Why did Hurricane Milton produce such powerful tornadoes?

Hurricane Milton Supercell storms — which can produce rotating updrafts and tornadoes — brought an expected dose of chaos before making landfall this week as they move through the state.

The resulting upheavals led the National Weather Service to issue 126 tornado warnings, and the agency's Storm Prediction Center issued 45 preliminary tornado reports.

5 people died in St. Lucie County after a tornado hit a retirement communityThe tornado was responsible for about a third of the 17 deaths reported so far.

As Florida begins the long process of cleaning up and recovering from Hurricane Milton, tornado outbreaks have emerged as a leading cause of death and damage in a state accustomed to tropical storms but less familiar with powerful tornadoes.

In what will likely go down as one of the worst tornado outbreaks ever seen during a hurricane in Florida history, the day included one of the strongest tornadoes in South Florida history.

Winds gusting up to 225 km/h hit Palm Beach Gardens, toppling concrete walls and ripping off large sections of roofs from newly built homes. National Weather Service preliminary report.

“This is the first EF-3 recorded for our area in South Florida from and south of Lake Okeechobee,” said Donal Harrigan, NWS meteorologist in Miami. An EF-3 refers to a tornado with winds estimated between 136 and 160 mph (EF stands for Enhanced Fujita Scale, which became Effective for the National Weather Service in 2007)

It's possible that several other observed twisters will be classified as EF-3 after damage assessment, Harrigan added.

“You can probably count on one hand how many EF-3s the state has had historically. We can probably have more than one of them a day,” he said.

Overall this year, the United States has seen an unusually high number of strong tornadoes associated with hurricanes.

Although tornadoes are common when a cyclone makes landfall, most are on the weaker end of the spectrum; Less than 1% of tornadoes associated with tropical systems that make landfall are rated EF-3 or stronger. This year, by contrast, four of the five hurricanes that made landfall in the United States produced tornadoes of EF-3 intensity.

From 1995 to 2023, only five tornadoes produced by tropical storms have rated highly.

Preliminary research suggests that tropical cyclones may produce more tornadoes in a warming world. In a study published in June, researchers modeled Ivan, Katrina, Rita and Harvey in a warmer future climate. Their results indicate the number of potential tornado storms produced by tropical cyclones will increase from 56% to 299% by mid-century assuming the rate of fossil fuel pollution remains constant.

It's not yet known whether climate change played a role in this year's storm-related upheavals. But Bill Gallus, author of the June study and professor of meteorology at Iowa State University, said it was “really unusual how unstable conditions were in South Florida” during Milton.

Conditions are considered unstable when differences in density and temperature allow pockets of air to rise and fall rapidly – ​​conditions that allow lightning.

“I was shocked when I opened the volatility chart. It was as loud as you would see in Kansas on a storm chase,” Gallus said. “Our hurricanes have produced more tornadoes, but never so many in Florida.”

He added that in a warming world, such instability “expects it to become more common.”

One of the reasons Milton produced so many tornadoes was because the hurricane's storm surges were far from its center.

“With the initial tornado, that particular Milton band of rain and thunderstorms seemed to be very far from the tornado,” Gallus said.

This outer band of storms separated and ended without interference from other systems – it was the storms that generated the tornado. It's a reminder that hurricanes can be a threat long before they make landfall and far from the center of the storm, experts said.

Other important ingredients for the Milton tornado: heat. The hurricane made landfall in Florida in the afternoon, and due to the storm track at the hurricane's edge, they encountered particularly warm conditions, as well as wind shear – changes in wind direction and speed at altitude. This allows them to be more powerful than the more common Hurricane configuration.

“There was plenty of time for the atmosphere to warm,” Gallus said. “In most hurricanes, you don’t get a lot of heat from the sun, tornadoes are frequent in heavy rain.”

In hurricanes with winds that rotate counterclockwise, like Milton, tornadoes form at the leading edge of the storm and to its right – sometimes called the dirty side. This area tends to see the worst wind.

That's how it happened in Milton's time, Gallus said: Twisters “happened where we see most tornadoes.”

But in Milton's case, he noted, the tornado was particularly concentrated.

Because of Milton's short path across the Florida peninsula, Gallus said, “the space that the tornado was producing was small — I think it's the most concentrated outbreak of tornadoes produced by a hurricane.”

More research is still needed on how climate change may affect tornadoes produced by hurricanes. But the impact of global warming on extreme precipitation is more difficult and obvious.

A report released Friday by the World Weather Attribution Project — a consortium of scientists that analyzes extreme weather and is considered an authority on determining the impact of climate change on specific events — found that rainfall in single-day events like Milton they are now about 20% to 30% more intense due to climate change. The analysis found that wind speeds in Milton were likely 10% stronger due to the effects of climate change.

The team also found Hurricane Helen to be wetter and windier due to climate change. another Preliminary report found that climate change may have increased Helen's rainfall by up to 50% over a three-day period in some of the hardest-hit areas.