How And Why A Rare Tornado Occurred On Cape Cod

By: Ellen Chahey

Meteorologist Phil Burt told the tale of Cape Cod’s July 23 tornado on Nov. 14 at Brooks Free Library. ED MARONEY PHOTO

'Weather Nerd' Phil Burt Explains

HARWICH – Tornado!?

That single word, complete with the astonished punctuation, was the first image in a PowerPoint talk on Nov. 14 at Brooks Free Library about the unusual event that pounded Harwich, Chatham, and some of the Upper and Mid Cape on July 23.

The speaker was Phil Burt, a self-proclaimed “weather nerd” who has a master’s degree in meteorology. “I’ve been addicted to weather since I was 3 or 4 years old,” he said.

“A meteorologist is lying to you if they say they’re happy a storm is pulling away,” he said to the laughter of a full house in the library’s Thornton Room. On tornado day, he said, “I went outside”—he was in Hyannis—“and I got really wet and I was really happy.”

Burt, who lives in Brewster, directs emergency services for Barnstable County.

He explained how tornadoes form, and then gave a nearly minute-by-minute account of the July event from 8:37 a.m., when he first posted a forecast of “rain” on what was then still a sunny day, until after 12:22 p.m, when the twister left Chatham and the sun came out again.

Tornadoes feed on several conditions in order to form, Burt said.

Most important, they need atmospheric instability, in which warmer air rises from the ground and hits colder temperatures aloft—which is not so common on the Cape because the ocean usually keeps the ground air cool—and they need wind shear, in which the wind goes in one direction on the ground, then shifts aloft, which is plentiful on the Cape. Add heat, moisture, and “a lifting mechanism” to get the warmer air up to meet the colder, and the stage can be set. All of these factors were present to some extent on July 23.

“A tornado can form anywhere on Earth,” Burt explained, “but ‘Tornado Alley’ (South Dakota, Kansas, Nebraska, Oklahoma, and north Texas) is almost the best on the globe,” followed by “Dixie Alley” (Arkansas, Louisiana, Alabama, and Mississippi).

However, “On July 23, no tornadoes were expected anywhere in the USA,” Burt said, “but it makes a lot of sense that we had one. We had very humid air, and a front from south of Long Island to Chatham. We were getting winds from two directions because some were going clockwise around high air pressure, and others were going counterclockwise where it was low.”

Also, there was warm air aloft, and warm air from the surface was trapped by it. “We were at the end of a heat wave, and we had wind straight from the west,” he said. “Chatham had a high of 96 degrees,” unusually hot.

At 9:05 a.m., air was starting to rotate off Long Island and there were forecasts of a possible waterspout there. By 10:38, the storm was starting to spin toward the Elizabeth islands. Just before 11, severe thunderstorm warnings were showing up, and at 11:03 the first “tornado vortex signature” appeared on the radar, meaning that it was “seeing stuff in the sky that’s not supposed to be there—limbs, trees, boards—like in 'The Wizard of Oz,'” said Burt.

At 11:13 the Cape got its first tornado warning, by 11:37 there was lots of wind damage in Popponessett, and by 11:39 there were “tornado warnings everywhere. “Kudos to the Weather Service for its quick communication,” Burt said, and for its “very, very good forecasting.”

Soon (11:55) the storm reached Lewis Bay and a gust of 91 mph was recorded at Kalmus Beach in Hyannis. It headed into South Yarmouth, which experienced a gust of 110. From noon on, the tornado, still at a maximum of 110, was knocking trees down in East Dennis, Harwich and Chatham until it veered off Chatham after 12:22 p.m.

Although there was a lot of tree damage wherever the tornado touched down, there were no fatalities, and “the entire state converged on Harwich” with help and resources, said Burt. “There is a lot of video out there on YouTube” that records the tornado and its aftermath. In response to a question from the audience, Burt said that there was no visible funnel.

Another questioner asked Burt how storm warnings are called. They’re made by a human, he said, based on the radar images tracked by computers. After the event, assessment of damages is generally done “from the ground” by emergency workers who drive to affected areas.

Burt's local weather website is capecodweather.net.

The library plans to follow-up Burt’s presentation with a “Community Conversation” at 2 p.m. on Thursday, Nov. 21, about extreme weather events. The goal is to discuss possible responses to such events as the tornado.

The “Community Conversations,” according to the library, are “lightly facilitated discussion groups that will provide an easy structure for engaging in friendly yet meaningful” exchange about issues of common interest.

The program is free, but registration is required in order to plan for refreshments. Call the Brooks Free Library, at 739 Main St., at 508-430-7562.