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Tropical Weather Information

Each summer and fall, the warm waters of the tropical Atlantic Ocean give birth to tropical storms and hurricanes. Spanning hundreds of miles across with destructive winds, flooding rains and tremendous waves, these are some of the most powerful storms on Earth.

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Formation

Hurricanes need a few conditions to come together in order for a storm to form. First, some pre-existing disturbance in the atmosphere must exist. This could be an area of low pressure along a front, or a tropical wave coming off of the west coast of Africa.

These disturbances need to be located over warm waters of at least 80°F in order to potentially develop. The warm ocean water provided an energy source for the storm. As the water evaporates and rises, it condenses into clouds and, eventually, falls back to the ocean as rain. When this happens, massive amounts of heat are released into the atmosphere. Since warm air is more dense than cool air, this massive release of heat causes the air to sink. Sinking air, in turn, causes the air pressure to drop, strengthening the low pressure system. The stronger the low, the faster the storm will begin to spin.

This happens dozens, if not hundreds of times each season. Yet, we only see a handful of tropical storms and hurricanes each year. There are two main weather phenomenon that are responsible for destroying many of these systems before than can properly organize.

Satellite view of Hurricane Igor in 2010
A satellite view of Hurricane Igor in September 2010.
Wind sheer is generally defined as the change in wind speed and direction over a distance. If wind speed is high, that is, if the winds are changing rapidly either with height, or over the area of the storm, a storm literally gets ripped apart. The atmospheric winds disrupt the circulation of the low pressure, preventing the storm from strengthening at all. If the atmospheric winds are light and constant, a storm will not be disrupted and can strengthen rapidly.

The other detrimental factor that can disrupt development is the presence of dry air. If the atmosphere is very dry in the area of the developing storm, the evaporated ocean water will not be able to condense into clouds and fall as rain. Without these clouds, no heat is released to the atmosphere, and the entire cycle breaks down.

In summary, if some sort of disturbance is located over ocean waters of at least 80°F and is in the presence of light, uniform winds and a moist environment, conditions are favorable for the storm to intensify.

Dangers of Hurricanes

Hurricanes and Tropical Storms present a variety of serious threats to life and property, both at sea and on land.

Saffir-Simpson
Scale of Hurricane Strength
< 38mph: Tropical Depression
39-73mph: Tropical Storm
74-95mph: Category 1 Hurricane
96-110mph: Category 2
111-129mph: Category 3
130-156mph: Category 4
> 157mph Category 5
Winds- Tropical Storms and Hurricanes are classified by their wind speeds using the Saffir-Simpson Scale (pictured at right). It is important to note that the strongest winds surround the very center of the storm, with winds gradually weakening outward from the center. Some of the strongest hurricanes have had winds speeds over 150mph, flattening nearly everything it its path.

Storm Surge- Perhaps the most dangerous part of a hurricane, however, is the storm surge. The storm surge is a rush of water onto land as a tropical system interacts with land. The force of the wind on the water literally pushes the ocean forward. As the ocean becomes more shallow, and turns to land, this wall of water is pushed up along the ground. the result is a rapid rising of the level of the ocean, flooding coastal areas in water that is sometimes feet deep. The quickness of the ocean rise often catches people off guard, trapping them in the flood.

View of the Binghamton Flood in 2010.
Flooding in Binghamton, September 2011 (courtesy NYDMNA)
Rainfall- Tropical systems can continually dump heavy rain for hours or even days. Rainfall totals can easily reach a foot or more. In mountainous areas, especially in the Caribbean and Central America, this can lead to devastating mud slides. More locally, in Central New York, some of our largest floods have been the result of tropical systems, including the Flood of 2011.

Tornadoes- Some land-falling tropical systems are prolific tornado producers, while others produce few if any tornadoes. This is an area of ongoing research in the meteorological research community. Most tornadoes in hurricanes are relatively weak and short lived. That being said, when facing a hurricane, does anyone really want to worry about tornadoes, too?

If you have any questions regarding hurricanes or tropical storms, feel free to contact me!

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