Hurricane Erin has strengthened to a Category 4 storm as it threatens to bring life-threatening surf and rip currents to the eastern coast of the United States. The rains caused by the storm are already beginning to hit the south-eastern Bahamas, and the Turk and Caicos Islands, where a tropical storm warning is in effect.

Hurricane Erin weakened overnight but remains a major hurricane, according to the latest advisory from the National Hurricane Center. A major hurricane is one that's a Category 3 or higher, with maximum sustained winds of at least 111 mph.