Could Helene be a sign of things to come for future hurricanes?

Communities across the southeast US are reeling from the impacts of Hurricane Helene, which may be one of the country’s most devastating disasters on record.

The Category 4 hurricane made landfall in the rural Big Bend region of Florida with windspeeds of 225km/h on Thursday night – the most powerful storm on record to hit this region. It then weakened to a tropical storm as it moved north through Georgia, the Carolinas and Tennessee.

At least 116 people have been killed by Helene, according to local officials, with many hundreds more still missing. They fear there are more bodies to be discovered as rescue efforts continue. Georgia’s Governor Brian Kemp described the state as looking like “a bomb went off”.

Most of the deaths confirmed so far have been in North and South Carolina where heavy rainfall led to devastating flooding and landslides. Millions of people have also been left without electricity across the region.

Entire towns have been completely cut off in parts of west North Carolina and East Tennessee after floodwaters swept through, taking out bridges and major roads with them.

Governor of North Carolina Roy Cooper said the storm had brought “catastrophic devastation… of historic proportions”.

Though climate change didn’t necessarily cause Hurricane Helene, research suggests that may be supercharging storms like this with experts predicting a record number of strong storms at the beginning of the season.

Stronger storms with more deadly rain

The US Federal Emergency Management Agency (FEMA) has linked the severe impacts of Hurricane Helene to climate change.

“This storm took a while to develop but once it did it intensified very rapidly – and that’s because of the warm waters in the Gulf that’s creating more storms that are reaching this major category level,” FEMA Administrator Deanne Criswell told CBS show Face the Nation on Sunday.

These rising temperatures in the Gulf, she said, were causing conditions that led to “significant infrastructure damage” across multiple states. The FEMA administrator pointed out that a 4.5-metre storm surge had hit where Helene came ashore and almost 75cm of rain fell in western areas of North Carolina.

“In the past, damage from hurricanes was primarily wind damage, but now we’re seeing so much more water damage and that is a result of the warm waters which is a result of climate change,” Criswell said.

She added that she didn’t know if anybody could be fully prepared for the level of flooding and landslides North Carolina was experiencing.

What is climate change doing to hurricanes?

Though we tend to pay most attention to a hurricane’s wind speed, characterised by the Saffir-Simpson scale that gives them their category, it may not always be the most damaging consequence of a hurricane.

A lot of different factors – like ocean heat, winds, pressure and moist air – determine the strength and characteristics of a hurricane. This can make measuring the precise impact of climate change difficult but there are some things we know for sure.

More heat means more fuel for storms

These massive storms are fuelled by heat from the ocean, converting it into kinetic energy in the form of wind. Higher ocean temperatures mean more fuel for the storm’s engines.

According to the most recent report from the Intergovernmental Panel on Climate Change, the proportion of hurricanes that fall into the most intense Categories 4 and 5 are likely to increase as the planet warms.

Helene is the eighth Category 4 or 5 Atlantic hurricane to make landfall in the US in the last eight years. That’s as many of these intense hurricanes as hit the US in the prior 57 years.

Sea surface temperatures along the path Helene took through the Caribbean and Gulf of Mexico were around 1 to 2C higher than average, according to data from the NOAA’s Coral Reef Watch.

A warmer world means more rain

Scientists are pretty confident that climate change will cause storms like this to drop more rain too. For every 1C the atmosphere warms by, it can hold 7 per cent more moisture and more moisture in the air means more rainfall.

Scientific modelling predicts around a 10 to 15 per cent increase in rainfall rates on average within 100km of hurricanes if the world warms by 2C. And, as storms become stronger they don’t dissipate as quickly, meaning they may find their way further inland to drop this rain in places that aren’t prepared for the deluge.

More storms that intensify rapidly

Scientists think climate change is also causing rapidly intensifying hurricanes like Helene to become more common. These storms that strengthen quickly before landfall are dangerous because they can catch forecasters off guard and give local populations less time to prepare or evacuate.

Helene went from a Category 1 storm to a Category 4 storm in less than a day. It is one of 10 storms since 1950 that have strengthened by around 65km/h in the 24 hours before they made landfall. Five of those 10 storms have hit in the last seven years.

Rising sea levels make storm surges worse

Helene’s storm surge broke long-term records at many measuring stations along the west coast of Florida. Sea level rise contributed to these records being set and has accelerated over the last decade along the Florida coast. The city of St Petersburg, for example, has seen an average rise of 7mm a year.

A higher start point on top of stronger winds means a higher storm surge bringing more destruction to coastal communities.

What has happened during this year’s Atlantic hurricane season?

Despite forecasts for a record-breaking year, this hurricane season has actually been remarkably quiet.

Experts predicted that there would be between 17 and 24 storms with eight to 13 of those turning into Hurricanes. In July, Category 5 Beryl swept across the Caribbean and the US killing dozens of people. As the earliest storm of its size ever recorded, many believed it was a sign of things to come for this year’s Atlantic storm season.

But after Beryl, things were relatively quiet until Helene hit. So far numbers have been slightly below average with 10 named storms, six hurricanes and two months left until the end of the season.