Hurricane Milton was expected to bring storm surge. Where did the tornadoes come from?

Dozens of tornadoes spawned by Hurricane Milton caught many Floridians by surprise as they braced for heavy rain, strong winds, and storm surges. Violent twisters were seen crossing highways, ripping off roofs, and downing trees and power lines.

When Debbie Jones felt a drop in pressure and her ears popping in the Holiday Pines neighborhood of Ft. Pierce, she knew it was a tornado.

“All of a sudden, the power went out. I started hearing the wind pick up and debris start hitting very loudly. So I cranked the hurricane shutters shut and bolted out of there with them,” said Megan Brown, whose boyfriend is Ms. Jones’ son. The family barricaded together with their four dogs in the back of the house away from windows.

There have been 38 preliminary eyewitness reports of tornadoes in Florida since the night of Oct. 9, according to the National Oceanic and Atmospheric Administration Storm Prediction Center. The state sees 50 tornadoes on average total in a whole year. The number confirmed is expected to rise over the coming days as damaged sites are assessed.

“Certainly that will be a notable part of this storm, was how many tornadoes occurred within such a short period,” said Matthew Elliott, warning coordination meteorologist at the Storm Prediction Center.

Five deaths related to tornadoes occurred in the Spanish Lakes Country Club near Fort Pierce, on Florida’s Atlantic Coast, according to authorities. At a White House briefing, Homeland Security Secretary Alejandro Mayorkas said there were reports of as many as 10 fatalities from tornadoes, but he cautioned that the number was tentative.

Eyewitness reports came as the National Weather Service issued 126 tornado warnings yesterday in the state.

The ferocity of the twisters was also an unusual aspect of Milton.

“It’s definitely out of the ordinary,” said Northern Illinois University meteorology professor Victor Gensini. “Hurricanes do produce tornadoes, but they’re usually weak. What we saw today was much closer to what we see in the Great Plains in the spring.”

Conditions for breeding tornadoes were particularly favorable. Hurricane Milton spent the day offshore with warmth from the sun and instability in the atmosphere creating the right environment.

Tornadoes spawned by hurricanes and tropical storms most often occur in the right-front quadrant of the storm, but sometimes they can also take place near the storm’s eyewall, according to NOAA. The heat and humidity present in the atmosphere during such storms and changes in wind direction or speed with height, known as wind shear, contribute to their likelihood.

“There’s an incredible amount of swirling going on,” Mr. Gensini said of the conditions that allowed for the twisters to grow. “Those tornadoes were just in a very favorable environment.”

Earlier this year, Hurricane Beryl spawned 65 confirmed tornadoes, across several states. The most ever caused by a hurricane was 118 from Ivan in 2004. The difference is the tornadoes from Milton all came in Florida and over just eight to 10 hours.

Teasing apart the the damage caused specifically by Milton’s tornadoes could be complicated, but scientists say keeping accurate records of tornadoes is important.

Tornado activity can be grouped into three seasons: spring, tropical cyclone season, and late fall and winter. “It really goes to show that tornadoes can be a significant part of a tropical cyclone, in this case, a Category three hurricane,” Mr. Elliot said.

The warming of the oceans by climate change is making hurricanes more intense, but Mr. Gensini said he did not know of any connection between human-caused warming and the deadly tornadoes that Floridians experienced with Milton.

Florida has more tornadoes per square mile than any other state. But they’re usually not as severe as those in Midwest and Plains. However, a big outburst of powerful twisters killed 42 people and injured over 260 in Central Florida in the space of a few hours in February 1998.

This story was reported by The Associated Press.