Lili, the most powerful storm of this year's Atlantic hurricane season to date, is bearing down on the U.S. state of Louisiana with sustained winds of 225 kilometers an hour.

Lili's out rain bands lashed the Louisiana coastline early Thursday, hours before the storm's expected landfall. A category 4 hurricane on a 1 to 5 scale, meteorologists say Lili is capable of extreme and extensive damage. In addition to high winds, the storm is expected to unleash powerful storm surges and torrential rains that could lead to life-threatening flood conditions.

Nearly half a million people were urged to evacuate coastal regions in Texas and Louisiana late Wednesday. Many residents spent the day boarding up homes and businesses before heading inland. New Orleans Mayor Ray Nagin had this advice. "Stay indoors," he warned. "Hunker down [protect yourself]. And keep your vehicles and people [family] off the streets for safety's sake."

Just a week ago, Louisiana was struck by another massive storm - Isidore - which caused $100 million in damage.