The hatched areas on the National Hurricane Center's tropical outlook map indicate "areas where a tropical cyclone — which could be a tropical depression, tropical storm or hurricane — could develop," said National Hurricane Center Deputy Director Jamie Rhome.

Erin is moving fast across the Atlantic, at 22 mph. It's forecast not only to become the Atlantic season's first hurricane, but also a major hurricane. A major hurricane is one that's a Category 3 or higher, with maximum sustained winds of at least 111 mph.