause as many weather problems as usual, meteorologists said Thursday.

La Niña, the flip side of the better-known El Niño, is an irregular rising of unusually cold water in a key part of the central equatorial Pacific that changes weather patterns worldwide.

The last El Niño was declared finished last June, and National Oceanic and Atmospheric Administration forecasters have been expecting La Niña for months. Its delayed arrival may have been influenced—or masked—by the world's oceans being much warmer the last few years, said Michelle L'Heureux, head of NOAA's El Niño team.

"It's totally not clear why this La Niña is so late to form, and I have no doubt it's going to be a topic of a lot of research," L'Heureux said.

But even as the temperature signature was late to arrive and small at that, L'Heureux said some of the effects across the globe have shown up and forecasters have made seasonal predictions based on La Niña conditions.

In the United States, La Ninas tend to cause drier weather in the South and West. They tend to make weather wetter in parts of Indonesia, northern Australia and southern Africa, L'Heureux said. They typically bring more Atlantic hurricanes in summer months, but L'Heureux forecast that this La Niña will have dissipated by the summer.

El Niño often leads to rainier weather in the United States, and tends to increase temperatures globally while La Niña has the opposite effect. Studies have found that La Niña droughts have been costlier than weather extremes linked to El Niño.

The last La Niña ended in 2023 after an unusual three-year stretch.