Hurricane Season

It's hurricane season again which happens every year between June and November in North America.

Hurricanes can be big or small. Some hurricanes can be as big as 1000 kilometres across (about the distance between Halifax and Quebec City), while others are only a few hundred kilometres across. Hurricane Emily, which hit Mexico and many nearby islands in July 2005, was a big hurricane. She destroyed thousands of buildings with winds that reached up to 217 kilometres per hour!

How a Hurricane is Formed

There are several things that must come together for a hurricane to form. First off, hurricanes only form over really warm ocean water of 26.5 degrees Celsius or warmer. That's hot! Ocean water off the coast of Canada never reaches that temperature so hurricanes can not form in these waters. The atmosphere (the air) must cool off very quickly the higher you go – like how it is colder when you go to the top of a mountain. The wind must be blowing in the same direction and at the same speed from the ocean surface right up to 9000 metres above sea level. And a hurricane will not form any closer than 500 kilometres to the equator because the Coriolis force is needed to create the spin in the hurricane and it becomes too weak near the equator.

The Coriolis force is a force that deflects moving objects to one side because of the Earth's rotation. The object is still going straight but the Earth moves underneath it, making it look like it is moving to one side. In the Northern Hemisphere, the Coriolis force deflects objects to the right, so winds spin in a counter clockwise direction around a storm centre.

So, sometimes when all of these conditions come together a hurricane or tropical storm (a weaker form of storm) can form. The warm ocean water warms the air above it. This air rises because it is lighter than the cooler air above. When the parcel of warm air reaches the cooler air above, the water vapour turns into water drops and warms the surrounding air. When the warm air rises, the cool air replaces it and wind is created. The wind will start spinning because of the Coriolis force and a tropical storm or hurricane is formed!

To find out more about hurricanes, where they come from, how they are named and how they die, visit the Canadian Hurricane Centre Kid's Page.

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