Tornado Alley enters new territory

A hurricane that tore through the Houston area on Tuesday was the type of early-season storm that scientists say is occurring with increasing regularity—a sign that severe weather conditions are changing.

The hurricane struck Pasadena, southeast of Houston, severely damaged homes and other buildings, and cut off electricity to thousands of people in and around the city. Although not yet confirmed by the National Weather Service, more than a dozen other hurricanes have been reported as the storm moved along the Gulf Coast.

The number of reported hurricanes adds to the changes that experts have observed in recent years—specifically, where and when hurricanes occur began to change.

Historically, hurricanes were more likely to strike in a column of the central US nicknamed “Tornado Road.” The region includes parts of Texas, Oklahoma, Kansas, and Nebraska. But in recent years, researchers have noticed fewer hurricanes landed on the Great Plains and more hit the Southeast.

Victor Gensini, associate professor of earth, atmosphere and environment at Northern Illinois University, who published an important study on the subject in 2018 and comprehensively examined change, said that the changing boundaries of Tornado Alley could have deadly consequences.

“The #1 thing is that we have more population density in the Mid-South,” Gensini said. “Basically there are more targets to hit on the dartboard.”

Diverse landscapes are also a factor in the destructiveness of a storm. In areas with congested cities, lots of trees and less open space, a hurricane, for example, can cause more devastating damage.

Residents drive past damaged apartment complex after a storm system sweeps Deer Park, Texas (Elizabeth Conley/Houston Chronicle via AP)

Residents drive past damaged apartment complex after a storm system sweeps Deer Park, Texas (Elizabeth Conley/Houston Chronicle via AP)

There are also more vulnerable communities in the Southeast, especially among people living in mobile homes, Gensini said.

“Half of tornado deaths happen in mobile homes,” he said. “If you live in a mobile home during a hurricane warning, it’s too late. This is a huge vulnerability.”

Hurricanes can develop at any time with the right atmospheric components, but they typically intensify in a season that runs from March to June. Increasingly, however, such storms are returning earlier in the year, usually in months not associated with strong hurricane activity.

Gensini said the first three weeks of 2023 already have some of the highest tornado numbers reported for this time of year.

“We are well above average in terms of the number of tornadoes we expect for January,” he said.

One of the main reasons for a stormy start to the year is a naturally occurring climate pattern known as La Niña, in which colder-than-average water in the Pacific Ocean affects weather systems around the world.

Both La Niña and its warmer counterpart, El Niño, affect the position of the jet stream, powered by temperature differences between the colder polar region to the north and warmer air masses to the south. Scientists think changes in the jet stream may help explain the increase in storms — increased atmospheric instability likely impacting areas below the fast-moving airflow — but it’s still an active area of ​​research.

“The jury is still a bit undecided on this, but this is the kind of preliminary hypothesis our group is trying to test,” Gensini said.

While detecting the specific effects of climate change on hurricanes is more difficult than with other extreme weather events such as hurricanes, global warming may also be a factor, experts said.

People run under downed power lines after a hurricane hits Pasadena, Texas (via AP Mark Mulligan/Houston Chronicle)

People run under downed power lines after a hurricane hits Pasadena, Texas (via AP Mark Mulligan/Houston Chronicle)

Christopher Weiss, a professor of atmospheric science at Texas Tech University, said part of the difficulty arises because studies suggest competing effects.

As the Earth warms, atmospheric instability will increase, creating more favorable conditions for storms to develop. However, at the same time, severe wind shear, where winds increase and change direction rapidly at different atmospheric heights, is predicted to decrease as a result of climate change. Weaker wind shear can reduce the amount of warm air rising in storms and therefore suppress hurricane formation. Scientists are still trying to understand what these seemingly contradictory results might mean for hurricanes, but studies suggest a warmer climate will produce more storms, Weiss said.

“Even if wind shear remains fairly stable, we are increasing instability on top of that, so we can expect to see more in the path of hurricane formation,” he said.

Next month, Weiss and his colleagues will begin a three-month research project in the Southeast focusing on studying storms in the region and how to develop estimates of when they form. Weiss said the research, which is part of the National Oceanic and Atmospheric Administration’s VORTEX program, will also examine societal aspects, including existing refuges and how threats will be communicated to at-risk communities.

“It’s a really holistic approach to the hurricane threat in that part of the country, so hopefully we can have some impact,” he said.

With the year already getting off to an active start, the project may be well-timed.

Gensini said La Niña conditions will likely continue to feed atmospheric instability, which could mean more hurricanes going forward.

“It’s pretty rare to see an active January and February that suddenly gets dull in April and May,” he said. “When you look at hurricane statistics, if it starts in January and early February, it usually continues.”

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