By Kevin Murphy
KANSAS CITY, Mo (Reuters) - The deadly May 22 tornado in Joplin, Missouri caught many residents unprepared, partly because warnings issued that day were met with complacency and confusion, a federal report said on Tuesday.
"The vast majority of Joplin residents did not immediately take protective action upon receiving a first indication of risk, regardless of the source of the warning," a 40-page study by the National Oceanic and Atmospheric Administration said.
The EF-5 tornado, which hit shortly after 5:30 p.m. on a Sunday, killed 162 people and destroyed some 9,000 homes and other buildings as it tore through central Joplin.
Joplin officials sounded a series of sirens for about 20 minutes as a severe storm system moved in from the west. Meanwhile, the National Weather Service issued tornado warnings, broadcast over the radio, television and other media.
In Joplin, like some other cities, sirens are sounded when a tornado or storms with winds of 75 miles per hour are expected, the report said. They are not necessarily associated directly with a weather service warning, it said.
In interviews with nearly 100 survivors of the tornado, NOAA officials found that the perceived frequency of warning sirens that night and in previous storms caused people to become "desensitized or complacent to sirens" and to not take shelter.
"Instead, the majority of Joplin residents did not take protective action until processing additional credible confirmation of the threat," the report said. For example, people would see the darkening sky or turn on a television or radio to confirm the urgency of the situation.
The report recommends the weather service work with other agencies to develop a more effective warning system that coordinates sirens with other warning methods. The system should be easily understood by the public, the report recommends.
For instance, a non-routine warning is recommended to prompt people to take "immediate, life-saving action" when tornado or extremely severe weather is imminent.
The report recommends that current GPS technology and NOAA Weather Alerts be better employed.
"While the weather enterprise was generally successful in communicating the Joplin tornado threat in a timely manner, current communication and delivery mechanisms are not seamless and are somewhat antiquated," the report said.
NOAA said it was unclear how many lives could have been saved on May 22 if more people heeded warnings and took shelter more quickly. Fortunately, the tornado moved rather slowly, which assisted people who did respond to sirens and other warnings, the report said.
(Reporting and writing by Kevin Murphy; Editing by Mary Wisniewski and Cynthia Johnston)