Tropical cyclones that strengthen quickly likely to be more common
It’s a nightmare scenario that keeps forecasters up at night: A tropical cyclone strengthens quickly over a 24-hour period.
It happened last year with Hurricane Laura, which evolved from Category 1 to a more devastating Category 4 before striking near Lake Charles, La., sweeping buildings from foundations and killing seven people with surf and falling trees.
Researchers in the latest report from the Intergovernmental Panel on Climate Change agree it’s likely that tropical cyclones that formed over the past four decades increasingly went through such rapid intensification. They also say a greater proportion of future hurricanes very likely will be Categories 4 and 5.
Coastal communities need to prepare, experts say.
The trend toward a greater frequency of storms getting stronger rapidly may continue, said Texas State Climatologist John Nielsen-Gammon. Unexpected high winds and storm surges can cause disaster. Strong winds leave communities powerless, and storm surges kill.
But evacuating vulnerable areas requires time; doing so too hastily can be dangerous.
“That’s really the nightmare scenario for forecasters and emergency managers,” said Robert Rogers, a research meteorologist with the National Oceanic
and Atmospheric Administration who studies storm intensity changes. “Imagine a tropical storm that’s approaching landfall, maybe a 55 mph tropical storm, and it undergoes rapid intensification to become a 130 mph monster at landfall. That’s really what keeps the forecasters up at night. That’s really what a lot of our effort is going toward trying to better understand.”
NOAA scientists recently found that while predictions of a storm’s path have improved dramatically over recent decades, the accuracy of predictions about their intensity improved little until 2010. How intense a storm is reflects how fast its winds are. Forecasting this is challenging because both largeand small-scale factors are at play, and it’s hard to gather all the data, Rogers said. One can’t fly to ocean level in the eye of a hurricane.
The potential ramifications of getting this wrong, though, are significant.
Stronger storms bring with them damaging winds that can rip off rooftops, snap trees and topple power lines. They can also shove storm surges ahead of them, the prominent reason for evacuating. (Lower-category storms can bring devastating surges, too.) But evacuating ideally occurs over days: Harris County emergency officials prefer to ask people to leave at least 80 hours before a storm hits.
Meanwhile, climate change has altered the disasters that communities face. Sea levels have risen, meaning storm surges may cause more damage.
The ocean has warmed, one factor to consider for rapid intensification. That’s still an area of study: IPCC researchers reported “limited evidence” so far that human-caused climate change affected the intensities of strong tropical cyclones that were analyzed.
Whether it happens with every storm, local officials need to keep in mind that rapid intensification is possible and account for it in their planning, said emergency management expert Samantha Montano, an assistant professor at Massachusetts Maritime Academy. She advised considering “the worst that could happen, rather than necessarily what we know will happen.”
As it stands, local weather officials rely on conventional wisdom in preparing for one hurricane category higher than expected, not more. The way emergency officials do long-term planning for potential storms may also be outdated. Assessing the likelihood of a certain danger was typically based on what storms occurred in the past, not what climate science predicted
was coming, said Francisco Sanchez, Harris County’s deputy homeland security and emergency management coordinator.
People also need to be ready to believe a catastrophic forecast, Sanchez said.
“We can’t pretend or rely on our past experiences,” Sanchez said. “We have to recognize that each disaster is different. And if it’s telling us it’s going to be catastrophic, if it’s telling us it’s going to be like something we’ve never faced before, we need to take it at its word and act accordingly.”
Residents may not have five or six days to prepare for and evacuate from a storm, said Jeff Lindner, meteorologist for the Harris County Flood Control District.
Three-quarters of storms that struck Texas since 1852 developed and hit within 60 hours, he said. Rapid intensification can add pressure to that timeline. Hurricane Humberto in 2007 famously went from tropical depression to tropical storm to hurricane in 19 hours, hitting east of High Island.
Other memorable storms intensified rapidly too: Ike’s winds in 2008 went from tropical storm-level to Category 4 in a 24hour period when it formed, according to satellite estimates, but weakened before hitting Galveston with deadly surge. Harvey in 2017 rapidly strengthened to a Category 4 before striking near Rockport and later drenching the Houston area, unleashing catastrophic flooding.
What terrifies Jim Blackburn, an environmental attorney and longtime climate advocate, is the scenario where people feel equipped to handle what they think is coming and are caught off guard when it becomes something else. He worries about coastal residents dying because they prepare to ride out a small storm — and a much stronger one hits.
“People have assumed or have fallen into routines based on the past,” Blackburn said, “and that’s the whole point of climate change. You cannot depend on the past to predict the future.”