A new normal? Climate change is bringing more extreme weather — including floods — to Vermont

When Hurricane Beryl formed above the Atlantic Ocean in late June, it soon became the earliest Category 5 hurricane in the National Oceanic and Atmospheric Administration’s records, which date back to 1851.

Beryl traveled through the Caribbean before making landfall in Mexico on July 5, then traveled northeast, from Texas to New England. By the time it reached Vermont on July 10, it was considered a post-tropical storm — but combined with stormfronts that already existed in the area, it wreaked havoc.

The storm entered Vermont in Addison County, then traveled northeast, dropping more than seven inches of rain in some areas, damaging homes in municipalities including Plainfield, Barnet and Barre, and tearing roads apart in many other towns.

Beryl’s arrival in Vermont — exactly one year after catastrophic flooding hit Vermont in July 2023, and about seven months after heavy rains caused more flooding in December — reopened a wound that, for many, had barely healed.

The timing also raised the question: In a changing climate, is this Vermont’s new normal?

Storms that cause destructive flooding are not likely to hit Vermont every single year, according to Matthew Rosencrans, lead hurricane season forecaster at NOAA’s climate prediction center.

“But if you look across 10 or 20 years, you’re going to have a slightly higher percent chance of these events happening,” he said.

This year, forecasters expect the storm season to be more active. NOAA predicts an 85% chance that the 2024 hurricane season, which began on June 1 and ends on Nov. 30, will be “above-normal” and include four to seven major hurricanes.

But that doesn’t mean more extreme flooding is expected to hit Vermont this summer.

Overall, Vermont has a 33 to 40% chance of experiencing above normal precipitation for the remainder of the hurricane season, Rosencrans said, so “just a very slight tilt towards above-normal precipitation.”

Meteorologists expect southern Vermont to receive about half an inch more precipitation than normal for August, September and October, the core of the hurricane season, he said. In northwestern Vermont, the administration predicts that precipitation will be normal.

Record-warm ocean temperatures

Beryl became a record-breaking storm because of “the record warm sea surface temperatures in the Atlantic,” Rosencrans said. At times, ocean surface temperatures have been recorded at 3 degrees above normal.

The Atlantic Ocean is experiencing record heat for several reasons. The first is a naturally occuring warm cycle. Ocean temperatures in the Atlantic oscillate regularly between warm and cool cycles, with one phase typically lasting for several decades .

The second factor is La Niña , a climate pattern during which trade winds move warm water in the Pacific Ocean to the west, prompting cold water in the eastern Pacific to come to the ocean’s surface. That dynamic pushes the jet stream north, and can change air pressure systems over North America. It also reduces wind shear — changes in wind speed or direction over a short distance — and cloud cover over the Atlantic Ocean, warming the water and creating conditions that are favorable for tropical storms.

Episodes of La Niña and its opposite, a climate pattern called El Niño, typically last nine to 12 months, according to NOAA, but can last longer.

Finally, ocean temperatures are warmer because of climate change. When people burn, produce and transport fossil fuels, pollutants including carbon dioxide and methane enter the atmosphere and trap the sun’s heat. The more pollutants that are trapped, the warmer the atmosphere — and the ocean — become.

“When we talk about a change in climate, we’re seeing that the oceans are storing heat as well, and not just the surface of the oceans, but also the oceans at depth,” said Lesley-Ann Dupigny-Giroux, Vermont’s state climatologist.

That’s important in the context of hurricanes, which are “heat engines,” she said. The water below them needs to be a certain temperature for the storms to grow and become stronger.

Last year’s ocean temperatures broke records, too, Rosencrans said. In most years, ocean temperatures haven’t deviated more than one degree from the average temperatures. There are only two years when the ocean temperatures have risen two and three degrees above average: 2023 and 2024.

“Last year, when we were thinking about hurricanes in 2023, and we saw so many hurricanes and so many powerful hurricanes, it was important to note that it was also an El Niño year,” Dupigny-Giroux said. “And El Niños usually lead to fewer hurricanes.”

Hurricane Beryl differed from last July’s storm , which included “different types of warm fronts, cold fronts, low pressures, troughs, moisture all coming together and just spinning in place over Vermont,” Dupigny-Giroux said.

Vermont’s topography influenced the impact of this summer and last summer’s major storms. If a storm hits a mountain in a perpendicular direction, it’s forced to rise, which prompts more precipitation, Dupigny-Giroux said. When a river valley has steep mountains on either side, the valley could keep the storm moving within its walls, focusing the rainfall in one particular area. That dynamic has played out multiple times in Barre, she said.

Towns along the spine of the Green Mountain are particularly vulnerable, she said, but flooding can happen anywhere.

Vermont’s repeated flooding, along with the higher risk of storms in the coming years, is “a blatant reminder that we need to be preparing for these kinds of things ahead of time as much as we can to really minimize those damages,” Rosencrans said.

Dupigny-Giroux grew up in the Caribbean, and there, everyone learned a saying to help them remember when storms were most likely to hit, she said. It went, “June, too soon. July, standby. August, come it must. September, remember. October, all over.”

“We’re probably gonna have to change that saying with our changing climate,” she said, “because June is no longer too soon.”

Read the story on VTDigger here: A new normal? Climate change is bringing more extreme weather — including floods — to Vermont .