This enhanced NOAA satellite image was taken at 9.15 pm EST on Tuesday (Image: NOAA)

The second hurricane of the Atlantic season, hurricane Katia, has swung north and east and is heading for the UK. New Scientist explains what is happening and why.

What is Katia going to do, and what will happen in the UK?

Katia is currently off the east coast of the US and moving north-east, according to the National Hurricane Center in Miami, Florida. At present it is a category 1 on the Saffir-Simpson scale of hurricane strength – about as weak as a hurricane gets.

Over the weekend it will head east over the Atlantic to strike the UK on Sunday night. The British Met Office has issued severe weather warnings for the north and west of the country, beginning at midnight on Sunday night. It’s not clear which areas will be hit, but gale-force and even storm-force winds are expected.


By the time it reaches the UK, Katia will no longer be a hurricane, but an extratropical storm.

What’s the difference?

Hurricanes are powered by the release of heat and moisture from warm oceans, says Julian Heming of the Met Office in Exeter, UK. Wind speeds around a hurricane’s core are intense, but fall off relatively quickly further away.

By contrast, storms are driven by the collision of warm and cold air masses. The winds aren’t as extreme as a hurricane, but are strong over a larger area.

Katia will transform from a hurricane to an extratropical storm over the weekend, but forecasts suggest it will remain quite coherent and powerful.

Why is Katia heading for the UK?

Hurricanes form in the tropical Atlantic, and two things have to happen to send them north-east, says Heming.

Each hurricane starts out moving west towards the Americas and is held on that trajectory by a belt of high pressure called the subtropical ridge. So long as the ridge holds strong, the hurricane keeps heading west. But if part of the ridge weakens – for instance, because a low-pressure system collides with it – the hurricane can steer north.

Now over cold water, the hurricane starts losing energy. To keep going, it needs a helping hand from the jet stream, a high-altitude current of fast-moving air. “If the jet stream is strong, it can invigorate the storm and shoot it across the Atlantic very fast,” Heming says.

That’s what has happened to Katia. “We expect it to move very fast,” say Heming, so it will have less time to weaken over the cold ocean.

Do many hurricanes turn east like Katia?

We think of Atlantic hurricanes as mostly affecting the Americas, but many of them do turn east. You can see the tracks of previous hurricanes in this interactive graphic.

The last hurricane to reach the UK was 2009’s hurricane Bill, which was not particularly severe. The last to cause structural damage was hurricane Gordon in 2006, which brought heavy rain and high winds to other parts of western Europe too.

The most recent powerful hurricane to hit the UK was Lili in 1996. Before that, hurricane Charley caused plenty of damage in 1986.

Are the paths of hurricanes changing as the climate warms?

There’s nothing in the weather records to suggest that, Heming says. The paths vary enormously from year to year, so it’s hard to see if there are any long-term trends.

On the other side of the US, models suggest that Pacific hurricanes will shift towards the north central Pacific. As a result, Hawaii may experience more hurricanes in future decades. It’s unclear if similar changes will happen in the Atlantic.

How climate change will affect hurricanes has long been a bone of contention. At the moment it seems there are no more hurricanes than before, and they may actually become slightly rarer. However, hurricanes may also become stronger with climate change.

Is this what caused the “great storm” of 1987?

On 15 October 1987, the UK was famously caught unawares by a major storm that killed 18 people and caused widespread damage. It wasn’t an ex-hurricane like Katia: the storm formed over the bay of Biscay and hit the UK within hours, so it was much harder to predict.