Washington (AFP)

Hurricane Dorian, which struck northern Bahamas, is one of the worst storms in the history of this Caribbean archipelago. It is also the fifth category 5 hurricane to have formed in the Atlantic in the last four years.

- What is a category 5 hurricane? -

In meteorology, scientists classify hurricanes on a scale of 1 to 5 on the so-called Saffir-Simpson scale, to describe the intensity of storms.

Category 5 hurricanes generate winds greater than 252 kilometers per hour, according to this classification.

In addition to the devastating winds, this type of hurricane can be accompanied by torrential rains and catastrophic rising waters, causing tsunami-like floods when they hit the coast.

Hurricane Dorian's winds approached 300 km / h, an unparalleled level in the history of the Bahamas, according to the National Hurricane Center (NHC).

This type of cyclone is also becoming more frequent: one has been observed each year since 2015, a record series. They were much rarer before.

- Small and big storms -

In 2016, Hurricane Matthew was the first category 5 cyclone to hit the Atlantic since 2007.

Another category 5 hurricane, Irma, devastated the Caribbean and the southern United States in September 2017.

Particularly violent, Hurricane Katrina - also Category 5 - killed more than 1,800 people on the Gulf Coast in 2005.

In comparison, Hurricane Florence in 2018 was downgraded to category 1, before touching the coasts of North Carolina and South Carolina, though it was extremely dangerous.

"An event of lesser category can be dangerous and do great damage," said Emmanuel Bocrie, weather forecaster at Météo-France, interviewed at the time.

Less powerful, however, Florence had poured torrential rains into lands already waterlogged in North Carolina, South Carolina and western Virginia, causing floods and leaving more than 480,000 homes without electricity.

- 2018, deadly year -

In 2018, a series of particularly violent storms, including Hurricane Florence in September and Hurricane Michael a month later, killed dozens of people and caused some $ 32 billion ($ 29 billion) worth of damage. in North Carolina, South Carolina and Florida.

Hurricane Michael is considered the most powerful storm to hit the United States since 1969.

In May, the NOAA Oceanic and Atmospheric Agency predicted for 2019 a "near normal" hurricane season in the Atlantic. But the authorities are encouraging Americans to be ready to deal with these phenomena, as more than 80 million people live in high-risk areas, even if they do not live directly on the coast.

For the inhabitants, the main threat is mainly floods, more than the strong winds.

- The worst coming? -

Scientists have long felt that global warming should make tropical storms even more destructive in the future, a reality already visible, according to some of them.

Increasing ocean temperatures, the main cause of hurricane intensification, and rising sea levels could also undermine coastal defense systems.

© 2019 AFP