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Helene is almost a hurricane. See how path intensified

Vaseline September 24, 2024

The forecast for Helene to develop from a potential tropical cyclone into a Category 3 hurricane appears to be the fastest development the National Hurricane Center has ever predicted for a depression.

“They’ve never forecast a major hurricane within 60 hours for a disturbance below tropical storm level,” said Sam Lillo, a meteorologist and software engineer for DTN Weather, based on a computer analysis of the center’s historical forecast data. “The whole forecast is also basically faster than we’ve ever seen for 36 hours and 48 hours of a tropical depression.”

The National Hurricane Center didn’t have those statistics available Tuesday because it was focusing on operational forecasts for Helene, now a tropical storm, but “it’s either the highest or one of the highest,” said John Cangialosi, one of the center’s senior hurricane specialists.

The forecast of a “70-knot surge in 72 hours on Monday was one of the most aggressive forecasts” for a potential tropical cyclone, Cangialosi said.

“It’s an aggressive forecast for good reasons,” he said. “We’re trying to get ahead of the potential for rapid intensification before it gets to Florida.”

Helene is expected to make landfall along or near Big Bend, Florida, on Thursday evening, bringing widespread wind, rain and storm surge effects to the Southeast. The exact track and timing are still subject to change, the hurricane center said Tuesday.

Latest news about Helene: Florida braces for major hurricane

What computer models show in Helene’s prediction

The suite of computer models used to forecast storms indicate that some predict even stronger storms in Helene and that air pressure will drop dramatically, which could lead to the lowest storms ever recorded in the Gulf of Mexico.

These predictions are “probably a little bit over the top for what’s realistic,” Lillo said. The models face two challenges: Helene’s larger-than-average size and the still-sloppy organization on Tuesday afternoon.

“Larger storms tend to intensify a little bit more slowly, which puts a bit of a limit on the maximum intensity they can reach upon landfall,” Lillo said.

The models are struggling because the storm is not yet fully organized and remains lopsided, and most of the intense convective clouds are still east of the center, said David Roth, a meteorologist with the Weather Prediction Center. Helene did not officially become a tropical storm until 11 a.m. Tuesday.

The models are known to sometimes become “overly intense” in such situations, Roth said.

Fortunately, the hurricane center is aware of these kinds of biases that exist in the models, he said. For every model that predicts a super-intense storm, another model has a bias in the other direction, and they eventually cancel each other out as the official forecast is being prepared.

What does Helene predict for the future?

The hurricane center and the National Weather Service generally advise residents near a storm to expect a category higher than forecast. Helene is currently forecast to be a Category 3 inland, with winds of up to 115 mph.

Ultimately, the limiting factor for highest wind speeds and lowest pressures is the speed at which the circulation center organizes itself once it has formed.

“That’s what we’ve been waiting for the last 24 to 36 hours,” Lillo said. “Once it gets organized and tightens up, it can take advantage of the very high temperatures in the Gulf.”

Dinah Voyles Pulver is a climate change and environment writer for USA TODAY. She has covered hurricanes, tornadoes and severe weather for more than 30 years. Reach her at [email protected] or @dinahvp.