Tropical storms 101

What’s the difference between a cyclone, a hurricane, and a typhoon? How do they form? Global News Online takes a closer look at tropical storms.

BASICS

Hurricanes are large swirling storms that form over ocean water, but can travel over land. They bring heavy winds and a large wall of water, called a storm surge, when they hit land. Hurricanes form in the Atlantic Ocean, the Caribbean and eastern Pacific Ocean. (Australians, by the way, refer to hurricanes as "willy-willys.")

Typhoons originate in the western Pacific Ocean. However, typhoon’s winds are generally stronger than a hurricane’s, because of the western Pacific’s warmer water which makes for better storm development. The word typhoon comes from the Chinese term "tai-foong," which means great wind.

Both hurricanes and typhoons are categorized according to wind speed using the Saffir-Simpson Hurricane scale:

Category 1: Winds 119-153 km/hr (faster than a cheetah).

Category 2: Winds 154-177 km/hr (as fast or faster than a baseball pitcher’s fastball).

Category 3: Winds 178-209 km/hr (similar to the serving speed of many professional tennis players). This is also referred to as a "major hurricane."

Category 4: Winds 210-249 km/hr (faster than the world’s fastest rollercoaster). Expect devastating damage by dangerous winds. This can also be called a "super-typhoon" or "major hurricane."

Category 5: Winds more than 259 km/hr (similar to the speed of some high-speed trains). Expect winds to cause catastrophic damage. This can also be called a "super-typhoon" or "major hurricane."

Some experts define hurricanes and typhoons as cyclones, or circular wind storms. But others will argue cyclones are storms in the southern Pacific, generated west of 160 degrees east longitude.

Cyclones are also categorized according to wind speed:

Category 1: Winds less than 125 km/hr. This usually causes "negligible" damage to houses, and may damage some crops, trees and caravans; water craft may drag mooings.

Category 2: Winds 125-170 km/hr. This will cause minor house damage, but significant damage to signs, trees and caravans, and heavy damage to some crops. There may be electrical power failure and small craft my break moorings.

Category 3: Winds 170-225 km/hr. This will cause roof and structural damage, destroy portable buildings, and knock out power.

Category 4: Winds 225-280 km/hr. This will cause significant roofing loss and structural damage, dangerous airborne debris, and widespread power failure.

Category 5: Winds more than 280 km/hr. This will be extremely dangerous and cause widespread destruction. This may also be referred to as a "super-typhoon."

SECTIONS

These storms are comprised of different parts. At the centre is the "eye," which looks like a hole from earth orbit. In the eye of the storm, winds are calm and skies are even clear at times.

Just along the eye of the storm is a band of thunderstorms called the "eye wall," the most violent section of the hurricane.

Extending from the eye wall are "rain bands," spiral arms of precipitation and cloud which can spread over hundreds of kilometres and sometimes contain tornadoes.

HOW THEY FORM

Scientists still have a lot to learn about how these storms form, but there are certain ingredients that are necessary: warm water (typically 26 degrees Celsius or higher) mixed with rising winds that move in one direction.

Hurricanes and typhoons start as tropical disturbances where rain clouds build over warm water. This can become a tropical depression, consisting of rotating thunderstorms and winds of less than 62 km/hr. Heavier winds will elevate the storm to a tropical storm, or a hurricane if the winds top 119 km/hr.

Hurricanes and typhoons can last anywhere from three to 14 days, and longer-lasting storms have been known to travel over 6,000 kilometres.

Most cyclones last three to seven days, but some can last for weeks if the environment allows for it.

Most Pacific storms do not make landfall, at least in North America, making Canada’s west coast relatively safe from hurricanes. But Canada’s east coast lies along the track followed by many Atlantic storms.