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13.3 Notes – TOPIC:
Tropical Storms
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Tropical cyclones
 Summer and fall, the tropics experience conditions ideal for the formation of large, rotating, low-pressure tropical
storms
 In different parts of the world they are known as hurricanes, typhoons, and cyclones.
Location
 Tropical storms exist in all tropical oceans except the South Atlantic and the Pacific Ocean west of South America
because these areas contain regions of nearly permanently stable air and cooler water.
 Western Pacific they are known as typhoons.
 Near the Indian Ocean they are called cyclones.
 North Atlantic, the Gulf of Mexico and the Caribbean Sea they are called hurricanes.
Hurricane formation
 Two things are required for the formation of a hurricane:
1. An abundant supply of warm ocean water, and
2. Some sort of lifting mechanism to lift the warm air and keep it rising.
There are 3 stages in the development of a hurricane.
Formative stage
 Less dense moist air is lifted causing rainfall and air circulation.
 The rising air causes an area of low-pressure where warm less dense air moves toward the area of low pressure.
 When the tropical ocean has a disturbance that rotates around a center of low pressure it has reached the
developmental stage and is called a tropical depression with wind speeds of 23-39 mph.
Mature stage
 Moving air approaches the center of the growing storm, rises, rotates, and increases in speed.
 Air pressure in the center will decrease.
 As long as warm air feeds the system at the surface and is removed in the upper atmosphere, the storm will continue
to build.
 When the wind speeds reach 40 mph, the system is called a tropical storm.
 When the wind speeds reach 75 mph, it is called a hurricane.
 The eye of the storm is in the middle with calm, blue skies.
 This is usually 19 to 37 miles wide.
 The strongest winds are in the eyewall.
Dissipation stage
 A hurricane will only last until there is no longer enough energy to sustain itself.
 This happens when it moves over land or into cooler water.
Saffir-Simpson Hurricane Scale
 This scale classifies hurricanes according to wind speed, potential for flooding and potential for property damage.
Storm surge
 Occurs when strong winds drive a mound of water toward coastal areas where it washes over land.