Tornadoes and Hurricanes Help

Hurricanes

A hurricane can exist for as much as 2–3 weeks. It begins as a series of thunderstorms over tropical ocean waters. Ocean temperature (>26.5°C) and atmospheric pressure serve as a hurricane’s fuel source. The first phase, barometric pressure drop, is called a tropical depression .

High humidity in the lower and middle troposphere is also needed for hurricane development. High humidity slows cloud evaporation and boosts heat release through greater rainfall. Storm intensification to a tropical storm marks the second phase.

Vertical wind shear is also a factor in a hurricane’s development. When wind shear is weak, a hurricane grows vertically and condensation heat is released into the air directly above the storm. This causes even greater buildup.

Wind shear describes the sudden change in the wind’s direction or speed with increasing altitude.

Atmospheric pressure and wind speeds change across the diameter of a hurricane. Barometric pressure falls more and more quickly as the wind speed increases. When winds reach 62–80 knots, a storm is officially a hurricane.

Probably the one feature of a hurricane that most people look for on a weather map is the eye of the hurricane . The eye, roughly 20–50km across, is found in the hurricane’s center with calm or very light winds.

The eye of the hurricane, the central point around which the rest of the storm rotates, is where the storm’s lowest barometric pressures are found.

Just outside of the hurricane eye is the eye wall . This is the place where the most intense winds and rainfall are found. Wind and pressure values inside a hurricane are the same on both sides. Remember the winds are circling all the time.

Hurricane winds turn counter-clockwise about their centers in the Northern Hemisphere and clockwise in the Southern Hemisphere. Figure 14-4 shows the circular wind motion that signals a hurricane.

Fig. 14-4. Hurricanes have strong, rotating vertical cloud masses.

Hurricanes create dangerous winds, torrential rains, storm surges, flooding, riptides, and tornadoes that often result in huge amounts of property damage, deaths, and injuries in coastal locations. In 1992, Hurricane Andrew, the third strongest hurricane to ever hit the United States mainland, came ashore in Florida. It was responsible for at least 50 deaths and more than $30 billion in property damage. Table 14-5 lists the different hurricanes force categories.

Table 14-5 Hurricanes are rated according to specific strength categories.

Severe storms are known by different names in the different parts of the world. The name hurricane is used in the Atlantic and eastern Pacific Oceans, typhoon in the Northwestern Pacific Ocean and Philippines and cyclone in the Indian and South Pacific Oceans.

Since 1953, the Tropical Prediction Center has created yearly lists of hurricanes’ names. As a tropical depression turns into a tropical storm, it is given the next name on the list. In alphabetical order, the names are both male and female. The name of a really destructive hurricane is never used again. Hurricanes Alicia, Andrew, Betsy, Camille, Carmen, Gilbert, Hugo, and Roxanne, to name a few, have been withdrawn from use.

Weather prediction is much more sophisticated than it was 100 years ago. Now, there is time to determine a hurricane’s strength, issue warnings and list evacuation routes.

Practice problems of this concept can be found at: Atmosphere Practice Test