Hurricane season: Record number of named Atlantic storms

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Tropical storm Eta in FloridaImage source, EPA
Image caption,
Florida was struck by a tropical storm at the weekend

This year's Atlantic hurricane season has broken the record for the number of named storms, the US National Hurricane Center says.

Subtropical storm Theta in the north-east Atlantic is the 29th, breaking the previous record of 28 set in 2005.

Forecasters say another system is forming in the Caribbean which could be named in the near future.

Meteorologists say several factors are behind the increasing number of tropical storms.

Particularly dangerous storms are given names to raise public awareness before they strike.

The hurricane season, which runs from 1 July to 30 November, has produced storms like Eta, which struck Florida at the weekend after causing destruction and killing dozens in parts of Central America.

Zeta hit Louisiana at the end of October, becoming the fifth named storm to make landfall in the state this season.

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Theta, not currently a hurricane, is moving north-eastwards towards southern Europe.

Forecasters are watching the formation of another possible storm moving westwards over the central Caribbean Sea.

Why has 2020 been so active?

There are a number of factors which have contributed to a very active hurricane season, says BBC meteorologist Nikki Berry.

The most influential are very warm sea surface temperatures, low wind shear, increased instability over West Africa and La Nina, she adds.

Sea surface temperatures were consistently 1-2C above normal through the summer months and these anomalies increased to 2-3C during September, especially around the Caribbean, Gulf of Mexico and off the coast of Africa, where many storms start to develop.

Wind shear was extremely low through the summer months and this allows tropical storms to intensify and maintain tropical circulations, rather than being torn apart by opposing winds in the different layers of the atmosphere.

A pulse of enhanced rainfall, known as the Madden-Julian Oscillation, moves eastwards round the equator - when it is located over West Africa, it causes more rainfall and thunderstorms which can give birth to tropical storms over the east Atlantic.

La Niña, a change in Pacific Ocean temperatures with cooler water being pushed eastwards across the equatorial Pacific, has also been more influential. It can affect global weather patterns and one of the effects is an increased number and strength of Atlantic tropical cyclones, especially late in the season.

What about climate change?

While the hurricane season this year has been very active, there is conflicting evidence over whether such storms are becoming more frequent.

However, scientists expect climate change to make these storms stronger. Hurricanes are powered by warm seas and warmer air means that storms can dump more water on land, increasing their destructive power.

This season is also the first since 2005 during which the 21 alphabetical names set by the World Meteorological Organisation (WMO) have run out because of the number of storms. The WMO began using Greek names in September.

Media caption,
Storms Theta and Eta update


A guide to the world's deadliest storms

Hurricanes are violent storms that can bring devastation to coastal areas, threatening lives, homes and businesses.

Hurricanes develop from thunderstorms, fuelled by warm, moist air as they cross sub-tropical waters.
Warm air rises into the storm.

Air swirls in to fill the low pressure in the storm, sucking air in and upwards, reinforcing the low pressure.

The storm rotates due to the spin of the earth and energy from the warm ocean increases wind speeds as it builds.

When winds reach 119km/h (74mph), it is known as a hurricane - in the Atlantic and Eastern Pacific - or a typhoon in the Western Pacific.

"Everybody has a plan until they get punched in the face. Well, we're about to get punched in the face."
Florida Mayor Bob Buckhorn, ahead of Hurricane Irma (2017)

The central eye of calmer weather is surrounded by a wall of rainstorms.
This eyewall has the fastest winds below it and violent currents of air rising through it.

A mound of water piles up below the eye which is unleashed as the storm reaches land.
These storm surges can cause more damage from flooding than the winds.

"Urgent warning about the rapid rise of water on the SW FL coast with the passage of #Irma's eye. MOVE AWAY FROM THE WATER!"
Tweet from the National Hurricane Center

The size of hurricanes is mainly measured by the Saffir-Simpson scale - other scales are used in Asia Pacific and Australia.

Winds 119-153km/h
Some minor flooding, little structural damage.
Storm surge +1.2m-1.5m

Winds 154-177km/h
Roofs and trees could be damaged.
Storm surge +1.8m-2.4m

Winds 178-208km/h
Houses suffer damage, severe flooding
Storm surge +2.7m-3.7m

Hurricane Sandy (2012) caused $71bn damage in the Caribbean and New York

Winds 209-251km/h
Some roofs destroyed and major structural damage to houses.
Storm surge +4m-5.5m

Hurricane Ike (2008) hit Caribbean islands and Louisiana and was blamed for at least 195 deaths

Winds 252km/h+
Serious damage to buildings, severe flooding further inland.
Storm surge +5.5m

Hurricane Irma (2017) caused devastation in Caribbean islands, leaving thousands homeless

"For everyone thinking they can ride this storm out, I have news for you: that will be one of the biggest mistakes you can make in your life."
Mayor of New Orleans Ray Nagin ahead of Hurricane Gustav, 2008

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