Giant spinning storms
A hurricane is one of the most powerful storms on Earth. It’s a huge, spinning storm that can be 500 km or more across, with winds above 119 km/h, torrential rain and dangerous flooding.
Hurricanes go by different names around the world, but they’re all tropical cyclones:
| Name | Where |
|---|---|
| Hurricane | Atlantic Ocean and eastern Pacific |
| Typhoon | Northwest Pacific (near Japan, the Philippines) |
| Cyclone | Indian Ocean and South Pacific |
How hurricanes form
Hurricanes need several ingredients:
- Warm ocean water of at least about 26.5 °C, to a depth of about 50 m. This is the storm’s fuel.
- Moist air rising from the ocean.
- Light winds high in the atmosphere, so the storm isn’t torn apart.
- Distance from the equator of at least about 500 km, so the Coriolis effect can make it spin.
The life of a hurricane
| Stage | Wind speed |
|---|---|
| Tropical disturbance | A cluster of thunderstorms |
| Tropical depression | Up to 62 km/h; begins to rotate |
| Tropical storm | 63–118 km/h; given a name |
| Hurricane | 119 km/h or more |
As warm, moist air rises, water vapour condenses and releases heat. That heat warms the air, making it rise even faster, which pulls in more moist air. The storm feeds itself as long as it’s over warm water.
Parts of a hurricane
| Part | Description |
|---|---|
| Eye | The calm centre, 20–60 km across, with light winds and sometimes clear skies |
| Eyewall | A ring of towering thunderstorms around the eye with the strongest winds and heaviest rain |
| Rainbands | Spiralling bands of thunderstorms extending outward |
In the Northern Hemisphere, hurricanes spin counterclockwise.
If the eye passes over you, the storm suddenly goes calm. But it’s not over. The other side of the eyewall arrives soon, with winds blowing the opposite way.
The Saffir–Simpson scale
The Saffir–Simpson scale rates hurricanes by sustained wind speed.
| Category | Winds (km/h) | Damage |
|---|---|---|
| 1 | 119–153 | Some damage to roofs and trees |
| 2 | 154–177 | Extensive damage |
| 3 | 178–208 | Devastating; "major hurricane" |
| 4 | 209–251 | Catastrophic |
| 5 | 252 or higher | Catastrophic; most buildings destroyed |
Hurricane hazards
| Hazard | Danger |
|---|---|
| Storm surge | Winds push ocean water ashore, raising sea levels several metres. Usually the deadliest hazard. |
| Flooding rain | Can cause floods far inland |
| Strong winds | Destroy buildings, topple trees, throw debris |
| Tornadoes | Often form in the outer rainbands |
| Rip currents | Dangerous currents at beaches, even far from the storm |
Naming hurricanes
Since 1953, the World Meteorological Organization has given Atlantic storms names from rotating lists, alternating male and female names. The names of very destructive storms, like Katrina (2005) and Fiona (2022), are retired.
Hurricanes and Canada
Atlantic Canada sees hurricanes and their remains most years, usually from August to October. As they move north over cooler water, they often become post-tropical storms, but they can still be very strong.
| Storm | Year | Impact |
|---|---|---|
| Hazel | 1954 | Flooded Toronto; 81 deaths |
| Juan | 2003 | Category 2 landfall in Halifax; toppled millions of trees |
| Igor | 2010 | Severe flooding in Newfoundland |
| Fiona | 2022 | One of Canada’s costliest weather events; destroyed homes in Port aux Basques, NL, and damaged PEI and Nova Scotia |
The Canadian Hurricane Centre in Halifax tracks storms that may affect Canada.
Climate change and hurricanes
Scientists expect warming oceans to make hurricanes produce more rain, and that a higher share will reach the strongest categories. Rising sea levels make storm surges more dangerous.
Staying safe
- Follow official warnings and evacuation orders.
- Prepare an emergency kit for at least 72 hours.
- Secure outdoor objects and stay indoors, away from windows.
- Never go outside when the eye passes over.
- Avoid floodwater and fallen power lines.
Common mistakes
- Thinking the storm is over when the eye passes.
- Thinking wind is the deadliest hazard. Storm surge and flooding usually cause more deaths.
- Thinking hurricanes never reach Canada.
Try it yourself
- Track a current or past hurricane on a map using its latitude and longitude every 6 hours.
- Spin water in a large bowl and add food colouring to see how a spinning storm draws in material.
- Make a chart comparing hurricanes, typhoons and cyclones.
Quick recap
- Hurricanes are tropical cyclones with winds of at least 119 km/h.
- They form over warm oceans and are fuelled by heat from condensing water vapour.
- The calm eye is surrounded by the violent eyewall.
- The Saffir–Simpson scale rates hurricanes from 1 to 5.
- Storm surge is often the deadliest hazard; Atlantic Canada is affected regularly.