(Adds background, details)

MIAMI, June 19 (Reuters) - Tropical Storm Chris formed over the open Atlantic Ocean on Tuesday and posed no threat to land, the Miami-based U.S. National Hurricane Center said.

Chris, the third cyclone of 2012 Atlantic hurricane season, swirled to life 560 miles (905 km) south-southwest of Cape Race, Newfoundland, and had top sustained winds of 45 miles (75 km) per hour, the hurricane center said.

It said Chris was moving east and was expected to turn north over the next couple of days, on a course that would keep it well away from land.

The Atlantic hurricane season officially runs from June 1 to November 30, though it is not unusual for storms to form earlier.

The hurricane center said that only twice before Chris, in 1887 and 1959, had the third storm of the Atlantic season formed earlier than June 19.

(Writing by Tom Brown; additional reporting by Jane Sutton; Editing by Jackie Frank)

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    Economic damage <em>(In 2010 Dollars)</em>: $11.8 billion Source: <a href="http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf">NOAA</a>/<a href="http://www.washingtonpost.com/blogs/wonkblog/wp/2012/11/05/is-sandy-the-second-most-destructive-u-s-hurricane-ever-or-not-even-top-10/">The Washington Post</a>

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    Economic damage <em>(In 2010 Dollars)</em>: $12.8 billion Source: <a href="http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf">NOAA</a>/<a href="http://www.washingtonpost.com/blogs/wonkblog/wp/2012/11/05/is-sandy-the-second-most-destructive-u-s-hurricane-ever-or-not-even-top-10/">The Washington Post</a>

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    Economic damage: $15.8 billion (April 2012 estimate) Source: <a href="http://www.noaanews.noaa.gov/stories2012/20120413_irene.html">NOAA</a>

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    Economic damage <em>(In 2010 Dollars)</em>: $15.8 billion Source: <a href="http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf">NOAA</a>/<a href="http://www.washingtonpost.com/blogs/wonkblog/wp/2012/11/05/is-sandy-the-second-most-destructive-u-s-hurricane-ever-or-not-even-top-10/">The Washington Post</a>

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    Economic damage <em>(In 2010 Dollars)</em>: $105.8 billion Source: <a href="http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf">NOAA</a>/<a href="http://www.washingtonpost.com/blogs/wonkblog/wp/2012/11/05/is-sandy-the-second-most-destructive-u-s-hurricane-ever-or-not-even-top-10/">The Washington Post</a>