Severe Weather: How Ocean Storms Work, Part 2

BOB DOUGHTY:The National Hurricane Center in Miami, Florida, keeps watch on severe storms. It works closely with public officials and with radio and television stations to keep people informed. Experts believe this early warning system has helped reduce deaths from ocean storms in recent years. But sometimes people cannot or will not flee the path of a storm. That is what happened in many places in New Orleans. BARBARA KLEIN: Weather scientists use computer programs to create models that show where a storm might go. The programs combine information such as temperatures, wind speed, atmospheric pressure and the amount of water in the atmosphere. Scientists collect the information with satellites, weather balloons and devices floating in the world's oceans. They also collect information from ships and passenger flights and from government planes. These planes fly into and around storms. The crews drop instruments attached to parachutes. The instruments report temperature, pressure, wind speed and other conditions. BOB DOUGHTY:Scientists use the Saffir-Simpson Hurricane Scale to measure the intensity of storms based on wind speed. It provides an idea of the amount of coastal flooding and property damage that might be expected. The scale is divided into five groups or categories. The mildest hurricane is called category one. It has winds of about one hundred twenty to one hundred fifty kilometers an hour. This storm can damage trees and lightweight structures. It can also cause flooding. Wind speeds in a category two hurricane can reach close to one hundred eighty kilometers an hour. These storms are often powerful enough to break windows or blow the roofs off houses. Winds between about one hundred eighty and two hundred fifty kilometers an hour represent categories three and four. An even more powerful storm is a category five hurricane. BARBARA KLEIN: The National Oceanic and Atmospheric Administration said Hurricane Katrina was a strong category three hurricane when it hit land in Louisiana. But researchers say other forces than its wind speed helped cause Katrina's extensive destruction. NOAA scientists say Katrina's air pressure was very low. The lower the air pressure, the stronger the storm. And Katrina was also an unusually wide storm. Katrina's most damaging power, however, came from the water it brought. The storm surge was estimated at more than six meters, and may have been as high as nine meters. BOB DOUGHTY:All this water poured into Lake Pontchartrain on the north side of New Orleans. It also flooded into the Mississippi River to the south. New Orleans was built below sea level. The city is surrounded by levees made of earth and walls made of concrete. The water and wind pressure from Katrina broke through the flood dams and destroyed many areas of New Orleans. The surge washed away large areas of the coastal cities of Biloxi and Gulfport, Mississippi. There was also heavy damage in Alabama. BARBARA KLEIN: Some scientists believe climate change affects major storms. Some say the warming of Earth's atmosphere is already making the storms worse. Other scientists have published studies that disagree. Earlier this year, a special World Meteorological Organization committee reported on severe storms. The committee's work appeared in the journal Nature Geoscience. Ten scientists took part. The experts represented both sides of the debate about global warming. They reached no clear answer about whether global warming had already intensified storms. Still, the committee made some predictions. BOB DOUGHTY:They said global warming might cause more powerful ocean storms in the future. They said the overall strength of storms measured by wind speed might increase two to eleven percent by the year twenty-one hundred. And there might be an increase in the number of the most severe storms. But there might be fewer weak and moderate storms. The current Atlantic Ocean hurricane season began in June. Weather experts say fewer severe storms than usual have struck since then. Experts had predicted above-normal numbers of storms during the season, which continues through November. BARBARA KLEIN: This SCIENCE IN THE NEWS was written by Jerilyn Watson. It was produced by June Simms. You can read scripts and download audio at voaspecialenglish.com. You can also find us on Facebook, Twitter, YouTube and iTunes at VOA Learning English. I'm Barbara Klein. BOB DOUGHTY:And I'm Bob Doughty. Listen again next week for more news about science in Special English on the Voice of America. Source: Voice of America