USA TODAY US Edition

La Niña could worsen hurricane season, forecaster­s say

- Doyle Rice Contributi­ng: Dinah Voyles Pulver

La Niña is still on track to form this year, government forecaster­s announced Thursday morning, giving the climate pattern a 62% chance of developing during the upcoming summer months (June-August). Among other impacts, the emergence of La Niña could help boost the severity of the Atlantic hurricane season.

Forecaster­s also reported that the recent strong El Niño remains in effect, but is weakening and expected to transition to “ENSO-neutral” conditions over the next few months. The entire El Niño/La Niña cycle is known as the El Niño Southern Oscillatio­n (ENSO), and its three phases (El Niño, La Niña, and ENSO-neutral), can affect weather in the U.S. and around the world.

What is La Niña?

La Niña is a natural climate pattern marked by cooler-than-average seawater in the central and eastern Pacific Ocean.

It is one of the main drivers of weather in the United States, especially during the late fall, winter and early spring. It’s the opposite to the more well-known El Niño, which occurs when Pacific Ocean water is warmer than average.

Signs of La Niña are starting to be seen in the Pacific: “We’re starting to see hints of cooling at the surface in a small region of the eastern Pacific,” said physical scientist Michelle L’Heureux with the Climate Prediction Center.

Additional­ly, “there is a historical tendency for La Niña to follow strong El Niño events,” according to the announceme­nt from the Climate Prediction Center.

Can La Niña worsen the Atlantic hurricane season?

Yes, according to the Climate Prediction Center, La Niña can contribute to an increase in Atlantic hurricane activity by weakening the wind shear over the Caribbean Sea and tropical Atlantic Basin, which enables storms to develop and intensify.

Vertical wind shear refers to the change in wind speed and direction between roughly 5,000-35,000 feet above the ground, NOAA said. Strong vertical wind shear can rip a developing hurricane apart, or even prevent it from forming. This is what can happen in the Atlantic during an El Niño when Atlantic hurricane activity is often suppressed.

While La Niña tends to increase hurricanes in the Atlantic, it also tends to decrease their numbers in the eastern and central Pacific Ocean basins.

What does La Niña mean for weather in the US?

La Niña (along with El Niño and ENSO-neutral) typically have minimal impact on U.S. weather in the summer, other than their effect on hurricanes. Winter is the one season in which they have the most impact.

“When we’re in ENSO-neutral, other climate drivers, like the Madden-Julian Oscillatio­n, become more noticeable,” National Weather Service meteorolog­ist Erica Grow Cei told USA TODAY. Overall, she said forecaster­s at the Climate Prediction Center place odds on a milderand drier-than-average spring across most of the country.

As for La Niña winter impacts, a typical La Niña winter in the U.S. brings cold and snow to the Northwest and unusually dry conditions to most of the nation’s southern tier, according to the Climate Prediction Center. The Southeast and mid-Atlantic also tend to see warmer-than-average temperatur­es during a La Niña winter.

Meanwhile, New England and the Upper Midwest into New York tend to see colder-than-average temperatur­es, the Weather Channel said.

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