Tropical Cyclone and Scale Hurricane Structure

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At the end of this lesson students should be able to:

• Define the term “hurricane”

• List three categories of a hurricane.

• Tell how a hurricane is formed

• State how a hurricane is measured and name a scale which is used.

• Define the structure of a hurricane

• Explain the effects and impacts on the environment and the society.


A Hurricane is a severe storm with a violent wind. A hurricane is a type of tropical cyclone, the general term for all circulating weather systems counter clockwise in the Northern Hemisphere over tropical waters. When a hurricane is formed over the western Pacific, these hurricanes are called “typhoons,” and similar storms in the Indian Ocean are called “cyclones”.

There are three classifications of Tropical cyclones:

Tropical Depression – is an organized system of thunderstorms with sustained winds of 38 mph.

Tropical Storm – is an organized system of strong thunderstorms with sustained winds of 39 to 73 mph (34-63 knots).  

Hurricane – is an intense tropical weather system with sustained winds of 74 mph (64 knots) or higher.

Hurricanes are products of the Tropical Ocean and atmosphere. Hurricanes are powered by heat from the sea; they are steered by easterly winds and the westerly temperate as well as their own ferocious energy. Hurricanes are formed in the tropical regions. They form there because they need warm water of at least 80º Fahrenheit. They also need high humidity with moist air, light winds, and very warm surface temperatures to succeed. Around their core, winds grow with great velocity, generating violent seas. While moving ashore, they sweep the ocean inward while generating tornadoes and producing torrential rains and floods. The first sign of a hurricane is a cluster of thunderstorms over tropical oceans. After the clusters of thunderstorms arrive they will break away and become better organized. It can take anywhere from hours to several days for a thunderstorm to actually turn into a hurricane. Three things must happen for a hurricane to form. A continuous evaporation and condensation cycle must take place, patterns of winds that are characterized by the converging winds, and a difference in air pressure between the surface and high altitude. Surfaces pressures begin to decrease as water vapour condenses and releases latent heat into areas where the tropical disturbance is located. This latent heat causes the air to become less dense. The warm air then rises; as it rises it becomes cooler and expands. That triggers more condensation and releases more latent heat, which allows more air to rise. A chain reaction is now in place. The exchange of the heat from the surface creates a pattern of wind that moves around the centre. Each year on average, ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. However, five of these will go inland, of these five; two will become major hurricanes ranging Category 3 or greater. In preparing for the hurricane season, the first step is to understand the watches and warnings that are issued by the meteorological department of Jamaica A Hurricane Watch is issued when there is a threat of hurricane conditions to affect land within 48 hours. A Hurricane Warning is issued when hurricane conditions are expected inland 36 hours or less. Hurricane conditions include winds of 74 miles an hour (64 knots) and/or dangerously high tides and waves.

How is a hurricane measured?
Hurricanes are measured using various tools one such tool is the Saffir-Simpson scale. This is a standard scale for rating the severity of hurricanes as a measure of the damage they cause. This scale was first developed in the late 1960s by Herbert Saffir it was made to...
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