Hurricanes that make landfall are taking more time to weaken – and climate change may be to blame.
Researchers found that because of rising sea temperatures, the average North Atlantic hurricane now takes 33 hours to lose steam, compared to the 17 hours some 50 years ago.
Storms forming over warmer oceans are carrying moisture as they approach land, which gives them enough fuel to keep their strength after it comes ashore.
The team says as the world continues to warm, hurricanes will have the power to travel farther and devastate more communities inland.
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Storms forming over warmer oceans are carrying moisture as they approach land, which gives them enough fuel to keep their strength after it comes ashore. Last month, Hurricane Zeta (pictured) covered more than 1,000 miles of land before losing power.
The stark warning comes from scientists at the Okinawa Institute of Science and Technology Graduate University (OIST).
Hurricane season in the Atlantic Ocean typically begins in early June and finishes at the end of November, but 2020 has been the busiest season in the 170-year record –with 29 hurricanes to date.
These furious weather events typically travel up to 100 to 200 miles inland, where it then weakens to a tropical storm with winds ranging from 39 to 79 miles per hour.
However, Hurricane Camille, which hit in 1969 traveled nearly 350 miles inland before downgrading to a tropical storm.
The team used computer simulations to test the link between warmer sea surface temperature and slower weakening of hurricanes that reached land, which allowed them to set different temperatures during the study
And last month, Hurricane Zeta covered more than 1,000 miles of land before losing power.
Professor Pinaki Chakraborty, senior author of the study, said: ‘We know that coastal areas need to ready themselves for more intense hurricanes, but inland communities, who may not have the know-how or infrastructure to cope with such intense winds or heavy rainfall, also need to be prepared.’
Scientists around the world have conducted a number of studies that show climate change plays a role in how strong a hurricane becomes as it travels over the open ocean.
But this is the first study to uncover a clear link between a warming climate and the small group of storms that have made landfall.
Chakraborty and his team analyzed North Atlantic hurricanes that made landfall over the past 50 years and found that over the first day the storms hit land, they weakened nearly twice as slowly as they did five decades ago.
Lin Li, first author and PhD student in the OIST Fluid Mechanics Unit, said: ‘When we plotted the data, we could clearly see that the amount of time it took for a hurricane to weaken was increasing with the years.’
‘But it wasn’t a straight line — it was undulating — and we found that these ups and downs matched the same ups and downs seen in sea surface temperature.’
The team used computer simulations to test the link between warmer sea surface temperature and slower weakening of hurricanes that reached land, which allowed them to set different temperatures during the study.
Once each virtual hurricane reached category 4 strength, the scientists simulated landfall by cutting off the supply of moisture from beneath.
Researchers found that because of rising sea temperatures, the average North Atlantic hurricane now takes 33 hours to lose steam, compared to the 17 hours some 50 years ago. The data shows the study examined 71 hurricanes simulations
‘Hurricanes are heat engines, just like engines in cars. In car engines, fuel is combusted, and that heat energy is converted into mechanical work,’ Li explained.
‘For hurricanes, the moisture taken up from the surface of the ocean is the ‘fuel’ that intensifies and sustains a hurricane’s destructive power, with heat energy from the moisture converted into powerful winds.’
‘Making landfall is equivalent to stopping the fuel supply to the engine of a car. Without fuel, the car will decelerate, and without its moisture source, the hurricane will decay.
The computer simulations all showed the same result – a storm that developed over warmer water took more time to lose power over land.
‘These simulations proved what our analysis of past hurricanes had suggested: warmer oceans significantly impact the rate that hurricanes decay, even when their connection with the ocean’s surface is severed. The question is -why?’ said Chakraborty.
This is when they realized the key was the stored moisture.
Even thought a hurricane does not have the ocean to supply moisture when it hits land, the reserved stock that it gathered is enough to keep the storm going.
When the scientists created virtual hurricanes that lacked this stored moisture after hitting land, they found that the sea surface temperature no longer had any impact on the rate of decay.
Hurricane Camille, which hit in 1969 traveled nearly 350 miles inland before downgrading to a tropical storm
‘This shows that stored moisture is the key factor that gives each hurricane in the simulation its own unique identity,’ said Li.
‘Hurricanes that develop over warmer oceans can take up and store more moisture, which sustains them for longer and prevents them from weakening as quickly.’
Along with fueling hurricanes, the stored moisture makes them ‘wetter,’ which allows the storm to unleash devastatingly high volumes of rainfall on coastal and inland communities.
The study also pinpoints issues with the simple theoretical models widely used to understand how hurricanes decay.
‘Current models of hurricane decay don’t consider moisture -they just view hurricanes that have made landfall as a dry vortex that rubs against the land and is slowed down by friction,’ said Li.
Our work shows these models are incomplete, which is why this clear signature of climate change wasn’t previously captured.’