Since 2017, an unprecedented number of storms classified as Category 4 or stronger have hit the US coastline: Harvey, Irma, Maria, Michael, Laura, Ida and now Ian. They all qualify as “rapid intensification events,” when storm winds increase by at least 35 mph in 24 hours.
The number of these types of storms has increased in recent decades. Sixteen of the twenty hurricanes over the past two seasons in the Atlantic basin experienced rapid intensification.
“Especially in the area near the coast where the cyclone was just before making landfall, what we’re seeing is that the cyclone intensification rates have escalated,” said Karthik Balagoro, a climate scientist at the Pacific Northwest National Laboratory. “This is a bit frustrating.”
Ian was only the most recent case when her winds nearly doubled over a 24-hour period, going from a low-level hurricane with sustained winds of 75 mph on Monday to a Category 3 storm with 125 mph winds on Tuesday. Then, as it approached Florida on Wednesday, its winds rose even faster, moving from 120 mph around 2 a.m. to 155 mph by 7 a.m.
The string of severe tornadoes that have hit the United States since 2017 is “one of the busiest times for strong tornadoes we’ve seen historically,” said Phil Klotzbach, a senior researcher at Colorado State University. A similar period of hurricane activity came from 1945 to 1950, when five Category 4 hurricanes hit Florida in six years, leaving Klotzbach reluctant to describe the series of severe storms since 2017 as unprecedented.
Klotsbach added that a period of rapid reinforcement is roughly a prerequisite for a storm to become among the strongest. “The stronger the storm, the more likely it is that it will experience rapid intensification,” he said.
However, recent research suggests that the height of rapidly intensifying storms has a profound effect.
One A study published earlier this year It found that since 1990, a steadily increasing number of global tropical cyclones have undergone what the study called “extreme rapid intensification,” with winds increasing by at least 50 knots, or 57 miles per hour, over a 24-hour period. else Study from 2018 Focusing on the Atlantic Basin, it found that among the hurricanes that consolidated the fastest, their rates of intensification accelerated, increasing by about 4 miles per hour each decade over the past 30 years.
Intergovernmental Panel on Climate Change Latest review He came to a similar conclusion, finding that tropical cyclones may become more intense and prone to rapid intensification.
“I would say one of the most worrying things about climate change is the change in extremes,” Balagoro said. “Quick condensation is a process that fits that extreme category.”
For example, Balagoro said, if a storm in the Caribbean four decades ago intensified by 34 mph, the same storm would increase by about 48 mph in today’s climate.
And a preliminary analysis of precipitation Ian Thursday released Written by Kevin Reed Professor Stony Brook University and Lawrence Berkeley National Laboratory Senior Scientist Michael Weiner, Based on peer-reviewed research, climate change has been found to be responsible for a 10 percent increase in extreme precipitation in Ian.
Hotter ocean, along with lower vertical wind shear, It helped drive the rapid intensification of recent storms.
In general, ocean waters must be above 79 degrees Fahrenheit for a hurricane to develop and persist. In recent decades, the ocean temperature has increased Standard rates Because of the greenhouse gases emitted by humans, making this threshold easier to reach. When Ian was moving away from Cuba, sea surface temperatures were approaching 86 degrees.
Rising global air temperatures also mean that water, especially in bodies like a bathtub in the Gulf of Mexico, is warming far beyond their surface. The deeper that warmth gets, the more fuel can flow into a slow-moving storm like Ian. Warm sea water evaporates and pumps moisture into the air, which can condense into storms, clouds, and rain.
said James Kosin, chief scientist for the Climate Service, a risk assessment advisor and a former scientist at the National Oceanic and Atmospheric Administration who led studies on hurricane intensification.
Vertical wind shear — changing wind speeds and direction at different altitudes in a storm — is also a major influence on hurricane intensity, although researchers are still considering any long-term trends. High wind shear can weaken a tornado, while weaker shear can help create and strengthen a tornado.
Wind shear has been relatively low in the western Atlantic since 2017, a factor that has contributed to the outbreak of tropical cyclones since then, According to Klotsbach. It is possible that long-term climate change will make this environmental condition more common. Scientists hypothesize that the jet stream, which creates strong wind shear, could be pushed north as global temperatures rise.
Climate change may also increase the potential for hurricanes to intensify — and devastate — by slowing them down, and by increasing the duration of damaging winds and inundating rain.
For example, while Hurricane Ian took a similar path, and of similar intensity, as Hurricane Charlie in 2004, Charlie exploded in Florida at 20 mph, while Ian moved at only half the speed. That allowed Ian to shed up to 20 inches of rain along his path, according to initial estimates, already more than twice as much as Charlie’s.
Scientists hypothesize that the slow movement of storms may result from rapid warming at the Earth’s poles, as this has narrowed the gap in temperature and pressure from the poles to lower latitudes. These differences drive winds around the world, pushing around weather systems, including hurricanes, like corks in a stream. So when they are reduced, it could cause a broader slowdown in global weather systems.
The same phenomenon may cause bouts of extreme heat and explosions of polar cold, because the jet stream winds that normally break weather patterns and drive storm systems are weaker.
“It seems that the entire atmosphere is getting slower, so the storms that carry them are moving more slowly,” Kosen said.
Storms that move slower are able to drop huge amounts of rain. Hurricane Harvey dumped more than 60 inches of rain in some parts of southeast Texas as it lay over the area for about two days.
Likewise, if a storm carrying hurricane-force winds stays over one spot long enough, “it will eventually flatten everything,” Kosen said.
Meteorologists said the authorities have changed the way they issue forecasts and warn the public, Because of the danger posed by the sudden escalation of the storm.
The National Hurricane Center noted concerns about rapid intensification with Ian once the storm developed into a tropical storm. On Friday morning, long before Ian approached the Cayman Islands and Cuba, meteorologists warned that he was likely to feed on the warm waters of the Gulf of Mexico and would become a major hurricane approaching Florida within five days.
“We have much better tools to be able to predict this rapid intensification than we did previously,” Klotsbach said. “The models are only better.”