Hurricane Irene is sweeping up the eastern Atlantic seaboard. Residents of Ocracoke Island in North Carolina's Outer Banks have been evacuated. Irene is causing concern for everyone, especially children who either remember past hurricanes with fear or have no experience with hurricanes. Here is a Q-and-A to help explain hurricanes to children.
* What is the difference between a tropical depression, a tropical storm and a hurricane?
A tropical depression is collection of thunderstorms with the right characteristics (rain, low pressures, wind speeds) to become a tropical storm. Tropical depressions have steady internal wind speeds of 23-39 mph. At 40-73 mph winds it becomes a tropical storm and gets a name. Hurricanes are tropical storms with sustained wind speeds over 74 mph that begin over oceans. Atlantic Ocean storms are called hurricanes. In the Pacific Ocean, they are called tropical cyclones or typhoons.
* When is hurricane season?
June 1 to November 30 is the official season, but most occur between mid August and early October.
* What does a hurricane's category mean?
Like the Fujita Scale (now Enhanced Fujita) used for tornadoes, hurricanes are rated using the Saffir-Simpson Scale rating of 1-5. Category 5 hurricanes are the most intense. Wind speeds are as follows:
Category 1: 74-95 mph (Charley, 1988)
Category 2: 96-110 mph (Gustav, 2008)
Category 3: 111-130 mph (Alicia, 1983 and Irene, 2011)
Category 4: 131-155 mph (Andrew, 1992)
Category 5: greater than 155 (Katrina, 2005)
* How are hurricanes categorized?
The Saffir-Simpson categorizes hurricanes on wind velocity, danger levels, structural damage and utility loss.
* What does air pressure have to do with hurricanes?
Atmospheric pressure is measured in millibars (mb) and millimeters of mercury (hg). Hurricanes are graded by their air pressure lows. The lower the internal air pressure, the more severe the storm.
* What does "made landfall" mean?
"Landfalls" are the points at which hurricanes touch land. Hurricane wind speed is measured at the times when they make landfall (hit land). Hurricane Camille had the highest wind speed, 190 mph, when she made landfall at Pass Christian, Miss., on August 17, 1969.
* Why do hurricanes change categories change?
Hurricanes follow paths, shift course, intensify and sometimes stop and restart. Katrina began as tropical depression 12, was upgraded to a tropical storm and made first landfall Florida as a Category 1 hurricane. Katrina became a Category 4 and 5 over the Gulf of Mexico, but made her second and third landfalls as a Category 3.
* Which are the worst hurricanes?
There is no definitive answer for worst hurricane, because several factors combine to create them. Here are some record-breaking storms.
--22,000 people died in the Great Hurricane of 1780, the deadliest Atlantic Basin hurricane.
--The Galveston Hurricane of 1900 was the deadliest U.S. hurricane, with 8,000 deaths.
--Hurricane Mitch (1998) set records for highest Atlantic Basin rainfall at 75 inches, longest hurricane at 13 days and deadliest in the western hemisphere. 11,000 people died in Central America.
--Hurricane Wilma (2005) replaced Hurricane Gilbert (1988) as the most powerful storm with pressure lows of 26.05 hg (882 mb) and highest sustained winds of 175 mph.
--Hurricane Katrina (2005) did the most damage (over $100 billion), had the third largest death toll in U.S. history (1,836), the highest storm surge ( 27.5 feet) and highest water mark (34.1 feet). Katrina is differentiated by extensive flooding. Broken levees covered 80 percent of New Orleans with 6-10 feet of water. Areas worst hit were the lower 9th ward, New Orleans East, Gentilly, Lakeview, St. Bernard Parish and Plaquemines Parish.
Marilisa Kinney Sachteleben writes from 22 years parenting four children and 25 years teaching K-8, special needs, adult education, science and homeschool.
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