A new scientific study shows that tropical cyclones are moving more slowly than in years past.
While wind speeds have actually intensified within such storms – producing more category 5 storms in recent years – the rate at which they move over sea and land has dropped by 10 percent, compared to 60 years ago, according to a study that appeared Wednesday in Nature magazine.
While Hurricane Harvey was not part of the study, which looked at 2016 storms, it is being used as an example of the trend pointed out by the data. Harvey, which struck Houston last year, lingered over the region for days, dropping up to 50 inches of rain in some areas.
If such a trend continues, said Simon Boxall, spokesman for Hazard Management Cayman Islands, it means those living here need to boost their planning for the advent of a hurricane.
“It reinforces the message that we have to prepare,” Mr. Boxall said. “If new systems are moving slower, that tends to bring more impact.”
Initially, he said, residents should not count on assistance from the government but should be ready to fend for themselves for several days.
“We recommend three to five days at a minimum,” Mr. Boxall said. “Obviously, we’d like people to be more prepared than five days. With Ivan [the 2004 hurricane that devastated much of Grand Cayman] no water came out of the taps for a month.”
He said the islands are better prepared in many ways than they were in 2004. The department has pushed the development and training of community response teams and other types of post-storm support.
“We’ve got a relief plan, which we didn’t have before,” he said. “We’ve got money in the bank to fund the recovery and reconstruction. Still, we remain vulnerable.”
Storms worldwide in 2016 moved about 1.25 mph slower than those in the 1940s and 1950s, said the study, which was conducted by the U.S. National Oceanic and Atmospheric Administration’s Cooperative Institute for Meteorological Satellite Studies in Madison, Wisconsin. The effect was strongest over land, with speeds decreasing 20 percent over Australia and coastal areas in or near the North Atlantic.
Study author James Kossin started his research before the 2017 season, stopping his analysis at 2016. Adding last year’s storms would have made the slowdown a bit more prominent, he said.
Unhurried hurricanes also mean strong winds blowing more often over the same place and possibly more storm surge, Mr. Kossin said.
The trend has all the signs of human-caused climate change, Mr. Kossin said. But the study did not look at causes by using computer models to simulate the Earth with and without warming. It is based solely on past observations, he said.
Another study that came out recently, using computer models, concluded that future storm movements will slow because of climate change.
Climate change is tinkering with and slowing down atmospheric circulation patterns – the wind currents that move weather along, Mr. Kossin said.
Steering winds that move hurricanes along are slowing, he added, due to a diminished temperature difference between the tropics and the poles.
The Associated Press contributed to this story.