Hurricanes

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hurricanes-key

How hurricanes form from the BBC

Hurricanes are giant, spiraling tropical storms that can have wind speeds of over 257 kilometers an hour and unleash more than 9 trillion liters of rain a day. These same tropical storms are known as cyclones in the northern Indian Ocean and Bay of Bengal, and as typhoons in the western Pacific Ocean.

The Atlantic Ocean’s hurricane season peaks from mid-August to late October and averages five to six hurricanes per year.

Hurricanes begin as tropical disturbances in warm ocean waters with surface temperatures of at least 26.5 degrees Celsius. These low pressure systems are fed by energy from the warm seas. If a storm achieves wind speeds of 61 kilometers an hour, it becomes known as a tropical depression. A tropical depression becomes a tropical storm, and is given a name, when its sustained wind speeds top 63 kilometers an hour. When a storm’s sustained wind speeds reach 119 kilometers an hour it becomes a hurricane and earns a category rating of 1 to 5 on the Saffir-Simpson scale.

Hurricanes are enormous heat engines that generate energy on a staggering scale. They draw heat from warm, moist ocean air and release it through condensation of water vapor in thunderstorms.

Hurricanes spin around a low-pressure center known as the “eye.” Sinking air makes this 32- to 48-kilometer-wide area notoriously calm. But the eye is surrounded by a circular “eye wall” that hosts the storm’s strongest winds and rain.

These storms bring destruction ashore in many different ways. When a hurricane makes landfall it often produces a devastating storm surge that can reach 6 meters high and extend nearly 161 kilometers. Ninety percent of all hurricane deaths result from storm surges.

A hurricane’s high winds are also destructive and may spawn tornadoes. Torrential rains cause further damage by causing floods and landslides, which may occur many miles inland.

The best defense against a hurricane is an accurate forecast that gives people time to get out of its way.

What can a hurricane do?

Some basic research – do you agree or disagree and can you say why? Make a copy of this table, and record your verdict on the statement along with your (referenced) evidence. Upload to the dropbox.

 
Hurricanes, tropical cyclones and typhoons are three terms for three different extreme natural events.
Hurricanes are like tornadoes in their spatial extent.
Hurricanes are a very predictable hazard.
Climate change is causing the frequency of hurricanes to increase.
Hurricanes occur on the equator.
A tropical storm is a hurricane when the wind speed reaches 119 km/h.
You can’t out run an approaching hurricane.
The safest place to be during a hurricane in it its eye.

Hurricane Frequency

This graph from the US National Hurricane Center shows the frequency of named storm systems and hurricanes over the last 150 years. TOK SPOT – Can we draw conclusions from this limited data?

hurricane frequency

Bars depict number of named systems (yellow), hurricanes (green), and category 3 or greater (red)

 

Are hurricanes becoming more frequent or more violent? Make notes from this article from The Independent: Global warming is ‘causing more hurricanes’ [16 October 2012] and this National Geographic article ‘Is global warming making hurricanes worse?’

Prediction

Essay question: How predictable are hurricanes? (10 marks)

Case Studies – Katrina and Nargis

BBC – Hurricane in January

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