The 2011 Atlantic hurricane season has ended and it's a study in contradiction.

The usual targets in the southeastern U.S. were spared, but Irene paralyzed the Eastern seaboard and left behind devastating and deadly flooding across the Northeast.

It was the sixth straight year without landfall of a major hurricane, yet Irene was one of the costliest storms in U.S. history and killed at least 47 people. Irene was not considered a major hurricane because it was not a Category 3 when it made landfall.

There were 19 tropical storms. That's the third-highest number on record. But there was only a slightly higher-than-average number of hurricanes, with six.

Tags: tropical storms, hurricane, hurricane season 2011, Irene