A long-awaited La Nina 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 Nina, the flip side of the better-known El Nino, 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 Nino was declared finished last June, and National Oceanic and Atmospheric Administration forecasters have been expecting La Nina for months. Its delayed arrival may have been influenced by the world's oceans being much warmer the last few years, said Michelle L'Heureux, head of NOAA's El Nino team.

“It’s totally not clear why this La Nina 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.

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 Nina will have dissipated by the summer.

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

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

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