Exceptionally intense NOAA via Getty Images

Hurricane Dorian is setting unwanted records as it devastates the Bahamas en route to Florida. It put on an unprecedented burst of intensification as it moved over water that is abnormally warm due to global warming, and is tied with a 1935 hurricane as the strongest ever to strike land in the Atlantic.

On Sunday, Category 5 Dorian made landfall in Elbow Cay in the Abaco Islands of the northern Bahamas with sustained winds of 300 kilometres an hour (185 mph) and gusts of up to 350 kph (220 mph) – the strongest hurricane ever to hit any island in the Bahamas.

On Monday morning Dorian was moving over Grand Bahama and the city of Freeport. Its sustained wind speeds have dropped to 270 kph (165 mph), but it remains a Category 5 hurricane.


It will be many days before the full extent of the damage becomes clear, but initial reports suggest it will be extreme, with storm surges of several metres in addition to the wind and one death has already been confirmed.

The official forecast suggests Dorian will turn north and move up the coast of Florida, Georgia and the Carolinas without its centre moving over land. It will weaken as it does so, but storm surges, rainwater flooding and wind are still expected to cause extensive damage along the coast.

Hurricane Matthew followed a similar path in 2016 and caused $11 billion in damage.

Weather services were also forced to clarify that Alabama is not in danger after President Trump wrongly claimed it was on Twitter.

There’s no doubt that global warming has made Dorian more damaging. For starters, local sea level is around 0.2 metres higher than normal already, making storm surges that much higher and more damaging.

Unprecedented

In addition, hurricanes are fuelled by warm surface waters. Dorian moved over waters up to 1⁰C warmer than normal. It intensified at an unprecedented rate for an already strong storm, with wind speeds going from 240 to 300 kph in under 9 hours. That has never been observed in the Atlantic before.

Hurricanes are expected to intensify faster, to become stronger overall, to dump more rain and to move more slowly as the world warms, and that seems to be just what is happening.

All these factors make storms far more damaging. For instance, wind damage rises exponentially as wind speeds increase, while slow-moving storms can dump far more rain in one place.

The only stronger hurricane than Dorian ever recorded in the Atlantic was Allen in 1980, whose sustained winds peaked at 305 kph (190 mph). However, its wind speeds were slower by the time it struck land.

Next steps on climate change: Christiana Figueres at New Scientist Live