HUR­RI­CANES, TY­PHOONS, CY­CLONES: WHAT’S THE DIF­FER­ENCE?

IN THE NORTH AT­LANTIC OCEAN AND NORTH­EAST PA­CIFIC, THEY ARE CALLED HUR­RI­CANES, IN THE NORTH­WEST PA­CIFIC OCEAN, IT IS KNOWN AS A TYPHOON, AND IN THE SOUTH PA­CIFIC AND IN­DIAN OCEAN, CY­CLONE IS THE COR­RECT TERM How are they named? Coun­tries in the re­gions of

Fiji Sun - - Big Story - NAVIN SINGH KHAKDA EN­VI­RON­MENT CORRESPONDENT, BBC WORLD SER­VICE

Hur­ri­cane Florence has hit the east­ern seaboard of the United States.

At the same time, Su­per Typhoon

Mangkhut has hit the Philip­pines. There are spec­tac­u­lar images of both shot from space, and the two weather sys­tems look al­most the same.

So why do we call one a hur­ri­cane and the other a typhoon? And while we’re at it - what ex­actly is a cy­clone?

All trop­i­cal storms

They are all the same thing: trop­i­cal storms. But they are known by dif­fer­ent names in dif­fer­ent lo­ca­tions.

In the North At­lantic Ocean and North­east Pa­cific, they are called hur­ri­canes. But if the same type of dis­tur­bance takes place in the North­west Pa­cific Ocean, it is known as a typhoon.

And in the South Pa­cific and In­dian Ocean, cy­clone is the cor­rect term. A trop­i­cal cy­clone is a generic term used by me­te­o­rol­o­gists.

It means a ro­tat­ing, or­gan­ised sys­tem of clouds and thun­der­storms that orig­i­nates over trop­i­cal or sub­trop­i­cal wa­ters, ac­cord­ing to the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion of the US.

“Once a trop­i­cal cy­clone reaches max­i­mum sus­tained winds of 74mph (119km/h) or higher, it is then clas­si­fied as a hur­ri­cane, typhoon, or trop­i­cal cy­clone, de­pend­ing upon where the storm orig­i­nates in the world.” Hur­ri­canes are cat­e­gorised be­tween 1 to 5 based on their wind speed.

When do they oc­cur?

In the At­lantic, it is hur­ri­cane sea­son be­tween 1 June and 30 Novem­ber. More than 95 per cent of trop­i­cal cy­clone ac­tiv­ity oc­curs dur­ing this pe­riod in this re­gion. Ty­phoons in the North­west Pa­cific Ocean are most com­mon from May to Oc­to­ber, although they can form year­round.

And in the South Pa­cific, it’s cy­clone sea­son be­tween Novem­ber and April.

How are they named?

The World Me­te­o­ro­log­i­cal Or­gan­i­sa­tion, a UN body, main­tains a list to name trop­i­cal cy­clones around the world.

The names of the dead­li­est ones like Typhoon Haiyan or Hur­ri­cane Katrina are re­tired and re­placed. Coun­tries in the re­gions of hur­ri­canes, ty­phoons and cy­clones send sug­ges­tions for the list to the global met au­thor­ity.

“Eight coun­tries in our re­gion, which cov­ers the Bay of Ben­gal and the Ara­bian Sea, sent the list to the WMO dur­ing the early 2000s,” a se­nior sci­en­tist with the In­dian Me­te­o­ro­log­i­cal De­part­ment told the BBC. “Nearly 50 per cent of those names for cy­clones have been ex­hausted. “The agree­ment be­tween the coun­tries in our re­gion then was to make sure that the names do not hurt re­li­gious sen­ti­ment in our coun­tries.”

How are they formed?

Air rises quickly when it is heated by warm sea wa­ter.

As the air cools down again it is pushed aside by more warm air ris­ing be­low it.

This cy­cle causes strong winds. Over the sea, a trop­i­cal storm can whip up huge waves.

When th­ese waves reach land they can flood large ar­eas, in­clud­ing towns and cities.

Over land the strong winds can cause a lot of dam­age - they can flat­ten homes, knock over trees and even tip over cars.

Sci­en­tists say the tem­per­a­ture of ocean wa­ter is go­ing up and that can lead to hur­ri­canes in­creas­ing in in­ten­sity in the fu­ture.

They add that a hot­ter at­mos­phere can also hold more wa­ter, so this should al­low hur­ri­canes to dump more wa­ter on af­fected ar­eas. There are many fac­tors which make the re­la­tion­ship be­tween cli­mate change and hur­ri­canes a com­plex one. Feed­back: jy­otip@fi­jisun.com.fj

Sci­en­tists say the tem­per­a­ture of ocean wa­ter is go­ing up and that can lead to hur­ri­canes in­creas­ing in in­ten­sity in the fu­ture. They add that a hot­ter at­mos­phere can also hold more wa­ter, so this should al­low hur­ri­canes to dump more wa­ter on af­fected ar­eas.

Four named storms were ac­tive in the At­lantic with the other three slam­ming through the Pa­cific.

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