The remnants of Hurricane Isaac continue to cause headaches on Friday, bringing heavy rainfall and the threat of flash flooding to the lower Mississippi Valley as Gulf Coast residents get ready to start their cleanup efforts. The first hurricane to hit the United States this year will be remembered for striking New Orleans on the anniversary of 2005’s deadly Hurricane Katrina - and providing a first, successful test of the city’s pricey new flood defenses. New Orleans Mayor Mitch Landrieu concluded that the ring of defenses was "operating as designed."