Helene is almost a hurricane. See how the path intensified

The forecast that Helene will develop from a potential tropical cyclone to a Category 3 hurricane appears to be the fastest development the National Hurricane Center has ever predicted for a low pressure system.

“They had never forecast a major hurricane within 60 hours for a sub-tropical storm disturbance,” said Sam Lillo, a meteorologist and software engineer at DTN Weather, based on a computer analysis of the center's historical forecast data. “The entire forecast is also fundamentally faster than you've ever seen for 36 hours and 48 hours from a tropical depression.”

The National Hurricane Center did not have those statistics on hand Tuesday because it was focusing on the operational weather forecast 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 prediction of a “70 knot increase in wind speed within 72 hours on Monday” is one of the most aggressive forecasts for a possible tropical cyclone, Cangialosi said.

“This is an aggressive forecast for good reason,” he said. “We are trying to get ahead of the potential rapid intensification before it reaches Florida.”

Helene is expected to make landfall along or near Florida's Big Bend on Thursday evening, bringing widespread wind, rain and storm surge impacts across the Southeast. However, its exact track and timing could still change, the hurricane center said Tuesday.

Latest news about Helene: Florida prepares for severe hurricane

What computer models show in Helene’s forecast

Some of the computer models used to forecast the storm continue to predict that Helene will strengthen further and that pressure will drop dramatically, causing the storm to have some of the lowest pressures ever recorded in the Gulf of Mexico.

These predictions are “probably a bit exaggerated compared to what is realistic,” said Lillo. The models face two challenges: Helene's above-average size and her still sloppy organization as of Tuesday afternoon.

“Larger storms tend to intensify a little more slowly, which somewhat limits the maximum intensity they could reach before landfall,” Lillo said.

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

It is known that the models sometimes become “overly intense” in such situations, Roth said.

Fortunately, the hurricane center is familiar with such biases in the models, he said. For every model that predicts an extremely strong storm, there is another model that is biased in the other direction, and those two models cancel each other out when producing the official forecast.

What does Helene’s future prognosis hold?

The Hurricane Center and National Weather Service typically advise residents in the path of a storm to prepare for a Category 3 storm higher than forecast. Helene is currently forecast to be a Category 3 storm with winds of 115 mph when it makes landfall.

Ultimately, the limiting factor for highest wind speeds and lowest pressure is how quickly the circulation center organizes itself once it has already formed.

“This is what we've been waiting for for the last 24 to 36 hours,” Lillo said. “Once it's organized and solidified, it can take advantage of the very hot temperatures in the Gulf.”

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

What computer models show in Helene’s forecast

What does Helene’s future prognosis hold?

Leave a Reply Cancel reply