All you need to know about hurricanes!

  • Created by: Lucy
  • Created on: 04-01-12 11:00

What is a hurricane?

A hurricane is a tropical storm with sustained wind speeds in excess of 120km/h which originated in the tropics.


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What is the coriolis effect?

The coriolis effect is the way in which moving obejects are deflected to the right in the northern hemisphere (left in southern hemisphere) by the spin of the earth. This determines the general path of hurricanes and their internal rotation.


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What conditions are necessary in order for a hurri

The coriolis effect is compulsory in order for a hurricane to form and because of this, it must be either 5 degrees north/south of the equator. In addition to this, there must be light wind and a humidity of at least 75%. It must be over warm water of at least 26 degrees celsius and there must be a storm.

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Why can't hurricanes form over the equator?

The coriolis effect is NEEDED for a hurricane form, and this is not present over the equator, so a hurricane cannot possibly form there.

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The Saffir-Simpson Scale

The Saffir-Simpson scale is used to measure hurricanes. There are 5 categories, with 1 being the least damaging, and 5 being the most damaging.

Level 1 hurricane conditions - wind speeds of up to 95mph, 1-2m sea-level rise, some flooding, damage to trees and mobile homes.

Level  3 hurricane conditions - wind speeds of up to 130mph, 4m sea-level rise, damage to small buildings, house flooding, trees knocked down.

Level 5 hurricane conditions - wind speeds of up to 155mph, 18ft sea-level rise, flooding, trees blown down, building damage.

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Case Study: Hurricane Irene

What? - Hurricane Irene was a category 3 hurricane which formed on 20th August, 2011 and dissipated on 29th August, 2011. Many areas were affected by the hurricane, which was part of the 2011 Atlantic hurricane season.

Where? - The main affected areas where: Lesser Antilles, Greater Antilles, Turks and Caicos, the Bahamas, eastern Canada and eastern United States (landfalls in North Carolina, Connecticut, New Jersey and New York).

Effects? - Hurricane Irene resulted in extensive flooding and wind damage. Also, there was significant property damage and there was a total of 55 fatalities. There was a staggering $10.1bn worth of damage in the U.S. and monetary losses in the Caribbean was approximately US$3.1bn.

Why? - Hurricanes form when warm, moist air over the ocean rises from the near surface. This creates an area of low air pressure below. Higher pressured air from the surrounding area pushes into the low pressure area and also becomes warm and moist, before rising too. As the warm air continues to rise, the surrounding air swirls in to take its place.

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Case Study: Hurricane Irene (continued)

When the warm, moist air rises and cools, the water in the air forms clouds. This system of clouds and wind, spins and grows. This is fed by the ocean's heat and water evaporating from the surface. As the storm rotates faster and faster, an eye forms in the centre. Here, it is calm and clear with low pressure. Higher air pressure from above flows into the eye. When wind speeds reach 74mph, the storm is officially a hurricane. They usually weaken when they hit land because they are no longer being "fed" by the warmth of the ocean. Before dying out completely, they often move further inland dumping inches of rain and causing major wind damage.

The effects of Hurricane Irene have impacted many people. These include those whose homes have been damaged, those who had to leave their home for their own safety, those who lost a friend/family member, those who run safety shelters and business owners.

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Best defintion of the coriolis effect!

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