The vicious circle: Your questions about cyclones answered

What's the difference between a cyclone and a hurricane and six other things you should know as Cyclone Ashobaa heads our way

Tropical Cyclone Ingrid approaches Cape York Peninsula, Australia on March 7, 2005. Tropical cyclones only form over oceans where the surface temperature has reached at least 26.5°C NASA / GSFC/ Getty Images
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As Cyclone Ashobaa winds through the Arabian sea, expected to make landfall in Oman, The National explores the violent phenomenon.

What is the difference between a cyclone, hurricane and typhoon?

Cyclone, hurricane or typhoon? When it is barrelling down on you at the speed of a fast-moving car and with waves the size of a house, does its name really matter?

The answer is that these are nothing more than three different names for the same phenomenon – a weather disturbance fuelled by moisture and warm oceans to produce high winds, torrential rain and massive waves.

In the Atlantic Ocean and the north-east Pacific, such storms are called hurricanes. The name is generally accepted to come from Hurican, the god of evil of the Caribbean Indians. Hurricane season in the Atlantic is generally between June and November.

In the western Pacific, including Japan, China and the Philippines, such storms are known as typhoons, and can occur throughout the year, peaking in August and September.

The origin of the name is unclear, for while it refers to the Greek word for whirlwind “typhon” it may also come from the Chinese “tai fung” meaning “great wind”, and the Arabic “Al-tufan”, which refers to a great flood or storm in the Quran.

The word may have been spread around the world by Portuguese navigators from the 15th century as they sailed east.

Cyclones are recorded in the rest of the Pacific, the Indian Ocean and Arabian Sea. The name is from the Greek “kuloma”, meaning a wheel or a coiled snake.

How do you measure the strength of a cyclone?

Cyclones are measured differently according to whether they are in the northern or southern hemisphere, and in which ocean basin they are formed.

There are six classification systems, each with its own terminology and wind-speed breakdowns.

The strongest tropical cyclone in the north Indian Ocean in the northern hemisphere is measured using the India Meteorological Department Tropical Cyclone Intensity Scale, and is known as a super cyclonic storm with sustained wind speeds of more than 222 kilometres per hour.

Japan’s Regional Specialised Meteorological Centre in Tokyo measures cyclones that develop in the northern hemisphere’s western Pacific. The strongest on its scale is a violent typhoon with sustained winds of more than or equal to 194kph.

How do cyclones form?

Tropical cyclones form only over oceans where the surface temperature has reached at least 26.5°C because they rely on the warm air as fuel to grow in size and strength.

As the warm air rises from the ocean surface, it leaves an area of low pressure underneath. This space is then flooded with air from surrounding areas of higher pressure which, in turn, also heat up and rise.

The effect of this constant rising and filling is a continuous, spinning column of clouds that gets faster as it gets bigger. As the warm, wet air rises, it eventually cools down and forms heavy clouds above the spiral, which can resemble spinning discs.

How rare are cyclones in this part of the world?

Cyclones are unusual in the Arabian Sea, but can occur during the monsoon season, which generally runs from April to December, when the prevailing winds pull moisture towards India. They can, on occasion, impact the Arabian Peninsula.

According to weather records in Pakistan, about 50 tropical cyclones have formed in the Arabian Sea since records began in 1885. But most have made landfall on the coasts of India and Pakistan.

Are cyclones a threat to the UAE?

Since records were first collected in 1945, no cyclone has yet made a direct hit on the UAE. The closest instance was in 2007, when Cyclone Gonu, the strongest storm yet recorded in the northern Indian Ocean, was upgraded to a super cyclonic category 5 storm on June 4, with winds of 240kph. Two days later it crossed the coast of Oman, flooding Muscat, knocking out power and leaving 50 to 60 people dead.

Fujairah was the next to feel the brunt of Gonu, with 10 metre-high waves and heavy rain causing widespread flooding that closed the main road to Kalba and sunk a number of fishing boats. Gonu weakened and moved north, coming ashore at Chabahar in Iran, the first cyclone to hit the country since 1898.

In 1977, the UAE escaped the Oman cyclone, which left 105 people dead, and also the 2002 Oman cyclone, which killed nine in Dhofar after making landfall at Salalah.

What was the deadliest cyclone in history?

The deadliest tropical cyclone on record hit what is now Bangladesh and West Bengal, in India, in 1970.

Cyclone Bhola originated in the central Bay of Bengal in November and gathered speed and strength as it moved north. Its wind speed peaked at 185kph and it hit land in what was then East Pakistan on November 12. Villages and crops were obliterated as the cyclone destroyed everything in its path.

While the cyclone was not the strongest on record, it was the deadliest. Between 300,000 and 500,000 people were thought to have died either at sea or on land, once Cyclone Bhola landed. A weather station up to 100km away registered winds of 144kph before its equipment was blown away.

British newspaper The Guardian reported from Manpura Island in East Pakistan in the aftermath, where it said three-quarters of the 22,000 inhabitants were killed.

“A 90-minute walk through muddy debris, heavy with the stench of death, gave no reasons to doubt the size of the losses estimated by local leaders,” wrote journalist Howard Whitten.

Why Cyclone Ashobaa?

Naming tropical cyclones is thought to make it easier for experts, media and the public to discuss and reference the storm, limiting the chance of errors.

The first list of names for storms in the Atlantic was created in 1953 by the National Hurricane Centre. It included only female names but was updated in 1979 to include men’s names.

The World Meteorological Organisation, which assigns the names, now uses six lists in rotation.

Naming cyclones that form in the north Indian Ocean started much later, in 2004, after long deliberations, according to the India Meteorological Department. Bangladesh, India, the Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand each chose eight names to be used in rotation.

Ashobaa was picked by Sri Lanka. The next cyclone in the area will be called Komen, contributed by Thailand. Cyclone Hudhud, which hit eastern India and Nepal in October, was named by Oman, using the Arabic word for the distinctive-looking hoopoe bird found across the region.

jlangton@thenational.ae

munderwood@thenational.ae

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