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In-Depth

Hurricanes typically last from two to fourteen days. They tend to move from east to west, at speeds between 10 and 30 mph. Their intensity is ranked on a scale of 1 to 5 called the Saffir-Simpson scale. This scale measures three types of activity: wind speed, air pressure, and storm surge. The storm surge is a 50 to 100-mile-wide dome of water that sweeps across the coastline near where a hurricane makes landfall.

You can see tropical cyclones in satellite pictures of clouds taken from above the earth. But scientists still track tropical cyclones by using airplanes. Only airplanes flying through the storm can tell how big the storm is, how fast it is moving, and how strong its winds are.

How do they determine the "category"?
Category 3, 4, and 5 hurricanes are collectively referred to as intense or major hurricanes. These intense hurricanes cause over 70% of the damage in the United States, even though they account for only 20% of all hurricane strikes. Check the chart below to see how scientists rate hurricanes

Saffir-Simpson Category	Maximum sustained wind speed (mph)	Minimum surface pressure (mb)	Storm surge (feet)
1	74–95 mph	980mb	3–5 ft
2	96–110	979–965	6–8
3	111–130	964–945	9–12
4	131–155	944–920	13–18
5	> 155	< 920	> 18

How do they name the hurricane?
Every tropical cyclone is given a name when it becomes strong and dangerous. The storm name is always used in all weather warnings. Using a name helps people tell one storm from another and follow its movements.

Official storm trackers all over the world have lists of names ready. The chosen hurricane names are used in a 6-year rotation, unless they're retired.

See the official list of names from the National Hurricane Center: http://www.nhc.noaa.gov/aboutnames.shtml

Once the 21 names chosen each year have been used, the Greek alphabet is used to name the storms.

"Retired" Names
Do you share a name with a famous historical hurricane?

Hurricane names are removed from the lists after they've been used for a storm that was very strong or caused a lot of damage.

These names won't be used again:

• Agnes, 1972; Alicia, 1983; Allen, 1980; Andrew, 1992; Anita, 1977; Audrey, 1957
• Betsy, 1965; Beulah, 1967; Bob, 1991
• Camille, 1969; Carla, 1961; Carmen, 1974; Carol, 1965; Celia, 1970; Cleo, 1964; Connie, 1955
• David, 1979; Diana, 1990; Diane, 1955; Donna, 1960; Dora, 1964
• Edna, 1968; Elena, 1985; Eloise, 1975
• Fifi, 1974; Flora, 1963; Fran, 1996; Frederic, 1979
• Georges, 1998; Gilbert, 1988; Gloria, 1985; Gracie, 1959
• Hattie, 1961; Hazel, 1954; Hilda, 1964; Hortense, 1996; Hugo, 1989
• Inez, 1966; Ione, 1955
• Janet, 1955; Joan, 1988
• Klaus, 1990
• Luis, 1995
• Marilyn, 1995; Mitch, 1998
• Opal, 1995
• Roxanne, 1995

Winds inside the storm change speed very quickly. To measure the strength, the National Hurricane Center averages all the wind speeds measured in one minute.

Why do they stop?
Hurricanes derive their energy from the water vapor that evaporates from warm ocean water. Therefore, when a hurricane moves over cold water or over land where it gets cut off from its energy source, it will die.

Some years there are many hurricanes and some years there are very few. Wind and rain patterns from all over the globe affect the number of hurricanes in a year.

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