Figure 1. The storm tracks of all the tropical cyclones formed from 1985 to 2005. www.wikipedia.org Vallana Hill, Contributor
June 1 to November 30, commonly referred to as hurricane season, is a critical time for many countries on the Western Hemisphere, especially those in the Caribbean, central and south-east American states.
A hurricane is the common name for a tropical cyclone - a meteorological term used for low-pressure systems characterised by an eye and thunderstorm with strong winds that develop in the tropics.
A tropical cyclone feeds on the heat released when moist air rises and the water vapour it contains condenses. The adjective 'tropical' refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe while the noun 'cyclone' refers to such storms' cyclonic nature, with counterclockwise rotation in the northern hemisphere and clockwise rotation in the southern hemisphere.
Most Atlantic hurricanes begin off the west coast of Africa, starting as thunderstorms that move out over the warm, tropical ocean waters, travelling across the route of the eastern trade winds, towards the Caribbean Sea and its lining countries. A thunderstorm reaches hurricane status in three stages:
Tropical depression - swirling clouds and rain with wind speeds of less than 38 mph (61.15 kph/33 kt)
Tropical storm - wind speeds of 39 to 73 mph (54.7 to 117.5 kph/34 to 63 kt).
Hurricane - wind speeds greater than 74 mph (119 kph/64 kt).
Hurricanes only form over really warm ocean water of 80 degrees F or warmer. The atmosphere (the air) must cool off very quickly the higher you go. Also, the wind must be blowing in the same direction and at the same speed to force air upward from the ocean surface. Winds flow outward above the storm allowing the air below to rise. Hurricanes typically form between five to 15 degrees latitude north and south of the equator.
Although the appearance of a hurricane system may seem two dimensional of wind swirling in a circular motion, there is an entire system of complex processes, between the earth's surface and the lateral clouds.
Latent heat
Warm, moist air from the ocean surface begins to rise rapidly. As this warm air rises, its water vapour condenses to form storm clouds and droplets of rain. The condensation releases heat called latent heat of condensation. This latent heat warms the cool air aloft, thereby causing it to rise.
This rising air is replaced by more warm, humid air from the ocean below. This cycle continues, drawing more warm, moist air into the developing storm and continuously moving heat from the surface to the atmosphere. This exchange of heat from the surface creates a pattern of wind that circulates around a centre. This circulation is similar to that of water going down a drain.
While most persons only identify parts of the hurricane as the eye, the eye wall and the spiral bands, there are three dimensional layers to the system as well.
In the eye, or chimney, the pressure drops rapidly and the temperature rises at even a steeper rate. That is the chimney or eye of the hurricane. A temperature and pressure graph is shown to the right. The low pressure chimney pulls in warm moist air from hundreds of miles around the hurricane to fuel the hurricane.
The warm moist air is carried thousands of feet up the chimney where it is spewed out in cold dry air to form clouds of moisture. Round and round, and up and down the transfer of energy perpetuates the cyclone generator. A visible eye usually forms when winds reach about 80 mph.
Most are familiar with a whirlwind, but the huge size of a hurricane disguises the whirling appearance except when viewed from above. Larger hurricanes extend to a diameter of 100 miles of hurricane force winds. Gale force winds (over 40 mph) can extend over a diameter of 400 miles.
The hurricane like most natural disasters will wreak havoc on entire countries in a little more then a few hours, and while regarded with fear, should also be looked at with awe, for its complexity and sheer power.
References: http://en.wikipedia.org/wiki/Hurricane
www.keyshistory.org
www.howstuffworks.org
The traditional view of parts of a hurricane - Hurricane Katrina - www.katrina.noaa.gov
There is no difference between a hurricane and a typhoon. Hurricane is a term used for a tropical cyclone originating in the Atlantic Ocean or Caribbean Sea, while typhoons originate in the Western Pacific or Indian Oceans.
The three-dimensional cross-section of a hurricane.
The five steps and conditions in the formationof a hurricane.
The term HURRICANE comes from the Spanish origin: 'hurracan' - a Carib word signifying a high wind.
