2011 tornado death toll tops 500 and season not over

A car lies half submerged in a swimming pool in the backyard of a home, which is destroyed by a tornado in Joplin, Missouri May 25, 2011.

CHICAGO (Reuters) - More than 500 people have been killed by twisters in 2011, making it the deadliest tornado year in the United States since 1953, according to the National Weather Service.

"And we're not over yet," said meteorologist David Imy of the NOAA Storm Prediction Center on Thursday.

As of mid-Thursday, 505 people had died in tornadoes this year, including at least 123 who died as a direct result of the monster storm that tore through Joplin, Missouri, on Sunday. The official death toll from Joplin is 125 but a couple of those may not have been directly related to the tornado.

The National Weather Service reported another 17 deaths this week in Oklahoma, Kansas and Arkansas. This number also differs slightly from what individual states are reporting.

The total makes 2011 the seventh-deadliest tornado year on record in the U.S. and inches it closer to the 519 deaths recorded in 1953.

This year's tornado death toll ranks as the highest ever through the month of May in the National Oceanic and Atmospheric Administration and National Weather Service's official record, which dates back to 1950.

Most of the fatalities occurred in April, when twisters took 361 lives, records show.

At least 53 tornadoes in Alabama on April 27 killed 238 people in that state alone, weather experts and government officials said.

There have been approximately 1,000 tornadoes in the U.S. so far this year, according to the National Weather Service's preliminary estimate.

Fifteen are confirmed EF-4 and EF-5 tornadoes on the Enhanced Fujita scale and that number is expected to climb, Imy said.

The Joplin tornado was rated an EF-5, with winds topping 200 miles per hour. The only other EF-5 tornadoes this year happened on April 27, with two in Mississippi and one in Alabama, Imy said.

The deadliest tornado year in the U.S. was 1925, when twisters claimed 794 lives. The next deadliest years were as follows: 552 deaths in 1936, 551 in 1917, 540 in 1927, 537 in 1896 and 519 in 1953.

(Reporting by Colleen Jenkins; Additional reporting by Mary Wisniewski; Editing by Greg McCune)