Hurricane season forecast is already looking grim: Here's why hot oceans, La Niña matter

Hurricane Idalia approaches the western coast of Florida while Hurricane Franklin churns in the Atlantic Ocean at 5:01 p.m. EDT on August 29, 2023.

With three months to go until Atlantic hurricane season starts, the chances for a La Niña by summer are increasing, and that’s an anxiety-inducing forecast for those still recovering from hurricanes along the Gulf of Mexico and Atlantic seaboard in recent years.

“We’ve got possibly extremely warm sea surface temperatures, especially in the main (hurricane) development region and the prospect of La Niña being in place,” said Florida State climatologist David Zierden. “That’s not good news for hurricane season.”

La Niña, a pattern of cooler waters along the equator in the Pacific Ocean, often leads to more active hurricane seasons. It tends to reduce vertical wind shear over the Atlantic and allow budding tropical storms to build the high cloud structures that can supercharge their energy.

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Meanwhile, sea surface temperatures in the tropical Atlantic are already running above normal, even warmer than last year. Ocean surface temperatures globally set another new record high, reaching 21.13 degrees Celsius last Wednesday, or just over 70 degrees Fahrenheit, according to the most recent data available through the University of Maine’s Climate Reanalyzer. That’s a slight increase above the 21.1 degree-record set last April and again last August.

What’s the forecast for La Niña?

The signs are showing a shift from the strong El Niño that has been in place in the Pacific over the past year, said Jason Dunion, a meteorologist at the University of Miami and the National Oceanic and Atmospheric Administration’s Hurricane Research Division.

The bright bands of dark orange on sea surface temperature maps that show El Niño’s warmer-than-normal waters along the equator are fading rapidly.

The entire El Niño/La Niña cycle is known as the El Niño Southern Oscillation, and its three phases can affect weather around the world. Whether the oscillation shifts to neutral this summer or to a La Niña remains to be seen.

The latest forecast puts the chances for a La Niña arriving by the heart of hurricane season at 75% or greater, Zierden said. As a result, he expects the seasonal forecasts from Colorado State University and NOAA to call for a very active season.

But the oscillation is far from the only key ingredient in cooking up hurricanes. Warm waters are essential.

How do hurricanes form? An inside look at the birth and power of ferocious storms

Warm water – nature’s hurricane fuel

Warm water “can provide more fuel for storms, potentially leading to a higher number of storms and possibly greater intensity,” said Hui Li, a project scientist at the University Corporate for Atmospheric Research.

Seasonal forecasters are very closely monitoring the Eastern Atlantic, where sea surface temperatures in the region off the African coast are 1, 2 and even 3 degrees Celsius warmer than normal right now, Dunion said. “And it’s not even spring yet.”

More than half the tropical systems each year come from that “hurricane nursery,” and 80% to 85% of the major hurricanes, Dunion said. So it’s “a really important place.”

With warm temperatures to the east and less wind shear to the west, Dunion said, storms could get a boost from both sides as they advance across the Atlantic Ocean.

Other factors that can influence hurricane season don’t develop until later in the summer, Zierden said, such as rainfall and dust storms off western Africa.

It’s “still early for making seasonal outlooks, and numerous uncertainties exist,” Li said. “The timing of the La Niña transition will likely play a crucial role.”

It takes the right ingredients for tropical systems to form, including warm sea surface temperatures, a moist environment and low wind shear, Zierden said. To get a Category 4 or 5 hurricane, it takes perfect conditions, and those don’t always line up.”

Besides that, he said, knowing the projected number of hurricanes doesn’t tell anyone which regions are mostly to be affected by a hurricane.

What happened during the 2023 hurricane season?

The season wound up ranking fourth for the most named tropical storms since 1950, the National Hurricane Center said. The overall number of hurricanes and major hurricanes was about average, with seven hurricanes and three major hurricanes.

Only one hurricane – Idalia – made landfall on the U.S. mainland last year. It left a trail of devastation across North Florida after a rare landfall just south of the state’s Big Bend region, even flinging small flocks of flamingos across the eastern U.S.

Typically, the strongest influence of El Niño tends to be in the western Caribbean and the Gulf of Mexico, where the winds increase that shear off the high cloud structures of hurricanes, Dunion said. But last year, sea surface temperatures in the eastern Atlantic were much warmer than normal.

Could the season have had even more hurricanes without El Niño? Did the warm sea surface temperatures muscle out El Niño?

A number of scientists are interested in the competing factors, Dunion said. “There are still a lot of studies going on, and a lot of speculation.”

What to remember about hurricane season

Things like El Niño and La Niña are useful in the big picture, said Alan Sealls, a retired television meteorologist and adjunct professor at the University of South Alabama. “But the problem is we all live in the little picture, and they just don’t tell us what could happen or where it would happen exactly where we live.”

Despite the rising odds, it’s worth remembering that everything actually comes down to what the atmosphere will be doing during any given week of hurricane season, Sealls said. Even if the odds continue to increase, he said, it won’t give “any advance notice for where things get crazy, if they get crazy.”

The threat of an active hurricane season doesn’t prompt Louisiana officials to preach an “extra layer” of preparedness, said Mike Steele, director of communications for the Governor’s Office of Homeland Security and Emergency Preparedness. Louisiana residents suffered four hurricanes that made landfall from August 2020 to August 2021, including three hurricanes.

The state wants its citizens to remain prepared year round, regardless of the forecast, Steele said. “You can’t hang your hat on hope, you hang your hat on being prepared.”

This article originally appeared on USA TODAY: Hurricane season forecast is already looking grim: Here’s why hot oceans, La Niña matter